Hydrocarbons.

Step 1 of 5

Chains of carbon

Organic chemistry is the chemistry of carbon compounds. There are millions of them, more than of all the other elements together, because carbon atoms bond to each other strongly and build chains, branches and rings. The Scene shows a chain of 6 carbons (grey) with hydrogens (white), as a ball-and-stick model. Look at each carbon and count the sticks coming out of it.

Step 2 of 5

Counting hydrogens

Hydrocarbons are compounds of carbon and hydrogen only. When all the bonds between the carbons are single, the hydrocarbon is an alkane: each carbon holds as many hydrogens as it can, so it is called saturated. Carbon atoms and End group are now fixed.

Step 3 of 5

The formula

You can count the hydrogens without drawing: each carbon has four bonds; the two end carbons use one of them on a neighbour, and each inner carbon uses two. That gives the general formula of the alkanes:

$\mathrm{C_nH_{2n+2}}$⁠

End group is fixed at alkane, and Carbon atoms is free.

Step 4 of 5

Names

An alkane’s name is a prefix that counts its carbons plus the ending -ane:

Carbons	Name	Formula
1	Methane	$\mathrm{CH_4}$⁠
2	Ethane	$\mathrm{C_2H_6}$⁠
3	Propane	$\mathrm{C_3H_8}$⁠
4	Butane	$\mathrm{C_4H_{10}}$⁠
5	Pentane	$\mathrm{C_5H_{12}}$⁠
6	Hexane	$\mathrm{C_6H_{14}}$⁠

When the chain has one double bond, the hydrocarbon is an alkene, ending in -ene: ethene, propene, butene. It has two fewer hydrogens, $\mathrm{C_nH_{2n}}$⁠.

Step 5 of 5

Fuels

Cooking gas, petrol, diesel and paraffin are mostly alkanes. They react with oxygen and release a lot of energy: that is combustion. The Scene shows methane, the main part of natural gas.