Valency and valence electrons are related concepts in chemistry, but they refer to different aspects of an atom or molecule.
Valence Electrons: Valence electrons are the electrons located in the outermost energy level or shell of an atom. These are the electrons involved in chemical bonding and determining the atom's chemical properties. The number of valence electrons influences an atom's reactivity and its ability to form bonds with other atoms.
Valency: Valency, on the other hand, is a measure of an element's combining power or its ability to bond with other elements. It represents the number of electrons an atom of an element can gain, lose, or share when it forms chemical compounds. Valency is typically determined by the number of valence electrons an atom possesses.
In simpler terms, valence electrons are the electrons found in the outermost shell of an atom, while valency refers to the number of electrons an atom can gain, lose, or share to form chemical bonds.
For example, oxygen has 6 valence electrons (two in its first shell and four in its outermost shell). Oxygen's valency is 2 because it tends to gain or share two electrons to complete its outer shell and achieve stability. Similarly, sodium has one valence electron and a valency of 1 since it easily loses this electron to achieve a stable electron configuration.
Valence electrons and valency are important concepts in understanding chemical bonding and the formation of chemical compounds.