Organic Chemistry

• Alkanes
• Alkenes

This is the study of one particular element - carbon. It's often called Carbon Chemistry. Carbon forms an almost infinite number of compounds. All life forms are based on a huge number of carbon compounds. Any molecule that contains only carbon and hydrogen atoms is also called a hydrocarbon

Carbon is element number 6 in the Periodic Table and has 4 electrons in its outer shell, as you can see from this diagram.

Because there are 4 electrons in the outer shell, carbon always forms compounds with 4 covalent bonds in them. These are normally drawn using 4 straight lines. Some examples of carbon compounds are given below. I have represented the atoms by their chemical symbols (C for carbon, H for hydrogen etc.), which is very common when drawing organic molecules.

This is methane, the first of a family of organic compounds called alkanes. Its formula is CH₄ and it is the gas that is used to power most household gas cookers. It is also used to fire Bunsen Burners. Methane is also known as as Town Gas or Natural Gas. Methane is a natural product formed by many biological process such as rotting rubbish. It was thought to be present on Earth before life began, and is found on Titan, the largest moon of Saturn.

This is Carbon Dioxide, CO₂. The carbon is joined to two oxygen atoms, each with a double covalent bond. If you count the number of lines coming out of the carbon atom, it still comes to 4 lines. (Double bonds count as 2).

This is the next alkane in the series, ethane, formula C₂H₆. It shows that carbon atoms can form bonds with other carbon atoms. The formula for ethane is C₂H₆. It is a gas at room temperature and pressure.

This molecule is a type of organic compound called an Organic Acid. In fact, it is ethanoic acid, (formerly called acetic acid), which is found in vinegar.

A word about notation

Organic compounds are generally represented in the way that you see above, with the symbols for each element joined by lines. The structure of the molecules is, of course, three-dimensional. The four bonds that join a carbon atom to other atoms in a compound are made up from electron sharing, and electrons, being negative, naturally repel each other so that the bonds are as far away from each other as possible.

This means that the bonds form a tetrahedral structure (similar to a pyramid, but with a triangular base). This is best shown with methane. The single carbon atom has four hydrogen atoms bonded to it, with three forming a triangular "base" and one more at the apex of the tetrahedron. Compare this 3-D diagram with the "flattened" representation of methane at the top of the page.

More complicated carbon compounds have a similar structure. Compare the realistic representation of propane (below left) with the more usual flat representation (below right)

	H | H | H | H- C - C - C -H | H | H | H
The 3-D representation of propane	How we normally represent it!

Whereas this is the correct arrangement of atoms in real life, it soon becomes impractical to show complex molecules like this, so we generally stick to the flat notation. That is what you will see in this tutorial.

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