how to remember valency of an element?
When we move from left to right in periodic table valency increases. But after 4, it decreases 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 aluminum 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.