If an imaginary compound has a formula of X4Y3 then how many electrons are in the outer shell of each element?

Answer 1

If a compound has the formula X4Y3, then that means that 4 atoms of imaginary element X are combined with 3 atoms of imaginary element Y. The overall charge of the compound is neutral, and so the charges of the 4 X's and the charges on the 3 Y's must cancel out. We need to find the charge on each atom in the compound to figure out the number of electrons in the outer shell. Once we figure out the charge, finding the number of electrons is easy.

So what must the charge on each atom be for this to work out? X is written first, and so it is going to be a positive ion, which means that Y is a negative ion. If you try some different combinations of +1 or +2 ions with -1 or -2 ions, you'll find it doesn't work out right -- there is always a net charge on the final compound when you combine them in a 4 to 3 ratio. The only way it works out is this:

If X has a charge of +3 and Y has a charge of -4.

Now if X has a charge of +3, it must have lost 3 electrons, which means that it has 3 electrons more than a stable octet. That means X has 3 valence electrons (3 + 0 = 3).

If Y has a charge of -4, it has gained 4 electrons, which means that it has 4 electrons less than a stable octet. That means that Y has 4 valence electrons (8 - 4 = 4).

See the Related Questions to the left for more information about counting electrons and the octet rule in chemistry.