 Today we're going to discuss the formation of ions, and then this is going to flow into how we make ionic compounds. So the first thing we need to understand about atoms is that they have a specific number of valence electrons. Valence electrons are the electrons that are on the outermost energy level, and we can tell the number of electrons in the representative group atoms by their group number. So the representative groups are the groups that have an A, so 1A through 8A. Group 1A has one valence electron, group 2A has two, 3A has three, 4A has four. I'm sure you're seeing the pattern by now, all the way to 8A, and they have eight valence electrons. Eight valence electrons is the maximum number of electrons that you can have. That is basically a full set, which we call an octet. So the noble gases, which is the common name for the group A elements, have a full set of valence electrons. This is the most stable electron configuration to have a full set. All of the other elements want to be like a noble gas and want to achieve an octet. So they are going to gain or lose electrons so that they reach eight valence electrons. So when we talk about ions, ions are atoms that do not have an equal number of protons and electrons. If they are equal, they would be neutral, and ion has an unequal number, so they're either going to be positively charged or negatively charged. So ions, for example, group 1A. If we use sodium as an example of a group 1A element, sodium has 11 protons and 11 neutrons and a normal neutral atom. Sodium is going to lose its one valence electron so that it looks like the noble gas that precedes it. When it does this, it loses one electron. It's still going to have 11 protons, but now, oops, that's electrons, it's going to have 10 electrons. Now it is not neutral anymore. It has one extra positive charge versus negative charge. So now this would be sodium with a positive charge, positive one. So every element that's in group 1A is going to do the same thing. They are going to lose their one valence electron and it's going to give them a plus one charge. Group 2A is going to do something very similar. So it's plus one for 1A. Group 2A, if we look at magnesium as an example, 12 protons, 12 electrons, it's neutral. It wants to look like a noble gas. It's going to lose its two valence electrons, two electrons leave. We still have 12 protons, but now we only have 10 electrons. Since there are two more positives than negatives, it has a plus two charge. And we would write the symbol as magnesium, two plus. Everything in group 2A is going to do the same thing. They are going to lose their two valence electrons and form a two plus ion. Same pattern for group 3A. And it's going to form a plus three charge. Group 4A doesn't follow the pattern. In group 4A, the elements are mostly non-metals. Non-metals that have four valence electrons, the upper ones, aren't going to form ions. So they would either have to lose four electrons or they would have to gain four electrons. And that's too much energy involved. So normally we're not going to see ions here. Some of the transition metals will form plus four charges, but that doesn't apply to all of these. So we are going to just kind of put an X here and skip over that. Now the non-metals, starting group 5A over on this side, if we followed this same pattern, they would have to lose five electrons to get to eight valence electrons. Or the easier way would be to gain three. So it's easier for these guys to gain three electrons to reach eight. So if we have something like nitrogen, nitrogen for example has seven protons, seven electrons. In this case, to form an ion, it's going to gain. We're going to add three electrons. When we do that, we still have seven protons. It's still nitrogen. But now we have ten electrons. This is going to give us a full set. It's going to look like the noble gas neon, which has ten electrons. So now we have more negatives than positives. So we have a negative three charge. And you'd write the symbol like this. So the non-metals that are in group 5A are all going to do the same thing and are all going to have a negative three charge because they're going to gain three electrons. Group 6A, oxygen for example. Oxygen has eight protons, eight electrons. It's nearest noble gas. What it wants to look like is neon, which has ten electrons. So we're going to gain two electrons. So eight protons, ten electrons. It's going to have a negative two charge because it has two extra electrons. So everything, all of the non-metals in group 6A are going to do the same thing. Have a negative two charge. Group 7A, seven valence electrons. They need to gain one more to look like the nearest noble gas. So they're going to have one extra electron. They're going to have a negative one charge. Group 8A, they already have a full set of electrons. So they're not going to gain or lose. So we're not going to form any ions for group 8A. Now that you understand how the ions are formed, we can take this information and start making ionic compounds.