HELP!! CHEMISTRYWhat's the most easiest explanation of valencies and how to use them?

Answer 1

The valency of an ion is basically its electrical charge. You need to use them to work out how two ions will combine into an ionic compound. The fundamental rule is to wind up with no overall charge.

So, if you have an ion with valency +2 (say Mg) and one with valency -1 (say F) then you need two lots of -1 to balance out one lot of +2, so the ionic compound is Mg F2.

For comparison, tin(IV) phosphate will have 3 lots of Sn (4+) and 4 lots of PO4 (3-) so that we have a total of +12 and -12 = 0. So the formula is Sn3(PO4)4.