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[muffn_enchntrss]

all right so we have our final exam for honors chemistry this wednesday, and our teacher gave us a list of what we need to know for the test. So I have a question about one thing, but I may post more if I don't know other things, just warnin ya.

So yeah-- how do you calculate valence electrons?

thanks.

Comments

[cowbert]

Use Hunds rule with orbitals to find out how many are in the last energy level.
(Ne is 1s22s22p6); therefore it has 8 valence electrons).
(Na has electrons configured as 1s12s22p63s1; therefore it has 1 valence electron).

[cowbert]

oops, typo. Na's electron configuration is really 1s22s22p63s1.

Remember, a neutral atom has the same number of electrons as protons (which is also the atomic number).

Then again I have been up for 72 hours with 8 hour of sleep, so I have some excuse for making silly typos :)

[dougs_content]

Knowing the electron config notation is only useful to someone who knows how to count along the periodic table or has access to the notations.

Your best bet is to simply look at the group (usually the Roman numerals at the top). That will tell you the number of valence electrons.

Also, with the notation, make sure you only count the electrons AFTER the closest noble-gas configuration, or you will be counting kernel electrons along with valence.