What are the keypoints involved in ionic bonding?

First, work out where the electron transfer is going to happen. Because it's ionic bonding we know 1 atom will lose electrons, and 1 will gain them. By using the electron shell's magic numbers of 2,8,8.. and drawing the outer shell like this we then see which is losing the electrons and which is gaining them (and how many they will lose or gain) to get to the magic number. As electrons are negatively charged, the atom that gains them becomes a negative ion, and the atom that loses electrons becomes a positive ion as its lost some negative charge. If an atom loses 1 electron, it becomes a 1- ion, if it loses 2 electrons, it becomes a 2- ion and so on. Now that we have positive and negatively charged ions, the 2 opposite charges will attract and so we have our bond. Remember, if you have an atom that loses only 1 electron, and another needs to gain 2, you're going to need 2 atoms to give away enough electrons - here you would use an example such as sulfur and potassium to make it clearer. So in summary: using electron shells, work out which atom has too many electrons and which one doesn't have enough state which atom is transferring electrons and which is gaining them, and how many the number of electrons gained or lost causes the ions charge the 2 opposite charges attract each other in a bond