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What are the first 20 elements on the periodic table?

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The periodic table currently contains 118 elements ordered according to their atomic number, which are organized in rows called periods and in columns called groups.

Despite there being so many elements, often knowing the characteristics of the first elements in each group in depth allows us to predict the properties of the other elements in their group. For this reason, it is common for chemistry teachers to ask their students to list the first elements of the periodic table. In some cases they are satisfied with the first 10, which completely cover the first two periods of the table, other times they are satisfied with 18, since this is how the first three periods are covered, while covering the most important representative elements of the table periodic. Other times, teachers even ask to memorize the first 20 elements of the periodic table in order to cover all the elements existing before the first transition metal.

There is a logical reason to shorten the list to the first 20 elements: the transition metals are characterized by having somewhat erratic and difficult to predict physical and chemical properties . Furthermore, the behavior of these properties is often difficult to understand for students who are just starting out on the path of learning chemistry.

With the intention of limiting the study of the elements and their properties to those that adequately illustrate the periodic properties of matter, below we will see a summary of the most relevant information on the first 20 elements of the periodic table.

What are the first 20 elements on the periodic table?

Since the elements are ordered by their atomic number, which at the same time represents the number of protons that the atoms of an element have in their nucleus, the first 20 elements are those that have the atomic numbers from 1 to 20. These are :

Atomic number (Z) element name chemical symbol Block Period Cluster element class 1 Hydrogen h yes 1 1 Non-metal two Helium I have yes 1 18 Non-metal 3 Lithium Li yes two 1 Metal 4 Beryllium Be yes two two Metal 5 Boron B. p two 13 Metalloid 6 Carbon C. p two 14 Non-metal 7 Nitrogen No. p two fifteen Non-metal 8 Oxygen EITHER p two 16 Non-metal 9 Fluorine F p two 17 Non-metal 10 Neon ne p two 18 Non-metal eleven Sodium na yes 3 1 Metal 12 Magnesium mg yes 3 two Metal 13 Aluminum To the p 3 13 Metal 14 Silicon Yes p 3 14 Metalloid fifteen Match P p 3 fifteen Non-metal 16 Sulfur S p 3 16 Non-metal 17 Chlorine Cl p 3 17 Non-metal 18 Argon ar p 3 18 Non-metal 19 Potassium k yes 4 1 Metal twenty Calcium AC yes 4 two Metal

Let’s see, below, some basic characteristics of these first 20 elements, including their year of discovery, the meaning of their name, the origin of their chemical symbol and some characteristic physical properties of each one.

#1 Hydrogen (H)

  • Discovery: Hydrogen was discovered by Henry Cavendish in 1766.
  • Origin of the name: It comes from the Greek terms hydro, which means water, and genes , which means to generate, to form. Therefore, hydrogen literally means ” water generator” , since the combustion of hydrogen produces water as the only product.
  • Physical state at 20 °C: Gas
  • Melting point: – 259.16 °C
  • Boiling point: – 252.16 °C
  • Description and uses: Hydrogen is a colorless and odorless gas of very low density. It is used in chemical synthesis, as well as a clean fuel and energy storage medium.

#2 Helium (He)

  • Discovery: Helium was discovered independently by Sir William Ramsay, Per Teodor Cleve and Nils Abraham Langlet in 1895.
  • Origin of the name: Its name comes from the Greek word for the sun, helios , because it was discovered studying the crown of the sun during an eclipse.
  • Physical state at 20 °C: Gas
  • Melting point: – 272.2 °C
  • Boiling point: – 268.93 °C
  • Description and uses: It is the lightest noble gas . It is an inert, colorless and odorless gas that is mainly used as a coolant when extremely low temperatures are required. It is also used in discharge lamps.

#3 Lithium (Li)

  • Discovery: Discovered by Johan August Arfvedson in 1817
  • Origin of the name: It comes from the Greek name for rock, lithos , because it was originally found in certain minerals.
  • Physical state at 20 °C: Solid
  • Melting point: 180.20°C
  • Boiling point: 1,342°C
  • Description and uses: It is the least dense metal of all. It has a silvery white color and reacts violently with water. It is used as an ion in the lithium batteries that power most of the mobile devices that exist today.

#4 Beryllium (Be)

  • Discovery: Discovered by Nicholas Louis Vauquelin in 1797.
  • Origin of the name: Its name comes from the Greek name for beryl, beryllo , the main mineral from which this element is extracted.
  • Physical state at 20 °C: Solid
  • Melting point: 1,287 °C
  • Boiling point: 2,468°C
  • Description and uses: Beryllium is the first member of the group of alkaline earth metals. Easily forms ions with +2 electric charge. It is relatively soft, not very dense, and has a light silver color.

#5 Boron (B)

  • Discovery: Discovered simultaneously in Paris by Louis-Josef Gay-Lussac and Louis-Jacques Thénard and in London by Humphry Davy in 1808.
  • Origin of the name: Its name comes from the Arabic word for borax, buraq .
  • Physical state at 20 °C: Solid
  • Melting point: 2,077 °C
  • Boiling point: 4,000°C
  • Description and uses: In its pure form it is a dark colored amorphous solid. One of its main uses is in the ignition systems of space rocket engines and in fireworks to give green colors.

#6 Carbon (C)

  • Discovery: It has been known since prehistoric times.
  • Origin of the name: It comes from the Latin word for carbon, carbo .
  • Physical state at 20 °C: Solid
  • Melting point: Sublimes at 3,825°C
  • Boiling point: Sublimes at 3,825°C
  • Description and uses: Carbon graphite is a black, brittle solid that is used as a conductor in some electrodes, as a lubricant in some motor oils, and in the manufacture of pencils. Its other common form, diamond, is a transparent crystalline solid and is the hardest material known to man.

#7 Nitrogen (N)

  • Discovery: Discovered by Daniel Rutherford in 1772.
  • Origin of the name: It comes from the Greek terms nitron and genes that mean nitro and generate, respectively. Nitrogen means, then, nitro generator, which is a mineral that contains potassium nitrate.
  • Physical state at 20 °C: Gas
  • Melting point: – 210.0 °C
  • Boiling point: – 195.80 °C
  • Description and uses: Nitrogen is a colorless gas that makes up almost 80% of the air we breathe. It has many uses ranging from the synthesis of fertilizers to explosives.

#8 Oxygen (O)

  • Discovery: Discovered simultaneously by Joseph Priestley and Carl Wilhelm Scheele in 1774.
  • Origin of the name: It comes from the Greek terms oxy and genes that mean acid and generate, respectively. Etymologically, oxygen means acid generator.
  • Physical state at 20 °C: Gas
  • Melting point: – 218.79 °C
  • Boiling point: – 182.962 °C
  • Description and uses: It is also a colorless and odorless gas. It forms almost 21% of the dry air . It is essential for the life of aerobic living beings. In industry it is used as an oxidant in different processes including welding and flame cutting systems.

#9 Fluorine (F)

  • Discovery: Discovered in 1886 by Henri Moissan.
  • Origin of the name: It comes from the Latin fluere which means to flow.
  • Physical state at 20 °C: Gas
  • Melting point: – 219.67 °C
  • Boiling point: – 188.11 °C
  • Description and uses: Fluorine is a light green poisonous gas. It is the most electronegative element in the periodic table and its compounds, such as hydrofluoric acid, can attack and dissolve glass.

#10 Neon (Ne)

  • Discovery: Discovered by Sir William Ramsay and Morris Travers in 1898.
  • Origin of the name: It comes from the Greek neos , which means new.
  • Physical state at 20 °C: Gas
  • Melting point: – 248.59 °C
  • Boiling point: – 246.046 °C
  • Description and uses: It is a colorless noble gas widely used for the manufacture of colored lamps.

