define the term valency? how does it change on moving down a group? justify your answer
Answers
What do you mean by the term Valency ?
Valency of an element is defined as its combining capacity.
How does valency change on moving down a group ?
On moving down a group, the valency of elements remains the same.
Why is this so ?
This is because elements with similar properties (physical and chemical) are placed in the same group.
The properties are defined by the no. of valance electrons.
So, in a group, the no. of valance electrons is the same.
Hence, the valency is also the same.
A few Examples :
Eg 1. Group 1 - Alkaline Metals
Element Z EC Valency
Li 3 2, 1 1⁺
Na 11 2, 8 , 1 1⁺
K 19 2, 8, 8, 1 1⁺
Eg 2. Group 2 - Alkaline Earth Metals
Element Z EC Valency
Mg 12 2, 8, 2 2⁺
Ca 20 2, 8 , 8, 2 2⁺
Eg 3. Group 17 - Halogens
Element Z EC Valency
F 9 2, 7 1⁻
Cl 17 2, 8 , 7 1⁻