Chemically polar amino acids have an uneven (AKA polar) distribution of electrons over their surface.
Charged amino acids have a charged ion in their structure. This is probably where my knowledge is a little shaky!
I guess I am confused at this point. Does this just mean that charged amino acids are really polar amino acids? If that is correct that would explain why I have seen histidine categorised as a charged amino acid, but has no clear ions.