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Every element has some capacity to join or combine with other elements. The capacity of the element for joining or combining is called valency of that element.

i. The valency of the element is always a whole number.

ii. For example,

The atomic number of sodium = 11

The electronic configuration of ₁₁Na= 2,8,1

The atomic number of potassium = 19

The electronic configuration of ₁₉K = 2,8,8,1

Hence, sodium and potassium have a same valency (electrons in the outermost shell) of 1.