#11 Sodium (Na)

  • Discovery: Discovered by Humphry Davy in 1807.
  • Origin of the name: It comes from the English word soda , which refers to caustic soda or sodium hydroxide. Its chemical symbol is Na due to the Latin name for this substance, natrium .
  • Physical state at 20 °C: Solid
  • Melting point: 97,794°C
  • Boiling point: 882,940°C
  • Description and uses: It is the second alkaline metal. Like lithium, it is a soft, silvery-white metal that is highly reactive with water. It is used in chemical synthesis for different purposes and is one of the most common ions in water-soluble salts.

#12 Magnesium (Mg)

  • Discovery: Discovered by Joseph Black in 1755.
  • Origin of the name: It comes from the name of the Magnesia district of a Greek city.
  • Physical state at 20 °C: Solid
  • Melting point: 650°C
  • Boiling point: 1,090 °C
  • Description and uses: It is a silver-colored alkaline earth metal used in fireworks and sparklers because it burns with a very bright light in air. It is also used as an additive in the preparation of aluminum alloys.

#13 Aluminum (Al)

  • Discovery: Hans Oersted discovered it in 1825.
  • Origin of the name: It comes from the Latin term alumen , which means bitter salt.
  • Physical state at 20 °C: Solid
  • Melting point: 660.323 °C
  • Boiling point: 2,519°C
  • Description and uses: It is a light, silvery and quite resistant metal. It is used in the manufacture of cans to contain liquids and in construction materials.

#14 Silicon (Yes)

  • Discovery: Discovered by Jöns Jaco Berzelius in 1824
  • Origin of the name: It comes from the Latin word for flint, flint .
  • Physical state at 20 °C: Solid
  • Melting point: 1,404 °C
  • Boiling point: 3,265 °C
  • Description and uses: This is the first example of a metalloid or semimetal. This element forms the basis of all modern electronics, representing the main material from which all the integrated circuits that make every electronic device that exists work.

#15 Phosphorus (P)

  • Discovery: Discovered in 1669 by Henning Brandt.
  • Origin of the name: It comes from the Greek term phosphoros , which means bearer of light. This same term is also the origin of the chemical symbol P.
  • Physical state at 20 °C: Solid
  • Melting point: 44.15 °C
  • Boiling point: 280.5°C
  • Description and uses: This non-metal is of great importance for the manufacture of fertilizers, but it is also used in its pure state as a flammable material in matches and as a spontaneous combustion fuse in hand grenades and other types of explosives.

#16 Sulfur (S)

  • Discovery: Known since prehistoric times.
  • Origin of the name: Both its name and its chemical symbol come from the Latin term sulfurium .
  • Physical state at 20 °C: Solid
  • Melting point: 115.21 °C
  • Boiling point: 444.61 °C
  • Description and uses: In pure form it is a yellow crystalline solid found near volcanoes. It is used in the synthesis of sulfuric acid, the world’s most important commercial and industrial acid. It is also used in the vulcanization of rubber.

#17 Chlorine (Cl)

  • Discovery: Discovered in 1774 by Carl Wilhelm Scheele
  • Origin of the name: It comes from the Greek word to describe the greenish-yellow color, chloros .
  • Physical state at 20 °C: Gas
  • Melting point: – 101.5 °C
  • Boiling point: – 34.04 °C
  • Description and uses: Chlorine is a poisonous and highly reactive gas, with a very faint greenish-yellow color. Both in its elemental state and in the form of some oxisalts, it is effective in killing and preventing the growth of many microorganisms, which is why it is used as a disinfectant.

#18 Argon (Ar)

  • Discovery: Discovered by Sir William Ramsay and Lord Rayleigh in 1894.
  • Name Origin: His name is derived from argos , which is Greek for slow or sluggish.
  • Physical state at 20 °C: Gas
  • Melting point: – 189.34 °C
  • Boiling point: – 185.848 °C
  • Description and uses: This noble gas is used as an inert atmosphere in many applications ranging from the manufacture of incandescent light bulbs to chemical analysis. It is the most abundant noble gas and forms almost 1% of our Earth’s atmosphere.

#19 Potassium (K)

  • Discovery: Again, this alkali metal was discovered by Humphry Davy, also in 1807.
  • Origin of the name: The name comes from the English word potash , which means potash and refers to the main compound that we can find in the ash of certain woods. The chemical symbol K, instead, comes from the Latin term for the same potash, kalium .
  • Physical state at 20 °C: Solid
  • Melting point: 63.5°C
  • Boiling point: 759 °C
  • Description and uses: It is an extremely reactive metal. It oxidizes immediately on contact with air and can even react with moisture present in it, so it must be stored sealed in an inert atmosphere or submerged in oil. It is an important part of many fertilizers.

#20 Calcium (Ca)

  • Discovery: Discovered by Humphry Davy in 1808.
  • Origin of the name: It comes from the Latin name for lime, calx .
  • Physical state at 20 °C: Solid
  • Melting point: 842 °C
  • Boiling point: 1,484°C
  • Description and uses: Silvery alkaline earth metal found abundantly in nature. It is an essential component of our diet, forming an important part of the bone structure and the functioning mechanism of our nervous and muscular systems. Elemental calcium is used as a reducing agent in obtaining other metals from its ores.

References

BYJU’S. (2021, March 22). First 20 Elements . BYJUS. https://byjus.com/chemistry/first-20-elements/

Chang, R. (2012). Chemistry ( 11th ed.). McGraw-Hill Education.

Helmenstine, A. (2022, February 23). What Are the First 20 Elements – Names and Symbols . Science Notes and Projects. https://sciencenotes.org/first-20-elements-of-the-periodic-table/

The Editors of Encyclopaedia Britannica. (2020, November 4). helium | Definition, Properties, Uses, & Facts . Encyclopedia Britannica. https://www.britannica.com/science/helium-chemical-element

Vedanthu. (2022, February 2). First 20 Elements . https://www.vedantu.com/chemistry/first-20-elements-of-periodic-table

What is a hydroxyl group?

In chemistry, a hydroxyl group is a group of atoms formed by an oxygen atom with two unshared pairs of electrons; on the one hand it is linked to a hydrogen atom by means of a single covalent bond, and on the other it can be linked to a carbon chain in an organic compound, to some other non-metal (for example, sulfur, nitrogen, etc.) , or it may not be bonded to any other atom but have an unpaired electron.

The word hydroxyl literally means a radical made up of hydrogen and oxygen. Here, the word radical can be used, in the context of organic chemistry, to refer to an atom or, in this case, a group of atoms that replaces a hydrogen in a hydrocarbon. On the other hand, it can also refer to a free radical with an electron deficient oxygen that has one unpaired electron.

In some cases, the hydroxyl group is confused with the hydroxide anion. This is a very common mistake, but there are very important differences between one and the other. The most notorious of all is that, while the hydroxyl group is an electrically neutral group, the hydroxide is an anion (that is, it has a negative charge). On the other hand, the hydroxyl free radical is a very reactive and unstable chemical species while the hydroxide anion is reactive, but not so much.

The following figure shows the different forms in which you can find spices made up of hydrogen and oxygen.

Different types of groups with hydrogen and oxygen

To avoid confusion, from now on we will refer to the hydroxyl group as the central structure of the previous figure, that is, as part of a molecule in which oxygen is directly linked to a carbon chain or to another non-metal.

Properties of the hydroxyl group

is a polar group

Because oxygen is more electronegative than hydrogen, the covalent bond between these two atoms is polarized, with the partial negative charge on the oxygen atom. This makes most organic compounds that have a hydroxyl group, such as alcohols, polar compounds.

Can form hydrogen bonds

The polarity of the OH bond means that the hydroxyl group can act as a hydrogen donor in a hydrogen bond. In addition, the oxygen of the hydroxyl group has two lone pairs of electrons, so it can also receive two hydrogen bonds as an acceptor. In other words, the hydroxyl group can form a total of three simultaneous hydrogen bonds.

It is a Brønsted-Lowry acid.

