how do you determine the number of valence electrons in an atom?

I've checked my chemistry book, but it does not mention this for some reason? 

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  • 3 weeks ago
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    You use the periodic table and an element's position in the periodic table. If you look at the main group elements (Groups 1, 2, 13, 14, 15, 16, 17 and 18), the number of valence electrons increases with each group. So, everything in group 1 and 2 have 1 and 2 valence electrons, respectively. For the other groups, Group 13 elements have 3, group 14 have 4 and so on to the noble gases which have 8 valence electrons.

    Dealing with most of the transition metals and valence electrons gets weird. 

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