how does valency vary in a period on going from left to right in modern periodic table?
Dear Student,
When we move from left to right in periodic table valency increases. But after 4, it decreses also.
The electrons present in the last shell determine the valency of a particular element.
If the number of valence electrons ≤4: valency = number of valence electrons
If the number of valence electrons >4: valency = 8 - number of valence electrons.
For e.g.
Group in periodic table | Number of valency electrons | valency |
1 | 1 | 1 |
2 | 2 | 2 |
13 | 3 | 3 |
14 | 4 | 4 |
15 | 5 | 3, 5 |
16 | 6 | 2, 6 |
17 | 7 | 1, 7 |
18 | 8 | 0, 8 |
For your convenience, I am providing two examples to show how valency of any element can be found out.
If you consider the element aluminium and try to write its electronic configuration, then it is 2, 8, 3 the valency is equal to 3.
However, for element oxygen having electronic configuration 2, 6 the valency is 8 - 6 = 2.