Chlorine usually needs one electron and is satisfied. Like phosphorous and sulfur.
Cl is dealing with oxygen, it may well end up unsatisfied. Think instead in terms of how many valence electrons Cl has and how it can use them.
Simply think about it like this: for every O you want to end up neutral (talking formal charges), give it a double bond with the Cl, and for the O you want to end up with the -1 formal charge give it a single bond. So for ClO-, Cl has 3 lone pairs and a single bond to O; for ClO
2-
, Cl has 2 lone pairs, a double bond to an O and a single bond to an O (bent,v-shaped geometry, right?); ClO
3- has 1 lone pair, 2 double bonds to O and a single bond to another O, so it will have pyramidal geometry. What about ClO
4-?