Question

(a) How do we calculate the valency of an element from its electronic
configuration ?
(b) How does the valency vary in a period ?

Answer 1

Electronic configuration means arranging electrons in shells , subshells and orbitals
For example Magnesium :
Atomic number 12
electronic configuration: 1s2 2s2  2p6 3s2
valence electrons : 2
hence to attain stability magnesium will lose 2 electrons . Hence valency is 2.

so based on valence electrons valency is calculated.

b] Valency in a period:
As we move in a period from left to right in each short period of  a periodic table valency increases from 1 to 4 and then decreases to zero.
for example:
Third period : Na Mg  Al    Si    P   S   Cl Ar 
                       1    2     3     4    3    2    1  0
so elements in the same period have different valencies

Answer 2

hey mate !!!


combining capacity of an element is known as valency.



valency is calculated electronic configuration.


for example:-

sodium.


Na => 2,8,1 .


it have to lose one electron to gain stability.






so the valency of sodium will be:- Na+


that means it have one lose electron.


so the valency of sodium is be 1.




b) the valency on moving in period first increase 1 to 4.

after that it will be decreases.



and comes to be zero.



hope it helps!!!

thanks