Lithium Nitride -> Li3N? Li2N?

Question

When given a compound named Lithium Nitride, how do you know whether or not it is Li3N or Li2N, etc. without a periodic table?

HELP PL0x!!!!!!!!!!!!11

Answer 1

Li has an oxidation number of 1+

N has an oxidation number of 3-

That means for every N, you need 3 Li's to make up for the oxidation number

You can also do this with formal charge, although im not sure if you've covered formal charge yet.

btw it's Li3N if you didn't catch it. just making sure =]

Answer 2

Can you determine the oxidation states without looking at a periodic table, not really. Lithium (Li+) nitride(N3-) is Li3N.

Tips for finding oxidation states. The oxidation states is basically the charge of the atom would have if its shared electrons were held completely by the atom that attracts them more strongly.

For example in CH4 C is the attract electrons the strongest.

There are 8 shared electrons and that's 4 more electrons than carbon in its natural state, so carbon has a oxidation state of 4-.

You just have to memorize oxidation states. Group 1 compounds (like Li) have oxidation states of +1. Group 2 compounds +2. The main ones are hydrogen 1+ and oxygen which usually has a oxidation state of 2- of 1- in peroxide. Also remember the charge on common polyatomic ions like SO42- and NO3-.