Again because of the polarity of the OH bond, and also because oxygen has a good ability to bear a formal negative charge by losing the hydrogen, the hydroxyl groups can give up the proton by acting like a Brønsted-Lowry acid.

The particular pKa value or acidity of the hydroxyl group will depend on the structure of the rest of the molecule to which it is attached. If –OH is directly attached to a carbonyl group (as in carboxylic acids), then it will be highly acidic, with pKa values ​​in the order of 3 to 5. If it is attached to an aromatic group, as in the case of phenols, their pKa will be in the order of 7 to 10; if it is linked to an aliphatic chain, its pKa will be 15 or more.

Can act as a Lewis base

The fact that the OH group has two unpaired pairs of electrons means that it can also act as a base, donating an electron pair to a proton or some other electron-deficient species (Lewis acid). Simply put, it can be protonated by a strong enough acid.

Functional groups that have a hydroxyl group

The hydroxyl group by itself is not a functional group, as it depends on what it is attached to. In the case of organic compounds, the most common functional groups that have hydroxyl groups are:

alcohols

Alcohols are the simplest functional group that possesses a hydroxyl group. In this case, the oxygen is directly bonded to a saturated aliphatic carbon. Alcohols are generally represented as follows:

where R represents an alkyl group.

These are polar compounds, most are soluble in water, and are liquid at room temperature.

enols

The main difference between an alcohol and an enol is that in the second case the hydroxyl group is attached to an unsaturated carbon atom with sp 2 hybridization and that it is attached to another carbon by a double covalent bond, as shown in the following figure. .

This double bond stabilizes the conjugate base by resonance, so enols are usually more acidic than alcohols.

phenols

Phenols are very similar to alcohols except that, in this case, the hydroxyl group is attached to a carbon that is part of an aromatic ring.

An example of this type of compound is phenol, which has the following structure:

As in the case of enols, the aromatic ring is able to stabilize a negative charge on oxygen by means of resonance, so phenols are always considerably more acidic than alcohols.

Carboxylic acids

Carboxylic acids or organic acids have a hydroxyl group linked to a carbonyl.

The presence of the carbonyl double bond stabilizes the conjugate base by resonance after losing the proton. But, in addition to this, it distributes this negative charge between the two oxygens, which is much more favorable than distributing it on carbons, as happens in the two previous cases. This gives these hydroxyl groups greater acidity than in the other cases; for this reason these compounds are called acids.

sulfonic acid

This is an example of a functional group that has a hydroxyl group, but in which it is not bonded to a carbon but to another heteroatom, in this case, sulfur.

The multiple resonance structures mean that compounds that possess this functional group are also acidic in character.

References

Carey, F., & Giuliano, R. (2014). Organic Chemistry ( 9th ed.). Madrid, Spain: McGraw-Hill Interamericana de España SL

Functional Groups and Organic Nomenclature . (2020, October 29). Retrieved from https://espanol.libretexts.org/@go/page/2313

Alcohols and Ethers . (nd). (2021, January 9). Retrieved from https://espanol.libretexts.org/@go/page/1973

Smith, MB, & March, J. (2001). March’s Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 5th Edition (5th ed.). Hoboken, NJ: Wiley-Interscience.

Definition of suspensions

A suspension is a heterogeneous mixture in which some particles are left out of the resting mixture . The particles that make up a suspension, being much larger than those of a solution, leave the dispersing phase due to the action of gravity.

While the particles in a solution are less than two nanometers, in a suspension the particles can be larger than 1,000 nanometers. On the other hand, the suspensions, since they are heterogeneous mixtures, the substances that are in them can be identified, which can be separated from the dispersing medium by filtration.

Difference Between Solutions, Colloids, and Suspensions

These three terms are often used interchangeably, but they are different, each defining them:

  • Solutions : are homogeneous mixtures formed by substances whose particles intermingle at the atomic or ionic level. Some examples of solutions are: salt in water, ethyl alcohol in water, gases that make up air, metals that form an alloy.
  • Colloids – The size of the particles is approximately 10 to 100 nm, and two phases are present. A colloid is on the borderline of homogeneous and heterogeneous mixture. It does not separate on standing, and its appearance is not transparent as it happens in solutions. Colloids are made up of a dispersed phase and a dispersing medium; Depending on the physical state of these phases, there are different classes of colloids, such as emulsions, foams, aerosols, etc.
  • Suspensions : the particles are larger than 100 nm in size and there are two phases present, so there is a heterogeneous mixture, which separates when it is allowed to settle, and the appearance, therefore, is not transparent, as happens in suspensions. solutions.

Blood colloid or suspension?

Blood can be defined as a colloid and also as a suspension. It is a suspension because the cells are in aqueous solution, but it is also a colloid since it has a liquid phase, which is plasma, and another solid phase, such as cells and platelets. According to this, the dispersant phase would correspond to the plasma, while the dispersed phase would correspond to the solid elements, that is, the cells.

Is milk a suspension?

Milk is a complex mixture of water, proteins, fats, carbohydrates, and minerals. While carbohydrates and minerals are soluble in water, fats and some of the proteins do not dissolve and remain in suspension.

Examples of suspensions

  • Mixture of flour and water.
  • Mixture of chalk and water.
  • Muddy water.
  • Mixture of sand and water.
  • Water based paints
  • Mix slaked lime (calcium hydroxide) in water.
  • Mixture of magnesium hydroxide and water.
  • Lemonade.

Sources

Phase Diagram Definition

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A phase diagram is a graphical representation of the different states of thermodynamic equilibrium of a system under different conditions. This type of graph allows us to predict, among other things, the phases that are present under certain conditions, as well as the proportion in which each phase is found and its composition, in the case of binary mixtures or more complex mixtures.

Types of phase diagrams

Single component phase diagrams (pure substance diagrams)

These diagrams show the different phases or states of aggregation in which a pure substance can be found at different values ​​of temperature and pressure. These phase diagrams can become very complex, especially in the solid phase, where temperature and pressure conditions can favor the formation of multiple different crystal structures with markedly different properties.

The typical shape of a phase diagram for a pure substance is shown below:

Phase Diagram Definition Typical phase diagram of a pure substance, such as water.

Two examples of typical phase diagrams of a pure substance are those of elemental carbon and helium, which are shown in the following figure. Carbon , a nonmetal , can occur in different solid allotropes (graphite and diamond); It can also occur in a liquid and gaseous state. In the case of helium, this is a gas that cannot be easily liquefied.

Phase Diagram Definition

Phase diagrams of binary systems (two-component diagrams)

Binary phase diagrams consist of a graphical representation of the phases that form at different temperatures or at different pressures in a system made up of two components (binary system) as a function of the total composition of the system (usually represented on the X axis).

Depending on the particular components of the mixture, these systems can give rise to different types of phase diagrams. In some of these diagrams separate phases of the pure components are formed in different states of aggregation (solid, liquid or gas), while in other cases homogeneous phases of both components are formed.

Two binary phase diagrams are shown below. The former is an example of a binary system that forms a eutectic mixture, while the latter does not.

Phase Diagram Definition Phase Diagram Definition

Phase diagrams of ternary systems (diagrams of three components)

In these diagrams a triangle is used to represent, on each side, the composition of each of the three binary systems that can be formed between three components. Any point inside the triangle represents a ternary system of definite composition.

In these cases, the concentration of each species should be represented, either as a mole fraction or mass fraction (to ensure that all fractions sum to 1) or as a percentage (to ensure that the total concentration always adds up to 100%). ).

Definition of a phase diagram

For each possible composition of the system, at a fixed temperature and pressure, the phase or phases that are present are shown.

Construction of a phase diagram

The process of construction of a phase diagram can be carried out either theoretically or from experimental information. In the first case, thermodynamic equations are used to calculate the equilibrium state of a system (be it a pure substance, a binary mixture or a ternary system) depending on the properties of the system and its composition. Except for relatively simple systems, this approach is considerably complex and difficult to carry out.

