Define valency by taking examples of silicon and oxygen.
The valency is the combining capacity of an atom. The number of electrons donated or accepted or shared by an atom of an element, so as to have a stable configuration of the nearest noble gas is called valency.
The valency is equal to the number of electrons in the outermost shell (valence shell) of an atom.
For example, silicon (atomic number 14) has the following electronic distribution:
K = 2, L = 8, M = 4.
In the outermost shell there are 4 electrons so, the valency of silicon is 4.
In case of oxygen (atomic number 8), the electronic distribution in various shells is given below:
K = 2, L = 6
There are six valence electrons in the atom of oxygen.
Valency of oxygen will be = 8 – 6 = 2
Valency of Chlorine
Valency of Potassium