Chemistry

(B) Valency :
Valency of an element is the combining capacity of the atoms of the element with atoms of the same or different elements.
Types of valency
There are two types of valency : Electrovalency and covalency. If an element combines by the loss or gain of electrons to form electrovalent compounds (or ionic compounds), its valency is known as electrovalency, and if an element combines by the sharing of electrons to form covalent compounds (or molecular compounds), its valency is known as covalency.
Electrovalency : In the formation of an electrovalent compound (or ionic compound), the number of electrons lost or gained by one atom of an element to achieve the nearest inert gas electron configuration is known as its electrovalency. The elements which lose electrons form positive ions, so they have positive electrovalency. So they have positive electrovalency. The elements which gain electrons form negative ions, so they have negative electrovalency.
Covalency : In the formation of a covalent compound the number of electrons shared by one atom of an element to achieve the nearest inert gas electron configuration is known as its covalency. If an atom shares 1 electron, its covalency will be 1.