From an experimental point of view, the procedures used to build phase diagrams are usually similar, regardless of the type of phase diagram in question. In most cases, what is sought is to start from a system in an initial state well defined from the point of view of its composition and other properties, and it is observed in some way (with the naked eye or through instrumental techniques). ) which phase or phases are present. Then gradually vary some of the properties of the system, keeping all other properties constant, taking note of any change of state and of the conditions under which this change of state occurred.

Construction of diagrams of pure substances

In the case of pure substances , a pressure is usually set and then the temperature is varied, representing the phase change points at the height of the corresponding pressure on the diagram. Then the pressure is changed and the process is repeated. The union of the points where the phase changes occur and the intersections between the resulting curves allow the construction of the phase diagram, indicating in each region on each side of each curve which phase is present.

Construction of binary diagrams

In the case of binary systems, one normally starts with the two pure components at a defined pressure or temperature and varies the other variable (temperature or pressure, respectively), again noting the temperature or pressure at which some phase change occurs. These points are represented on the vertical axes. The one on the right represents one of the pure components and the one on the left the other.

Then, mixtures of both components are prepared with concentrations defined in terms of their mole or mass fraction (or their percentages). For each composition (plotted on the x-axis) again vary the temperature or pressure and note the phase changes as before.

Construction of ternary diagrams

The procedure for ternary diagrams is usually a bit more complex. In some cases, the aim is to prepare mixtures that run parallel to one of the sides of the diagram, in other cases it is done perpendicularly and in other cases diagonally. Each of these tours has its own particular experimental way of being achieved, including mixing a fixed binary system with increasing amounts of the third component and vice versa, among others.

What are phase diagrams used for?

The application of phase diagrams depends on the particular type of phase diagram in question.

Utility of phase diagrams of pure substances

In the case of diagrams of pure substances, the phase diagram provides us with clear information about the phase in which the system will be as a function of pressure and temperature. Thanks to this, it also allows us to predict the phase changes that must occur when we take a system from an initial state to a final one through different paths.

On the other hand, this type of phase diagrams also makes it possible to predict the phase change temperatures (or phase change points) of a pure substance at different pressures. For example, we can clearly see how the boiling and melting points change as a function of pressure.

Utility of binary phase diagrams

In the case of binary phase diagrams, these offer information about the different phases, their proportions and their composition when we vary, either the temperature keeping the pressure constant, or the pressure keeping the temperature constant. Being two-dimensional diagrams, it is generally not possible to simultaneously observe phase changes, the proportions in which each phase is present, and its composition as a function of temperature and pressure. However, the construction of binary phase diagrams as a function of temperature at different pressures can provide us with this information indirectly.

Phase diagrams of binary systems allow us to study the interactions between the different phases that can form between two different chemical substances. These phases can include pure phases of both components in different states (solid and liquid, for example) or homogeneous phases containing both components (such as alloys, solutions, co-crystals, etc.).

Thanks to the above, binary phase diagrams allow the identification of eutectic systems, which are binary systems that melt at a single temperature and whose melting point is lower than that of either of the two pure components. In addition, they allow the determination of the melting temperature of this system, known as the eutectic point. This is very important in various industrial applications, as it allows the identification and design of high-strength, low-melting metal alloys useful, for example, in welding.

Utility of ternary phase diagrams

Finally, in ternary phase diagrams, a triangular diagram is used to be able to simultaneously represent at one point the proportions in which the three components of a ternary mixture are found. This means that in these diagrams we cannot observe the effect of temperature and pressure on the phase(s) present in the ternary system, but only the effect of composition.

Therefore, a ternary phase diagram is mainly used to determine how a ternary system behaves when the relative concentration of one of the components varies. This is useful for studying systems in which two solutions with different solutes are mixed, since the solvent and the two solutes will be present in the mixture, thus forming a ternary system.

Parts of a phase diagram

The following diagrams are used to describe the parts of a phase diagram for a pure substance and a binary system:

Phase Diagram Definition Phase Diagram Definition

The axes of the graph

Depending on the type of phase diagram, these can represent pressure and temperature (as in the case of the first diagram), mole fraction of one component (as in the second), or of two components (as in the case of ternary diagrams). ).

Phase equilibrium curves

They are the curves that separate one phase from another in a phase diagram. The AB, BC, and BD curves in the above diagram of a pure substance are all examples of phase equilibrium curves, as are the AB and AD curves in the second diagram.

triple points

In systems of pure substances, the triple point is the one in which several phase equilibrium curves coincide, so there are 3 phases in simultaneous equilibrium. It corresponds to point B in the first diagram of the previous figure.

Critical points

It corresponds to point D in the first diagram. It indicates the maximum temperature at which a pure substance can exist as a liquid. Above this temperature, the substance is always gaseous and at higher temperatures and pressures it behaves like a supercritical fluid.

eutectic points

It corresponds to point A in the binary diagram of the previous image. It is the point at which both phases melt together going directly from the solid state to the liquid state with neither of the two original solid phases remaining present. This point marks both the eutectic melting temperature and the eutectic composition for the considered binary system.

Not all mixtures form eutectic mixtures, but many, such as alloys, do.

References

Agudelo, AF, & Restrepo, OJ (2005, January 21). THERMODYNAMICS AND PHASE DIAGRAMS . sciELO. http://www.scielo.org.co/scielo.php?script=sci_arttext&pid=S0012-73532005000100002

Binary Phase Diagram . (2014, April 9). Chemical Zone. http://zona-quimica.blogspot.com/2014/04/diagrama-de-fases-binario.html

Lopez, JR (sf). Phase diagrams . Junta de Andalucía. https://www.juntadeandalucia.es/averroes/centros-tic/21700290/helvia/aula/archivos/repositorio/0/42/html/diagram.html

Material Engineering. (2018, January 20). Phase Diagram: Meaning and Types . Engineering Notes India. https://www.engineeringenotes.com/engineering/phase-diagram/phase-diagram-meaning-and-types-material-engineering/34506

Novelo-Torres, AM, & Gracia-Fabrique, J. (2010, October 1). Trajectories in ternary diagrams . Elsevier. https://www.elsevier.es/es-revista-educacion-quimica-78-articulo-trayectorias-diagramas-ternarios-S0187893X18300995

Definition and Examples of Colloids

Colloids or colloidal suspensions are homogeneous mixtures of substances that do not separate or settle but are heterogeneous on a microscopic scale. Colloidal mixtures have two parts: the particles or colloids themselves and the medium in which they are dispersed. The size of a colloid is larger than that of a molecule, which differentiates a colloidal mixture from a solution, but they are small enough to differentiate them from suspended particles. In smoke, for example, the particles caused by combustion are suspended in a gas.

Colloids are extremely important in the manufacture of various industrial materials such as paints, plastics, insecticides and cements. They are also used in the pharmaceutical industry and in biomedical applications. Let’s see some examples.

Colloidal suspensions are basically formed in two ways. One of them is by drops or particles that are dispersed in a certain medium by the effect of a spray, by grinding, by injection at high speed or by agitation. The other is by dissolved substances that precipitate or condense into small particles within the solute due to pH changes, REDOX reactions, or temperature or pressure changes.

At first sight it seems difficult to differentiate a colloidal suspension from a solution or from a suspension of particles , since in the definition they only differ by the size of the particles dispersed in a certain medium. However, let’s see two simple ways to identify a colloidal suspension. In a suspension the particles settle over time, while in a colloidal suspension the colloids are always dispersed in the medium. On the other hand, if a light beam is made to shine on a colloidal suspension, the Tyndall effect will be observed, causing the light beam to be scattered by the colloids. An example is car headlights scattered by fog.

