Valence (Lat. Valentia - Strength)

Valence (from the Latin Valentia, meaning “strength”) is a chemical characteristic that indicates the number of electrons that an atom can accept or give up during the formation of chemical bonds. It plays an important role in determining the structure and properties of molecules and materials.

The concept of valence was developed in the early 20th century by scientists Lewis and Kosel. They proposed a model in which atoms strive to complete their outer shell of electrons by filling it with the most stable number of electrons. This number is usually 8 electrons, with the exception of some elements that have fewer electrons in their outer shell.

The valence of chemical elements can be determined by their positive number on the periodic table, which indicates the number of electrons in the outer shell. For example, elements of the first group (alkali) have one electron in the outer shell, so their valency is one. Elements of the second group (alkaline earth) have two electrons in the outer shell, so their valence is two.

Valency can also be determined based on the oxidation state of an atom in a compound. The oxidation state shows how many electrons an atom has lost or gained during the formation of a chemical bond. For example, in an HCl molecule, the valency of chlorine is one because it accepts one electron from the hydrogen atom.

Valence also plays an important role in determining the type and strength of chemical bonds between atoms. If atoms have the same valence, they can form a covalent bond in which they share a pair of electrons. If atoms have different valences, they can form an ionic bond in which one atom gives up an electron and the other accepts one.

In addition, valency plays an important role in plant biology. The apical meristem, the undifferentiated embryonic tissue at the tips of plant shoots and roots, has a special valence that allows it to form new cells and tissues. This ensures the growth and development of the plant.

Thus, valence is an important chemical characteristic that determines the ability of atoms to form chemical bonds. It plays an important role in chemistry, materials science and biology, and is a key factor in shaping the properties of molecules and materials.