Covalent Bonding

The last major type of bonding is covalent bonding. (It's not THE last type of bonding, mind you, because there are other random types like hydrogen bonds, but they're not important for now.)

The premise of covalent bonding is simple. Non-metal atoms get together and share electrons so that each can have a full outer shell. The atoms are bonded together by the electrostatic forces between the nuclei of the atoms and the shared electrons. Since sharing is caring and 1 + 1 = 3, covalent bonds are seriously strong bonds.

The number of covalent bonds an atom will make is influenced by its place on the periodic table. For example, group 14 elements like carbon and silicon tend to make 4 covalent bonds, group 15 elements like nitrogen tend to make 3 covalent bonds, and so on.

Many covalently bonded substances exist in molecules and are therefore known as covalent molecular substances. Some examples of this include carbon dioxide, oxygen, ozone and water. These molecules are held together by very strong covalent bonds, but the molecules in turn are bonded to each other by very weak intermolecular forces. It is due to the weakness of these intermolecular forces that the boiling and melting points are relatively low and hence there are lots of covalent molecular compounds that exist as gases, such as oxygen, nitrogen and methane gas.

Another effect of the weak intermolecular forces is that covalent molecular substances tend to be relatively soft. Correct me if I'm wrong on this, but I think that it's because the molecules aren't that tightly packed together because the intermolecular forces are so weak. Therefore, it's not outside of human ability to be able to push the molecules of many of these substances closer together.

Covalent substances also tend to be insoluble in water. (Whoops, forgot to talk about solubility in regards to metals. Ah well, I guess you've probably worked out by now that coins and other metallic objects don't tend to dissolve when dropped in water.) Also, since there aren't any charged particles in covalently-bonded molecules, covalent substances also tend to be non-conductors.

There are some covalently-bonded substances that are covalent network substances. These substances exist in a network of covalently-bonded atoms that can stretch on for quite a while. Examples include carbon in the forms of diamond and graphite. I think silicon dioxide is also a covalent network substance.

Since there are no intermolecular forces to worry about here, covalent network substances are wholly bound together by covalent bonds. Therefore, covalent network substances are extremely hard, with high melting and boiling points, due to the strength of the covalent bonds. Just like covalent molecular substances, covalent network substances are also insoluble in water and don't conduct electricity. At least one exception exists to the non-conductor rule, however, and that is graphite.

Graphite exists in layers of carbon atoms. In each layer, each carbon atom is bonded to 3 other atoms, even though the maximum number of bonds that carbon can make is 4. This leaves one delocalised electron. The delocalised electrons move between the layers of carbon atoms. As the electrons are delocalised and therefore freely-moving between the layers of carbon atoms, carbon can conduct electricity.

So there you have it- explanations on the three major types of chemical bonding. If you have any questions, please ask!