Examples of colloidal suspensions or mixtures

Aerosols are colloidal suspensions, some examples being fog, a dispersed insecticide, clouds, and smoke. Fluid foams, such as heavy whipping cream or shaving foam, and solid foams, such as marshmallows and Styrofoam, are examples of colloidal suspensions. So are emulsions, such as milk, mayonnaise, and lotions; gels, such as gelatin, butter and jelly; liquid suspensions, such as ink, gum, and detergent; and solid suspensions, such as pearls, gems, some colored glass, and some alloys.

To better understand the concept, let’s differentiate some examples according to the type of colloid and the medium in which it is dispersed.

  • A solid in a gas: smoke.
  • A liquid in a gas: the fog.
  • A solid in another solid: glass.
  • A gas in a liquid: shaving foam.
  • A gas in a solid: the pumice stone.
  • A solid in a liquid: butter.

Font

Valenzuela, C. General Chemistry: Introduction to theoretical chemistry. Editions of the University of Salamanca, Spain. nineteen ninety five.

What is an Atomic Mass Unit or AMU?

The atomic mass unit (amu), also called the unified atomic mass unit or dalton (Da), is a very small unit of mass used to express the mass of atoms in terms of the mass of an atom of the isotope of carbon 12 . It is defined as one twelfth the mass of the carbon-12 atom when it is not bonded to any other atom.

The definition of the atomic mass unit assigns the carbon-12 atom a mass of exactly 12 amu. Using this unit, the mass of all other atoms is expressed as a multiple or submultiple of the mass of the carbon-12 atom. For this reason, at the time of its creation, the atomic mass unit was just another relative scale of atomic mass, similar to others that had already been postulated up to then. However, when the actual mass of the carbon atom was determined and the absolute value of the atomic mass unit could thus be established, the amu became an absolute scale of mass in the same way as the gram, pound, and ton. .

The value of the atomic mass unit

The concept and value of the atomic mass unit is linked to the original concept that Avogadro proposed for the mole. He defined a mole as the number of particles in exactly 12 grams of a 100% pure sample of the carbon-12 isotope. At the time, this number was not known, but today it is; its value is called Avogadro’s number and is approximately 6,022.10 23 (the currently accepted value for this number is exactly 6,0221367.10 23 particles per mole).

Once Avogadro’s number is determined, the mass of a single carbon 12 atom can be known. Dividing this value by 12 gives the value of the atomic mass unit. The relationship is very simple:

If, by definition, one mole of carbon-12 atoms weighs exactly 12 grams, and we know that there are 6,0221367.10 23 atoms in 1 mole, then each carbon-12 atom weighs:

mass of carbon atom

Now, using the definition of the atomic mass unit, we get:

atomic mass unit value atomic mass unit value

Therefore, the atomic mass unit has a value of 1,660540.10 -27 kg

Why use the uma?

Any mass, including that of an atom, can be expressed in any unit of mass, from grams, pounds, and ounces to metric tons; however, some are more convenient than others depending on the case. For example, it is common to represent our own weight in pounds or kilograms, but not tons. Nor would we express the mass of a Boeing 747 in grams or milligrams; we would probably do it in tons.

Using this same logic, and considering that atoms are extremely small, it is not convenient to use any of these units to express atomic mass. That is why the atomic mass unit exists, since it allows the mass of atoms to be represented in a more convenient way.

Since atoms are very small, one would expect the atomic mass unit to be equally small.

The atomic mass unit and the mass number

A coincidence both fortunate and unfortunate is that the definition of the atomic mass unit causes the expressed masses of atoms to have a numerical value very similar to the known mass number. The latter indicates the total number of nucleons, that is, of protons and neutrons that are present in the nucleus of an atom. In fact, in the case of the carbon-12 atom, 12 indicates precisely the mass number and, only for this atom, this number exactly coincides with the mass of the atom expressed in amu.

Since the carbon-12 nucleus contains 6 protons and 6 neutrons, the atomic mass unit represents, in a way, an average mass between the two nucleons. For this reason, for most atoms the mass number is very similar to its atomic mass expressed in amu. However, they are not the same, nor do they even refer to the same physical quantities. The mass number is not a mass, although its name suggests it.

The atomic mass versus the molar mass of an atom

Finally, it is worth making an additional clarification around the terms atomic weight, atomic mass and molar mass of an atom. When we talk about atomic weight or atomic mass, we mean the weight or mass of a single atom. For example, expressed in daltons, the atomic mass of carbon-12 is 12 amu, as we saw before.

However, it is common for many students to say, wrongly, that the atomic mass of carbon is 12 g or worse, 12 g/mol. The first error is considerably serious, since a single carbon atom, something so small that it can only be seen through the world’s most advanced microscopes, is being said to have a mass of 12 g, which might well be equivalent to a large spoonful of sugar.

The second mistake is much more common, so much so that many professional chemists commit it: they are confusing the atomic mass (that is, the mass of one atom) with the molar mass of an atom (that is, the mass of one mole of atoms). ). The confusion arises from the fact that, due to the definition of the atomic mass unit and the mole, the molar mass in g/mol is numerically equal to the atomic mass in amu.

Examples of the use of the atomic mass unit

  • The mass of a carbon-13 atom in atomic mass units is 13.003355 amu.
  • The average atomic mass of the element carbon (not of a particular atom of carbon) is 12.0107 amu (this consists of the weighted average of the masses of the naturally occurring isotopes of carbon, C-12 and C-13) .
  • PG5 polymer is the largest molecule ever created by man and has a mass of more than 200 million daltons or amu. The following image shows the structure of the monomer that constitutes it.

PG5 - the largest molecule created by man PG5 – the largest molecule created by man

  • The DNA molecule of the human genome has approximately 3.3 billion base pairs, and a mass of approximately 2.2.10 12 amu.

dna molecule dna molecule

  • The mass of a person who weighs 75 kg in atomic mass units is 4,417.10 28 amu.

References

Everything you need to know about saturated solutions in chemistry

A saturated solution is one that does not admit the dissolution of more solute. In other words, it is a solution in which the maximum concentration of solute that can be dissolved in that particular solvent and at a particular pressure and temperature has already been reached. These are solutions in which the solubility equilibrium has been established between the solute dissolved in the solvent and the solute in the solid state at the bottom of the container, in the liquid state either above or below the solvent (depending on the densities) or in a gaseous state.

solubility equilibrium

As just mentioned, a solution is saturated when the solubility equilibrium is reached. In the simplest case, this equilibrium can be represented by the following chemical equation:

Solubility equilibrium of a molecular solute to define a saturated solution

Where S represents a molecular solute (which does not dissociate) and the subscripts indicate if it is pure and in a solid state, or if it is dissolved (ac means in aqueous solution, although it could be in any other solvent).

When you have molecular solvents as in this case, to obtain a saturated solution and equilibrium can be established, it is necessary that the concentration of the solute in the solution is equal to the equilibrium constant, Ks, and that there is still some solute left. in undissolved solid state.

In the case of ionic solutes such as salts, the general reaction looks like this:

Solubility equilibrium of an ionic solute and the solubility product constant to define saturated solutions

where K ps is the solubility product constant, [M m+ ] eq represents the molar concentration of the cation M m+ in the saturated solution and [A n- ] eq represents the molar concentration of A n- in the saturated solution.

In this case, the condition that defines the saturated solution is that the product of the concentrations of the ions in solution (M m+ and A n- ) raised to their respective stoichiometric coefficients (nym) must be equal to the constant of the product of solubility. If the result is greater than K ps , the solution is supersaturated, and if it is less, it is unsaturated.

The equilibrium of the saturated solution is dynamic.

When a saturated solution is achieved, it appears that the solute is no longer dissolving in the solvent and that the dissolution process has stopped. However, this is not exactly so. In fact, as in most chemical equilibria, the solubility equilibrium is not a static equilibrium but a dynamic one, in which the forward reaction (dissolution of more solute) and the reverse reaction (precipitation of solute from solution) They are happening at the same rate. For this reason, no change is noted either in the net amount of solid solute or in the concentration of the solute in the solution.

