WHAT IS CHEMICAL PERIODICITY? MAIN FEATURES - CHEMISTRY - 2024

The chemical periodicity or regularity of the chemical properties is the regular variation, recurrent and predictable chemical properties of the elements when the atomic number increases.

Thus, chemical periodicity is the basis for a classification of all chemical elements based on their atomic numbers and chemical properties.

The visual representation of chemical periodicity is known as the periodic table, Mendeleïev's table, or periodic classification of elements.

This shows all the chemical elements, arranged in increasing order of their atomic numbers and organized according to their electronic configuration. Its structure reflects the fact that the properties of chemical elements are a periodic function of their atomic number.

This periodicity has been very useful, since it has allowed us to predict some properties of elements that would occupy empty places in the table before they were discovered.

The general structure of the periodic table is an arrangement of rows and columns in which the elements are arranged in increasing order of atomic numbers.

There are a large number of periodic properties. Among the most important are the effective nuclear charge, related to the atomic size and tendency to form ions, and the atomic radius, which influences the density, melting point and boiling point.

Ionic radius (affects the physical and chemical properties of an ionic compound), ionization potential, electronegativity and electronic affinity, among others, are also fundamental properties.

The 4 main periodic properties

Atomic radio

It refers to a measure related to the dimensions of the atom and corresponds to half the distance that exists between the centers of two atoms that are making contact.

As you travel through a group of chemical elements in the periodic table from top to bottom, the atoms tend to get larger, as the outermost electrons occupy energy levels farther from the nucleus.

This is why it is said that the atomic radius increases with the period (from top to bottom).

On the contrary, going from left to right in the same period of the table increases the number of protons and electrons, which means that the electric charge increases and, therefore, the force of attraction. This tends to decrease the size of the atoms.

Ionization energy

This is the energy it takes to remove an electron from a neutral atom.

When a group of chemical elements in the periodic table is traversed from top to bottom, the electrons of the last level will be attracted to the nucleus by a smaller and smaller electrical force since they are being further away from the nucleus that attracts them.

That is why it is said that the ionization energy increases with the group and decreases with the period.

Electronegativity

This concept refers to the force with which an atom generates attraction towards those electrons that make up a chemical bond.

Electronegativity increases from left to right over a period and coincides with the decrease in metallic character.

In a group the electronegativity decreases with increasing atomic number and increasing metallic character.

The most electronegative elements are located in the upper right part of the periodic table, and the least electronegative ones in the lower left part of the table.

Electronic affinity

Electronic affinity corresponds to the energy that is released at the moment in which a neutral atom takes an electron with which it forms a negative ion.

This tendency to accept electrons decreases from top to bottom in a group, and becomes greater as you move to the right by one period.

Organization of the elements in the periodic table

An element is placed in the periodic table according to its atomic number (number of protons that each atom of that element has) and the type of sublevel in which the last electron is located.

In the columns of the table are the groups or families of elements. These have similar physical and chemical properties and contain the same number of electrons in their outermost energy level.

Currently, the periodic table consists of 18 groups each represented by a letter (A or B) and a Roman number.

The elements of the groups A are known as representative and those of the groups B are called transition elements.

There are also two sets of 14 elements: the so-called "rare earths" or internal transition, also known as the lanthanide and actinide series.

The periods are in the rows (horizontal lines) and are 7. The elements in each period have the same number of orbitals in common.

However, unlike what happens in the groups of the periodic table, the chemical elements in the same period do not have similar properties.

The elements are grouped into four sets according to the orbital where the electron with the highest energy is located: s, p, d and f.

Element families or groups

Group 1 (alkali metal family)

Everyone has an electron at their ultimate energy level. These form alkaline solutions when they react with water; hence its name.

The elements that make up this group are potassium, sodium, rubidium, lithium, francium and cesium.

Group 2 (alkaline earth metal family)

They contain two electrons in the last energy level. Magnesium, beryllium, calcium, strontium, radium, and barium belong to this family.

Groups 3 to 12 (family of transition metals)

They are small atoms. They are solid at room temperature, except for mercury. In this group, iron, copper, silver and gold stand out.

Group 13

Metallic, non-metallic and semi-metallic elements participate in this group. It is made up of gallium, boron, indium, thallium and aluminum.

Group 14

Carbon belongs to this group, a fundamental element for life. It is made up of semi-metallic, metallic and non-metallic elements.

In addition to carbon, tin, lead, silicon and germanium are also part of this group.

Group 15

It is made up of nitrogen, which is the gas with the highest presence in the air, as well as arsenic, phosphorus, bismuth and antimony.

Group 16

In this group is oxygen and also selenium, sulfur, polonium and tellurium.

Group 17 (family of halogens, from the Greek "salt-forming")

They have the facility to capture electrons and are nonmetals. This group is made up of bromine, astatine, chlorine, iodine and fluorine.

Group 18 (noble gases)

They are the most stable chemical elements, since they are chemically inert since their atoms are filled with the last layer of electrons. They are little present in the Earth's atmosphere, with the exception of helium.

Finally, the last two rows outside the table correspond to the so-called rare earths, lanthanides and actinides.

References

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