# How can I learn the valencies of the first #20# elements?

##### 1 Answer

So, the first 20 elements in the periodic table start with **H** and end with **Ca**. The quickest way to remember the number of valence electrons is to form a relationship with the number of the group the element is located in.

I'll skip noble gases, since these are elements which have a stable octet, and as a result are usually not a part of chemical reactions.

Starting with the second row:

*Group 1* - **Li** - has 1 valence electron (v.e);

*Group 2* - **Be** - has 2 v.e;

*Group 13* - **B** - has 3 v.e;

*Group 14* - **C** - has 4 v.e;

*Group 15* - **N** - has 5 v.e;

*Group 16* - **O** - has 6 v.e;

*Group 17* - **F** - has 7 v.e;

The group number jumps from 2 to 13 because the first 20 elements are not found in groups 3-12.

Then the pattern repeats itself in the third row. Again,

*Group 1* - **Na** - has 1 v.e;

*Group 2* - **Mg** - has 2 v.e;

*Group 13* - **Al** - has 3 v.e;

*Group 14* - **Si** - has 4 v.e;

and so on.

So, if you can examine a periodic table, the number of valence electrons can be determined if you look at group number.

The *digit that represents the units* (1 in 1, 3 in 13, 4 in 14, 6 in 16, and so on) is equal to the number of valence electrons.

**K** and **Ca** follow the same pattern. For row 4,

*Group 1* - **K** - has 1 v.e;

*Group 2* - **Ca** - has 2 v.e;

So, always think group number