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# How to learn the valancies of the first 20 elements?

So, the first 20 in the start with **H** and end with **Ca**. The quickest way to remember the number of 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 , 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 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 .

**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 ##->## units digit ##->## valence electrons.