Carbon atoms have a really special property.
They can form the backbone of long, complex molecules, and this is where chemistry gets really interesting.
They can do this because they share four electrons, so they can link up with other carbon atoms to form long chains, and still have room for atoms on either side.
We say that life on Earth is ‘carbon-based life’ because the molecules that make us, like proteins, carbs, fats and DNA are all based on enormous branching carbon chains.
The best way to explain how they work is to explain how ‘hydrocarbons’ work.
They are chains of carbon atoms with a hydrogen atom on each side. When the chains are short, we call them fossil fuels. When the chains are long, we call them plastics.
In other words, these chained molecules have a huge range of uses. They power our world, and are the origin of all plastics, which might make them the most significant chemical in modern civilisation.
Some different hydrocarbons. Black is a carbon atom and white is a hydrogen atom. Photo by BBC Science
Adding just a few more links in the chain gives the chemical different attributes.
Natural gas is just one carbon atom long (C1), Gasoline is four to twelve long (C4-C12), Kerosene is C10-C16, and engine oil is C18-C34.
Each of them occur naturally in a jumbled mix called crude oil. It’s extracted from the ground and seperated and categorised, a process known as oil refinement.
Short chain hydrocarbons burn easily. The reaction releases carbon dioxide and a ton of energy, and with the invention of the combustion engine they sparked the Industrial Revolution.
Plastics are hydrocarbons that are thousands of carbon atoms long.
They almost never occur naturally. We make them synthetically by combining smaller hydrocarbons. Plastics main advantage is that it can be cheaply moulded into any shape from chairs to beach balls. It’s been a breakthrough in manufacturing and play a role in almost every advanced technology.
The two basic types of plastics are Low Densite Polyethylene (LDPE) and High Density Polyethylene (HDPE). LDPE is thin and flexible, and is used for plastic bags, cling wrap, and milk cartons. HDPE is hard and rigid, and is used for bins, pipes, and toys. The difference between them is that LDPE has many branches off its main carbon chain, which forces the molecules to spread out. HDPE has no branches, so it’s molecules are densely packed together.
But as plastics are a new type of material not seen before in nature, there are few living organisms that can digest and break them down. Plastic waste like a single bottle can linger for centuries to thousands of years until the sun disintegrates them.
Despite their totally different uses, people will sometimes use plastics as a low quality substitite for fuels because of their chemical similarity.
But carbon can also branch into huge, complex molecules which we call ‘macromolecules’.
Some of them get so complicated that we can’t synthetically create them like we can with plastic. They are only created in nature by one of the most complex structures in the universe, the DNA of a living cell.
The DNA of many species creates the macromolecules are the building blocks of it’s cells. The most important types for life are carbohydrates, fats, and proteins.
For an example of how they work, an important a type of fat called a phospholipid. Phospholipids are molecules that combine two other types of molecules, each of which is made from a carbon chain.
One end, called the head, has a molecule that is polar (just like water). This means it has a slight charge, and the charge attracts water.
The other end, the tail, has a group of molecules that are non-polar. No attraction to water.
This is simple but pretty clever, as if you drop a bunch of these phospholipids into water, they will automatically arrange themselves into a sphere, with walls like in the diagram below.
DNA manufactures these molecules, and they become the walls of its cell, protecting it from the outside world.
Phospholipids naturally form a barrier against water. Source: Socratic.org
When you combine millions of clever tricks of chemistry like this, you get life. But underlying almost all of them is the basic carbon atom.