Introduction:

The valency of an element refers to its combining capacity or the number of electrons an atom of that element can gain, lose, or share to form chemical bonds with other atoms. Valency plays a crucial role in determining the chemical behavior and reactivity of elements. It is observed that the valency of an element is always a whole number. There are several reasons behind this phenomenon.

Atomic Structure:

The valency of an element is related to its electronic configuration, which is determined by the arrangement of electrons in its atomic structure. Electrons are arranged in different energy levels or shells around the nucleus of an atom. The outermost shell, known as the valence shell, plays a significant role in determining the valency of an element.

Octet Rule:

The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable configuration with eight electrons in their valence shell (except for the first shell, which can accommodate a maximum of two electrons). This stability is similar to the noble gases, which have a complete octet in their valence shell and are highly stable and unreactive.

Electron Configuration and Valency:

The valency of an element is determined by the number of electrons in its valence shell. Elements in the same group of the periodic table have similar outer electron configurations, leading to similar valencies. For example, all elements in Group 1 (alkali metals) have one electron in their outermost shell and thus exhibit a valency of +1. Similarly, elements in Group 17 (halogens) have seven electrons in their valence shell and generally exhibit a valency of -1.

Electron Gain or Loss:

To achieve a stable configuration, atoms tend to either gain or lose electrons. When an atom loses electrons, its valency is positive (equal to the number of electrons lost), while gaining electrons results in a negative valency (equal to the number of electrons gained). These valencies are always whole numbers because electrons are indivisible particles.

Conclusion:

The valency of an element is a whole number because it is based on the number of electrons gained, lost, or shared to achieve a stable electron configuration. The octet rule and the electron arrangement in different energy levels determine the valency. By understanding the valency of elements, scientists can predict their chemical behavior and interactions, which is crucial in various fields such as medicine, industry, and environmental sciences.

Because valncey of atom means, no. of electron in outer most orbit and electron can not be mixed in no.