Ways to obtain a saturated solution

There are three basic ways to obtain saturated solutions:

  1. Add solute until no more dissolves , no matter how vigorously the solution is shaken. This is the simplest method, although it can sometimes be very tedious since there are solutes that dissolve very slowly.
  2. The second way is to start from an unsaturated solution and start evaporating the solvent . As the total volume of the solution decreases without loss of solute, the concentration of the solute will increase until the maximum concentration (or solubility) is reached. At that moment the solute will begin to precipitate and from then on you will have a saturated solution.
  3. Another way is to dissolve more of the solute than the solvent can handle through heating . By allowing this solution to cool , a supersaturated solution will be obtained. For this reason, any disturbance, from a vibration to seeding a small crystal on the surface of the solution, will immediately trigger precipitation of excess solute. This precipitation will cease as soon as the saturation level is reached.

There is a fourth way to obtain saturated solutions from unsaturated solutions that consists of progressively modifying the medium or the solvent to reduce the solubility of the solute. This can be accomplished by adding an organic solvent, changing the pH, and in other ways as well.

Factors Affecting Solubility Equilibrium and Saturated Solutions

The nature of the solute and solvent

Each chemical compound has its solubility in each different type of solvent. For example, sugar is much more soluble than salt in water, so it will always be easier to saturate a solution with salt than with sugar. There are also cases in which it is impossible to obtain a saturated solution. Such is the case of solutes that are miscible with the solvent, such as solutions of ethyl alcohol and water, which can be mixed in any proportion.

Temperature

As seen just now, temperature plays an important role in saturated solutions, since an increase in temperature can increase solute solubility, dissolving all solid solute and turning a saturated solution into an unsaturated one.

On the other hand, the effect of temperature on the solubility of gases is just the opposite. Instead of increasing its solubility, high temperatures decrease it. Proof of this is the case of soft drinks. These lose most of their gases with increasing temperature.

pH

In those cases in which the solute has acid-base properties, the pH can play a very important role in determining its solubility. In general, any reaction that helps to further ionize the solute will increase its solubility, which can turn a saturated solution into an unsaturated one.

For example, if the solute is a weak acid such as benzoic acid and you have a saturated solution, adding sodium hydroxide that reacts with said acid and ionizes it will help dissolve more of the solute in the solution.

The pressure

Pressure affects gaseous solutes the most. Strongly increasing the pressure of gases above a solution can force the gas to dissolve in greater quantity in the solvent. This would be the equivalent of increasing the temperature for solid solutes. In the case of gases, as long as the solution and the gas are confined in a sealed container, no matter how much the pressure is, the solution will always end up gas saturated if given enough time.

common ion effect

The common ion represents an effect similar to that of pH. When it is desired to dissolve an ionic solute in a solution, it will dissociate and produce a certain concentration of its respective ions. If we try to dissolve the same ionic solute in a solution that already contains some of one of its ions, it will be more difficult to dissolve it than if we did it in the pure solvent. This is called the common ion effect and makes it easier to saturate solutions.

Examples of saturated solutions

Sealed fizzy drinks

All soft drinks, sodas, and carbonated beers are saturated solutions of carbon dioxide in water as long as the bottle or can is completely sealed.

The moment the bottle is uncorked, the equilibrium is lost and the solution suddenly becomes a supersaturated solution, so the gases begin to bubble, escaping.

The water on the shores of the dead sea

The Dead Sea is one of the saltiest lakes on earth, and on the shore you can see the crystallization of salt that comes from the lake water. This means that, in some parts, the water has been trapped in small puddles that, when they evaporate, become saturated with salt and begin to precipitate.

some types of honey

There are some types of honey that are more concentrated than others, and in some cases, they are so concentrated that the sugars they contain begin to crystallize in the bottle.

This shows that the solution was originally supersaturated, and that, after crystallization, it became a saturated solution.

References

Brown, T. (2021). Chemistry: The Science Center. (11th ed.). London, England: Pearson Education.

Chang, R., Manzo, Á. R., Lopez, PS, & Herranz, ZR (2020). Chemistry (10th ed.). New York City, NY: MCGRAW-HILL.

Flowers, P., Theopold, K., Langley, R., & Robinson, WR (2019). Chemistry 2e . Retrieved from https://openstax.org/books/chemistry-2e

Bubis, M. (1998). The Dead Sea – An Unusual Sea. Retrieved from http://sedici.unlp.edu.ar/bitstream/handle/10915/49306/Documento_completo.pdf

Honey and temperature (nd) Retrieved from https://www.latiendadelapicultor.com/blog/la-miel-y-la-temperatura/

Definition of emulsifier or emulsifying agent

Also called an emulsifier and emulsifier, an emulsifier is a chemical substance or compound used to help prepare and stabilize emulsions. An emulsion is a milky-looking liquid that contains small particles or drops of another insoluble substance in suspension. This means that they are substances that prevent liquids that do not normally mix from separating into phases that are easily distinguishable with the naked eye.

Emulsions are very common in different areas of daily life, as well as in chemistry, biology and other sciences. Many food products that we consume every day are emulsions. Some common examples are milk, ice cream, mayonnaise, mustard, and vinaigrettes.

Ice cream needs an emulsifier so the fat doesn't separate from the water.

On the other hand, many paints are also emulsions between water, oils and inorganic pigments. All of these emulsions require the addition of an emulsifying agent to maintain stability. If not, they will eventually separate into two different phases.

The term emulsifier comes from the Latin emulsus which, depending on the context, can be understood as milked or mixed. This refers to the fact that milk is an emulsion of water and fat with dissolved proteins and sugars and also to the fact that emulsions are stable mixtures of immiscible liquids.

Types of emulsifying agents

Emulsifiers can be classified according to three main criteria:

  • According to its electrical charge in aqueous media.
  • According to its solubility or hydrophilic/lipophilic balance
  • According to the functional groups they contain.

Types of emulsifiers according to their electrical charge in aqueous media

When dissolved in water, emulsifiers can ionize giving rise to four different types of chemical species:

  • Cationic emulsifiers: these are those that acquire a positive charge when dissolved in water. These emulsifiers are effective at acidic pH but are not good in solutions with high salt concentrations, since the negative ions of the salt tend to counteract the positive charge of the emulsifier, limiting its effectiveness.
  • Anionic emulsifiers: they are very common. They form negatively charged ions and are particularly useful in solutions with alkaline pH. They are also not effective in media with a high salt content for the same reasons as cationics.
  • Non-ionic or neutral emulsifiers: as their name indicates, they do not form ions when dissolved in water. Their effectiveness is not affected by pH, the presence of salts or the presence of other emulsifying agents, which is why they are some of the most widely used in the industry, including popular emulsifiers such as mono- and diglycerides.
  • Amphoteric emulsifiers: these can have both a positive and a negative charge in aqueous solution, which makes them useful in a wide range of pH values, with the exception of the pH corresponding to its isoelectric point. Soy lecithin is one of the most popular.

Types of emulsifiers according to their solubility or hydrophilic/lipophilic balance

Emulsifiers can be classified according to a scale that indicates how water-soluble or fat-soluble they are. This scale, called hydrophilic/lipophilic balance (HLB), goes from zero (0) to around twenty (20) and allows, in turn, to classify emulsifying agents into two large groups:

  • Hydrophilic emulsifiers: They have an HLB between 10-18, so they are much more soluble in water than in oil. For this reason, the greatest interaction occurs with the aqueous phase, reducing its surface tension to almost 0, which facilitates the formation of oil-in-water emulsions in which water is the continuous phase and oil is dispersed in it. in the form of small drops.
  • Lipophilic emulsifiers: they are just the opposite of hydrophilic ones. They usually have an HLB between 3 and 6 and are therefore more soluble in oil than in water. They are used to prepare water-dispersed-oil emulsions.

