How do I find the valence for an atom of an element?

For example, if I have CO2, what would be the valence for C?
How would I find it?

Thank you

Question

How do I find the valence for an atom of an element?

For example, if I have CO2, what would be the valence for C?
How would I find it?

Thank you

anonymous · Answer

Valence electrons is found by drawing out the Lewis structures of the element
Since carbon is in group 4, it has 4 electrons in its Lewis structure|dw:1351821700452:dw| so valance electrons on carbon is 4 (it can form 4 possible bonds)
Oxygen is in group 6, and has 6 electrons in its Lewis structure |dw:1351821725210:dw|
However, we cannot count the lone pairs as valance electrons, and thus oxygen only has 2 valance electrons (essentially means it can only form 2 bonds)