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Atoms and Atomic Structure
Chemical Bonding
Particle Physics

How do you count the valence electrons of an atom?


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July 29, 2014 7:04PM

The number of valence electrons is just how many electrons an atom has in its outer shell. It's easy to figure out if you've got a periodic table.

(See the link below this answer for a good periodic table).

All the elements in each column have the same number of electrons in their outer shells. All the elements in the first column all have a single valence electron (H, Li, Na, K, etc.).

The second column elements all have 2 valence electrons (Be, Mg, Ca, Sr, etc.).

Skipping over the gap, go to the Group 3 elements, which all have 3 valence electrons (B, Al, Ga, etc.).

The elements in the next column (C, Si, Ge, etc.) all have 4 valence electrons.

The elements in the next column (N, P, As, etc.) all have, yes, you guessed it, 5 valence electrons.

O, S, Se, and the others in this column have 6 valence electrons.

The halogens in the next-to-last column (F, Cl, Br, etc.) have 7 valence electrons.

The noble gases in the right-most column (Ne, Ar, Kr, etc.) all have 8 electrons in their out except for He, which only has 2 electrons.

In column 1 all of those elements have 1 valence electron.

In column 2 there are 2 valence electrons. He(Helium) is included here.

Skip columns 3 to 12 because their valence electrons vary.

Column 13 has 3 valence electrons.

Column 14 has 4 valence electrons.

Column 15 has 5 valence electrons.

Column 16 has 6 valence electrons.

Column 17 has 7 valence electrons.

Column 18,except for He(Helium), has 8 valence electrons.