Types of emulsifiers according to the functional groups they contain

There is a very wide variety of emulsifiers with different compositions and structures and for different applications. In the food industry alone, more than 14 families of emulsifiers can be distinguished according to the functional group they contain, among which polysorbates, monoglycerides, diglycerides, etc. can be mentioned.

How do emulsifiers work?

Emulsifiers are amphiphilic molecules, which means that one part of the molecule (the polar or ionic end of the molecule) is hydrophilic (soluble in water), while the other part is hydrophobic or, what is the same, lipophilic ( fat soluble). This allows emulsifiers to interact with water and fats and oils at the same time, so it is always located at the interface between the two.

Action of an emulsifier on an oil-in-water emulsion Action of an emulsifier on an oil-in-water emulsion Action of an emulsifier on a water-in-oil emulsion Action of an emulsifier on a water-in-oil emulsion

The net effect is that the emulsifying agents are able to lower the surface tension at the interface of the two immiscible liquids, allowing the formation of smaller droplets of the dispersed phase within the continuous phase. Simply put, the emulsifier facilitates the initial formation of the emulsion.

In addition to this, the emulsifier also helps to keep the emulsion stable. It does this by preventing the small droplets from coalescing through coalescence to form larger droplets that ultimately coalesce to permanently separate the two phases and thus break the emulsion.

The way emulsifiers achieve this depends on the type of emulsifier. In the case of ionics (cationic or anionic), this is achieved by electrostatic repulsion between dispersed phase droplets that are covered by a layer of equally charged molecules. In other cases, coalescence is prevented by steric hindrance of the emulsifier molecules that does not allow the liquid of one drop to come into contact with that of another in order to fuse. Finally, there are cases in which a layer of water molecules firmly attached to the emulsifier layer is formed, which also makes it difficult for two nearby droplets to merge.

Examples of emulsifiers

Name Applications Soy lecithin It is used in baked goods, in the production of chocolate and margarine, among others. didecyldimethylammonium chloride Cationic surfactant commonly used in cosmetic products such as shampoos and creams. Yolk It is used to emulsify water and oil in the preparation of mayonnaise. Polysorbate 80 It is an edible emulsifier used in the preparation of ice creams, glazes, and frying oil.

References

Miller, R. (2016). Emulsifiers: Types and Uses. Encyclopedia of Food and Health, 498–502. https://www.researchgate.net/publication/301702384_Emulsifiers_Types_and_Uses

Everything in Polymers (July 24, 2020). Emulsifiers. Recovered from https://todoenpolimeros.com/2020/07/24/emulsificantes/

What is an emulsion? Definition and examples

When two or more materials are mixed we can obtain different products, one of them is the emulsion.

emulsion definition

An emulsion is a colloid of two or more liquids that cannot be mixed. In an emulsion, one liquid contains small particles or droplets of the other liquids in suspension. In other words, an emulsion is a special type of mixture that is made by combining two liquids that do not normally mix. The word emulsion comes from a Latin word meaning “to milk” (milk is an example of an emulsion of fat and water). The process of turning a liquid mixture into an emulsion is called emulsification .

Emulsions: key facts

  • An emulsion is a type of colloid formed by combining two liquids that do not normally mix.
  • In an emulsion, one liquid contains a dispersion of the other liquid, usually in the form of droplets.
  • Common examples include egg yolk, butter, and mayonnaise emulsions.
  • The process of mixing liquids to form an emulsion is called emulsification.
  • Although their component liquids may be clear, emulsions appear cloudy or milky in appearance because light is scattered by particles suspended in the mixture.

Examples of emulsions

  • Mixtures of oil and water are emulsions if we shake them in the same container. The oil will form beads and be dispersed by the water.
  • Egg yolk is an emulsion that contains the emulsifying agent lecithin.
  • The crema that forms on the surface of the espresso is an emulsion of coffee oil and water.
  • Butter is an emulsion of water and fat.
  • Mayonnaise is an oil-in-water emulsion that is stabilized by lecithin from egg yolk.
  • The photosensitive side of photographic film is coated with a gelatin silver halide emulsion to protect it.

Emulsion properties

Emulsions generally appear cloudy or white because light is scattered between the mix components. If all the light is scattered equally, the emulsion appears white. Diluted emulsions may appear slightly blue because low wavelength light is more scattered. This is known as the Tyndall effect. It is frequently seen in skim milk. If the particle size of the droplets is less than 100 nm (a microemulsion or nanoemulsion), the mixture may be translucent.

Because emulsions are liquids that do not have a static internal structure, the droplets are distributed more or less evenly through a matrix of liquid called the dispersion medium . Two liquids can form different types of emulsions. For example, oil and water can form an oil-in-water emulsion, where the oil droplets are dispersed in the water; or they can form a water-in-oil emulsion, with water dispersed in the oil.

Most emulsions are unstable, as they contain components that do not mix on their own or remain suspended indefinitely.

Definition of emulsifier

The substance that stabilizes an emulsion is called an emulsifier , emulsifier or emulsifier . Emulsifiers work by increasing the kinetic stability of a mixture. Surfactants or surface active agents are a type of emulsifiers. Detergents are an example of a surfactant. Other examples of emulsifiers include lecithin, mustard, soy lecithin, sodium phosphates, diacetyl tartaric ester monoglyceride (DATEM), and sodium stearoyl lactylate.

Difference Between Colloid and Emulsion

Sometimes the terms “colloid” and “emulsion” are used interchangeably, but the term emulsion is only appropriate when the two agents in a mixture are liquids. The difference is that the particles in a colloid can be in any state of matter. Therefore, an emulsion is a type of colloid, but not all colloids are emulsions.

How emulsification works

There are few mechanisms that may be involved in the emulsion:

  • Emulsification can occur when the interfacial surface tension between two liquids is reduced, for example with the use of surfactants.
  • An emulsifier can form a film over a phase in a mixture to form globules that repel each other, allowing them to remain evenly dispersed or suspended.
  • Certain emulsifiers increase the viscosity of the medium, making it easier for the globules to remain suspended.

Sources

  • IUPAC (2019). Compendium of Chemical Terminology . Available at: https://goldbook.iupac.org/
  • Ramos, N. and De Pauli, C. (1999). Study of the effect of incorporating emulsifiers and hydrocolloids in mayonnaise emulsion . Technological Information Center.

What is a branched alkane?

Branched alkanes constitute a class of open-chain saturated aliphatic hydrocarbons. In them, the carbon atoms are not attached one after the other in a straight line, but side chains are formed that diverge from the main chain. These side chains are called ramifications since these compounds resemble a tree that has a main trunk and branches that grow to the sides.

These compounds are actually isomers of linear alkanes, since they share the same molecular formula, C n H 2n+2 , where n represents the number of carbons in the structure.

As they are saturated hydrocarbons , branched alkanes are made up of only carbon and hydrogen. In addition, all the carbons that are part of the structure of branched alkanes have four atoms directly linked by means of simple covalent bonds. These carbons also exhibit sp 3 hybridization , as well as the characteristic tetrahedral structure of this type of hybridization.

Branched alkanes can be seen as linear alkanes, in which some of the hydrogens of the methylene chain (-CH 2 -) between the two carbon ends have been replaced by other chains of carbon atoms.

IUPAC nomenclature of branched alkanes

The nomenclature of all organic compounds, including branched alkanes, is based on the nomenclature of linear alkanes. In the construction of the names of these compounds, the main chain is named as if it were a linear alkane, while the branches are named as alkyl groups derived from the respective linear alkanes by the loss of a hydrogen.

The nomenclature of these compounds is carried out through the following steps:

  1. Select and name the main chain of the compound.
  2. Number the main chain.
  3. Identify and name all branches and order them alphabetically.
  4. Build the name.

Each step follows a specific set of rules that seek to avoid any confusion, such as two different compounds having the same name or the same compound being able to be named in more than one way.

