Atoms can attach to each other

We are all different. Some of us like to hang out with a lot of friends. Others prefer to be on their own. And then there are best friends that only spend time with each other. It's the same with atoms.

Argon likes to be alone. Metal atoms, like iron, gather in huge gangs - billions of them together. While nitrogen atoms often stick close together two-by-two. But what determines how social the atoms are? It's the electrons in the outermost electron shell - the valence electrons.

If an atom has eight electrons in its valence shell - then it's content. It doesn't need to connect with anyone else. That's the case for the gas argon, for instance. Eight is like a magic number in the world of atoms. Atoms prefer to have eight valence electrons - this is what's called the octet rule.

The atoms in metals need to get rid of electrons to have eight in their outermost electron shells. When they do that, the discarded electrons whizz around, without belonging to any particular atom. That enables metal atoms to form chunks with billions of atoms. Like these iron atoms. The valence electrons act like glue, holding the metal atoms together.

Then there are atoms that need more electrons to reach the number eight in their outer shells. They can choose a different way. They form smaller units, where they share some of their valence electrons with each other. Instead of not belonging to any atom, as in metals, these shared electrons belong to both atoms. These small groups of atoms are called molecules.

A molecule can consist of two atoms, or three or four… up to several thousand. So a molecule is a small group of atoms that are attached to each other. Molecules can consist of atoms of the same element, like this nitrogen molecule, or this sulphur molecule. Or they can be made of atoms from different elements, like this water molecule. When different elements are assembled into molecules, they have formed a new compound.

Water is not a mix of oxygen and hydrogen. It's a chemical compound made of the two elements. A compound usually has completely different properties than the elements that formed it. Take sodium chloride for instance - ordinary table salt. Sodium is a corrosive metal.

Chlorine is a poisonous, corrosive gas. Put them together in a compound - and they are harmless. Some molecules are held together pretty loosely. They can easily decompose, or exchange atoms with other molecules. Other molecules are more stable.

When those atoms are joined together, they tend to stay in that molecule. Just like best friends, that stick together no matter what. Why do the atoms in argon prefer to be alone? Because they have eight electrons in their outermost shell. Why do iron atoms like to hang out with a lot of others?

Because they have kicked out some of their electrons. The free-flying electrons hold these iron atoms together like glue. Why are nitrogen atoms like two best friends, that always hang out with each other, and ignore everyone else? Because they have formed a molecule where they share some of their electrons. In all three of these cases, atoms do this because they want to have eight electrons in their outer electron shells.

That means they are content, and don't want to play with anyone else. Sorry about that, Leon!