How do you write the lewis structure for PCl3? How do you find the number of valence electrons and how do you know where to place those valence electrons as bonds or lone pairs?
What about for a species with a cation and anion like KClO4? K is a plus one cation and ClO4 is a minus one anion. Does the Cl use an expanded octet to form bonds with the oxygen atoms? What period does Cl need to be in to expand its octet?