1. Selection of the main chain

The first step is to select the longest possible chain of carbon atoms in the structure, since this will be the chain that will serve as the “trunk” or main chain of our compound, and, therefore, will provide the general name for the compound. same. To select the main chain, the following criteria are followed, in order of priority:

  1. The longest possible carbon chain is selected.
  2. If there are two or more equally long chains, the most branched (the one with the largest number of substituents) is selected.
  3. If there is more than one chain with the same number of substituents, both chains are numbered and the one with the lowest combination of locating numbers for the different branches is chosen (for numbering rules, see the instructions for step 2 below). .
  4. If there are two or more strings with the same numbering, the one that gives the lowest locants to the branches in alphabetical order is selected.
  5. If there is more than one string that satisfies all of the above, then any of them can be selected, as it will produce the same name.

Once the main chain is selected, it must be named following the IUPAC recommendations. These recommendations consist of using a prefix that represents the number of carbons in the structure, to which is added the suffix _ane that identifies the type of compound as an alkane.

The following table shows some examples of the names of the main chains of the simplest alkanes.

#C condensed formula Alkane name 1 CH 4 Methane two CH 3 -CH 3 ethane 3 CH3 – CH2 – CH3 _ Propane 4 CH 3 -CH 2 -CH 2 -CH 3 Butane 5 CH 3 -CH 2 -CH 2 -CH 2 -CH 3 pentane 6 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 hexane 7 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 heptane 8 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 Octane 9 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 Nonane 10 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 Dean 18 CH 3 (CH 2 ) 16 CH 3 octadecan … … …

2. Number the main chain

The numbering consists of assigning a number from 1 onwards to the carbon atoms of the main chain, starting at one of the two ends and ending at the other. The purpose of the numbering is to be able to unequivocally identify the carbon of the main chain to which each branch or substituent is linked. That is, these numbers allow each branch to be located or located, which is why they are called locators.

There are only two possible numbers and the choice of one or the other is carried out following a series of criteria in order of priority:

  1. The numbering that provides the smallest combination of locants is selected, regardless of the branches that appear in each locator. For example, if in a chain that has 4 branches, one of the numberings gives the numbers 3,3,4,5 as locators while the other gives 2,3,4,4, then the second one is selected since 2344 is a number less than 3345.
  2. If two numberings give the same set of locants, the one that gives priority to the branch that appears first in alphabetical order is selected (for rules for naming branches, see the next step). Thus, if the branch that appears first in alphabetical order is an ethyl and one numbering assigns this branch the locant 5 and the other assigns the locant 6, then the first numbering is used. If the first substituent in alphabetical order does not allow us to decide (because both numbers give the same locant), then we go to the next one in alphabetical order, and so on until a difference is found.
  3. If all branches in alphabetical order get the same locants regardless of which numbering is chosen, then it doesn’t matter which of the two numberings is used.

3. Identify and name all branches and order them alphabetically.

After identifying and numbering the main chain, it is easy to identify the branches, since these correspond to all the carbon chains that protrude from the main chain. The name of these branches (called alkyl groups) is constructed by replacing the ending _ane of the alkane with the same number of carbons by the suffix _yl which identifies it as an alkyl branch or radical.

The following table summarizes some of the linear alkanes that are used as the basis for the nomenclature of branched alkanes, as well as the names and structures of the respective linear alkyl radicals.

#C Condensed formula of the alkyl radical rental name 1 –CH 3 n-methyl two –CH 2 -CH 3 n-ethyl 3 – CH 2 -CH 2 -CH 3 n-propyl 4 – CH 2 -CH 2 -CH 2 -CH 3 n-butyl 5 – CH 2 -CH 2 -CH 2 -CH 2 -CH 3 n-pentyl 6 – CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 n-hexyl 7 – CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 n-heptyl 8 – CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 n-octyl 9 – CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 n-nonyl 10 – CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 n-decyl 18 – CH 2 (CH 2 ) 16 CH 3 n-octadecyl … … …

The structures of some of these alkyls and of the alkanes from which they come are shown in lineoangular form in the following figure.

branched alkane

In addition to these linear alkyl groups, there are also radicals or branches that are themselves branched. Some of these radicals receive common names thanks to their frequent occurrence in hundreds of organic compounds. The following figure shows the representation of the structure in linear angular form of some of these alkyl radicals.

branched alkane

4. Build the name.

Once the three previous steps are completed, we proceed to build the name of the branched alkane. This is done by following the steps below:

  1. The locator (or locants, if there are more than one) of the first branch is written in alphabetical order. If there are several equal branches, a locator is placed for each branch of that type that the compound has, separating each one with a comma (,). If there is more than one repeating branch on the same carbon, the locant is repeated.
  2. A hyphen is added after the last locant and the branch name is written, removing the letter o from the end of the alkyl (for example, methyl is written instead of methyl). If this ramification is repeated in the structure, a Greek prefix is ​​added to this name that indicates how many times it appears (di, tri, tetra, penta, etc.). For example, if there are two methyls, write dimethyl.
  3. If there are more branches, another hyphen is added and the previous two steps are repeated with the second one in alphabetical order and continue until the last branch is reached.
  4. When all the branches have been named, the name of the main chain is written without separating it from the name of the last branch. That is, neither a space nor a hyphen is placed.

Example

Suppose we want to name the following compound:

branched alkane

After following the steps above, we get the following:

branched alkane

Importance of branched alkanes

Branched alkanes are chemically inert compounds and very stable at high temperatures, which is why they are often used as components of many engine lubricants. In addition, its physical properties can be modified depending on the number and length of the branches, so mixtures with different degrees of fluidity, boiling points and other properties can be prepared.

On the other hand, like most organic compounds, branched alkanes are combustible substances that can be used to produce energy. Gasoline and other fuels such as diesel and kerosene contain large amounts of these types of alkanes mixed with other important organic compounds.

Even the paraffin from which most candles are made contains significant amounts of long-chain branched alkanes, making them solid at room temperature.

On the other hand, there are many saturated aliphatic polymers that consist of very long chains of carbon atoms with a series of branches that tend to appear uniformly distributed throughout the structure. In this sense, plastics as important as polypropylene or PP can be classified as branched alkanes.

Physical properties of branched alkanes

Solubility

Alkanes in general (both linear and branched and cycloalkanes) are saturated aliphatic hydrocarbons in which all of their atoms are linked together by nonpolar or pure covalent bonds. This makes them nonpolar and hydrophobic compounds , so they are completely insoluble in water.

On the other hand, they are soluble in many nonpolar organic solvents, as well as in some long-chain fats.

Boiling point

Being nonpolar molecules, the only intermolecular forces of interaction present in branched alkanes are the weak van der Waals interactions, in particular, the London dispersion forces. These forces depend mainly on the area or contact surface between two molecules.

Compared to linear alkanes, branched alkanes are characterized by having a more spherical and compact structure. This reduces the contact surface between the molecules and therefore the intermolecular forces of attraction. As a consequence, the boiling points of branched alkanes will always be lower than those of their linear isomers with the same molecular formula (and therefore the same molecular weight).

For example, the boiling point of isooctane is 99°C, while that of n-octane (which is linear) is 125.6°C.

Melting point

Like the boiling point, the melting point varies depending on the strength of the intermolecular interactions. For the same reasons cited above, branched alkanes tend to have lower melting points than linear ones.

Examples of branched alkanes

There are countless branched alkanes that exist. Some common examples are:

  • Isooctane or 2,2,4-trimethylpentane, which is one of the components of gasoline.
  • Isobutane or methylpropane, which is used as a raw material in the petrochemical industry.
  • 3-ethyl-4-methylnonane.
  • 6,7-bis(1-isopropylbutyl)pentadecane.
  • Polypropylene, which is a polymer consisting of a long chain of thousands of carbons that have a methyl group for every two carbons in the main chain.

References

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