A real simple way to look at ionic bonding is through Lewis dot diagrams or Lewis structures. Let's show how an adm of sodium and an adm of chlorine will combine to form the ionic compound sodium chloride. A Lewis dot diagram is just a simple way to show valence electrons. So for sodium, sodium is in group one that has one valence electron. Chlorine is a halogen and group seven has seven valence electrons, so you would just draw seven dots around chlorine. Sodium wants to satisfy an octet, and chlorine wants to satisfy an octet. With just one valence electron, sodium has a choice. It could lose its one valence electron, and as a metal, that's what it tends to do. Or it could gain seven valence electrons, which is unlikely. Combining with seven valence electrons, much rather just gain one valence electron to form its octet, then have to lose all seven. What happens is that the sodium takes its valence electron and gives it up, it loses it, and chlorine gains the valence electron. So as a result, your sodium no longer has any valence electrons. Now for Lewis diagrams, when you have an ion, we generally put it in brackets and put the charge on the outside. Chlorine now has eight valence electrons to seven it started with, and then the eighth one, it's gained from the sodium. And now it also has a charge, and it has a negative charge. The positive and negative charge is stick together forming an ionic bond. What you don't want to do is you don't want to do something like this, where you draw the sodium bonded to a chlorine in this fashion. This symbol that we use right here, this dash line, is indicative of a covalent bond, that the electrons are being shared back and forth between the sodium and the chlorine. And that's not what happens here. The sodium is losing an electron, the chlorine is gaining the electron, and they bond together because of their opposite charges, not because of a covalent bond. Let's do the process again, but this time let's show how potassium and oxygen will form potassium oxide. Just like before we can start with the metal, and potassium is also an alkali metal, so like sodium it has one valence electron. Oxygen is in group six. So it only has six valence electrons. Potassium is a metal, we'll give up its electron, and that will stabilize itself. The problem is that oxygen now only has seven electrons, so it hasn't satisfied its octet. What we need is we need another potassium atom. It too can give up an electron to oxygen, and the result is that we will now have two potassium each with a positive charge. My oxygen, which started out with six valence electrons, has picked one up from this potassium and one up from this potassium. Now as a result, as a two negative charge, we're not going to show covalent bonding, we're just going to leave these opposite charges to attract each other. And that's why potassium oxide has a formula of K2O. You need two potassium to satisfy the octet rule for oxygen.