Physical Science:

Valency describe the combining power of an atom or a group of atoms with other atoms. It is determined by the number of electrons an atom can gain, lose or share when it reacts with another atom. The valency of an element is usually a whole number that indicates the number of electrons an atom of that element can gain or lose in order to achieve a stable configuration.

The valency of an element is determined by the number of electrons in the outermost shell of its atoms, which is also known as the valence shell. The valency of most elements can be predicted by looking at their position in the periodic table. For example, elements in Group 1 of the periodic table have a valency of 1, while elements in Group 2 have a valency of 2, and elements in Group 3 have a valency of 3. Elements in Group 15 have a valency of -3, elements in Group 16 have a valency of -2, elements in Group 17 have a valency of -1, and elements in Group 18 have a valency of 0 since they have already achieved a stable configuration. Elements in Group 14 however, have a valency of \(\pm4\) as these atoms either gain 4 electrons or lose 4 electrons in order to obtain stable configuration.

Valency is important in understanding chemical bonding and chemical reactions. For example, elements with a valency of 1 can form compounds by sharing one electron with another atom, while elements with a valency of 2 can share or lose two electrons. By knowing the valency of an element, chemists can predict the types of chemical bonds that it can form with other elements and the chemical properties of the resulting compounds.