[dekkerje]

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How do you work out the valency of electrons?
 
I have a test soon :mad: and I need to know how to do it for each atom/element.
 
thanks!
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[Perito]

It follows from the position in the periodic table. Group 1A all have a valence of 1. Group 2A all have a valence of 2. Group 3A have valences of 3. Group 4A all have valences of 4.

After that, it goes down. Group 5A have valences of 3, Group 6A have valences of 2, Group 7A (the halogens) have valences of 1. Groups 5A, 6A, and 7A, as you go down in the table, also exhibit valences of 5, 6, and 7 respectively. Group 8 has filled shells and, therefore, has a valence of zero. Actually, some group 8 elements can form compounds, but they rarely do.

There are plenty of exceptions, especially as you go from the top down in the periodic table. Those are best simply memorized.

Group 1B, 2B, etc. follow a similar pattern but you are working with D-shell electrons so the results are somewhat different. Iron, for example, is in group 4B. It exhibits valences of 2 and 3.

Here is a Wikipedia page. There's a periodic table chart, about halfway down, that shows, in colors, the valences for all elements.

Valence (chemistry) - Wikipedia