We’ve briefly looked at the idea of ionization and what ions are. Now let’s look at those topics more deeply, so we can better understand not only the underlying process, but how this process affects the formation of chemical compounds and molecules. First, let’s review a little bit about what ions actually are.

Ions are atoms with an unequal number of protons and electrons, like the one shown there to the right. If there are more protons than electrons, as in this example, then it’s a positive ion, what we call a cation. If there are more electrons than protons, then it’s a negative ion, what we call an anion. The process of gaining and losing electrons occurs in a region called the valence shell, and we’ll get into that a little bit more later, but first, let’s work on notation.

Ions are written based on the element and the net charge. So, to use the example from before, we have an element with four protons – that defines it as beryllium – and two electrons. The four protons give it a plus-4 charge, the two electrons give it a minus-2 charge, for a net charge of positive 2. So, to write

this ion’s name, we would write it as beryllium 2-plus, the 2-plus representing the net charge.

Let’s look at one other example. Because of the nine protons, we know that this is fluorine, but it has 10 electrons. So the nine protons give it a positive 9 charge, the ten electrons give it a negative 10 charge, giving it a net charge of negative 1. So we would write this a fluorine 1-minus, or, if you want to just drop the one, you can just write this as fluorine-minus.

We mentioned before that the gaining and losing of electrons occurs in the valence shell. Let’s look at what that is. For s- and p-block elements, valence shell electrons are the electrons with the highest principal number. These electrons participate in ionization and chemical reactions. Fortunately, for s- and p-block elements, which are often called main group elements, it’s very easy to figure out how many valence electrons they have, because it just goes from left to right, increasing from 1 to 8. And, again, this does not apply to f- and d-block elements, for whom figuring out the number of valence electrons is a much more complicated task.

The end goal of the process of ionization is to get what we would call a stable configuration. The most stable electron configuration have a full outer valence shell. These are noble gas configurations. For example, helium has 2 electrons, because its valence shell can only hold two electrons. Neon’s valence shell has 8 electrons, because that’s how many its outermost shell can hold. Argon also has 8 electrons in its outermost shell. These are the electron arrangements that most elements are trying to get to.

Now let’s look at the different types of ions, and how they achieve these electron configurations. First, let’s look at cations. As a reminder, cations have a positive charge, that is they have more protons than

electrons. This occurs when a neutral atoms loses electrons. Most elements, and indeed pretty much all metals, form cations. It’s not always obvious what charge an ion for a given element will form, but for the first three groups, it is always consistent. For group 1, they will always form 1-plus ions, group 2 will always for 2-plus, and group 3 will always form 3-plus.

Let’s look at an example of cation formation. For our example, let’s look at magnesium, element 12. Because it has 12 protons, neutral magnesium also has 12 electrons: 2 in its inner-shell, 8 in the next shell, and 2 in its outer shell. So in order to get a full valence shell, it must either lose 2 electrons or gain

6 electrons. But it is way, way easier to lose 2 electrons than it is to gain 6 electrons. And that’s exactly what magnesium does, is it loses those two outer electrons to become magnesium-2-plus, because now it has 12 protons and 10 electrons for a net charge of 2-plus.

Now let’s look at how this process occurs with anions. Again, as a reminder, anions have a negative charge, that is more electrons than protons. This occurs when a neutral atom gains electrons. Very few elements actually form anions, only some elements from groups 15, 16, and 17. That said, that doesn’t mean that these are unimportant. These are extremely important. Even just look at the elements themselves: nitrogen, oxygen, fluorine, chlorine. These form extremely important compounds. And it’s always easy to tell what the charge is going to be on an anion. For group 17 elements, they form 1- minus ions, for group 16, they form 2-minus, and for group 15, they form 3-minus.

Let’s look at an example. For our example, let’s look at element 9, fluorine. Neutral fluorine has 9 electrons. But in order to get a full valence shell, it either has to gain 1 electron or lose 7 electrons. And obviously, it is way easier to gain 1 than to lose 7, and that’s exactly what fluorine does. It gains 1 electron to become fluorine 1-minus, or fluorine minus.