Unit 6 chemistry

Unit 6

There are several types of hydrocarbon. This unit deals with naming hydrocarbons and their structure. Alkanes and Alkenes undergo a variety of important reactions, many of which are important processes in the chemical industry.

Hydrocarbons

A hydrocarbon is a substance which contains only hydrogen and carbon. The atoms within a hydrocarbon are held together by covalent bonds.

Methane

Methane has a formula CH4.

Remember: Carbon is in Group 4 so has a valency of 4 (it forms 4 bonds). Hydrogen is in group 1 so has a valency of 1 (it forms 1 bond).

Ethane

Ethane is another hydrocarbon gas. Molecules of ethane have two carbon atoms. If we build a model of a hydrocarbon with two carbon atoms we find we need six hydrogen’s to meet the rule that each carbon must form 4 bonds and each hydrogen 1 bond.

C2H6 is an easy way of writing the formula for the molecules of ethane. It does not give information about the structure of the molecules.

Alkanes

Methane and ethane are the first two numbers of a series of hydrocarbons called the alkanes.
The alkanes are a subset of the set of hydrocarbons.
Each member of the alkane series has a name which ends in '-ane' and a prefix which indicates the number of carbon atoms in the molecule.

·         Prefix: meth, No. of Carbon Atoms in the Molecule: 1, i.e. CH4 (Methane).

·         Prefix: eth, No. of Carbon Atoms in the Molecule: 2, i.e. C2H6 (Ethane).

·         Prefix: prop, No. of  Carbon Atoms in the Molecule: 3, i.e. C3H8 (Propane).

·         Prefix: but, No. of Carbon Atoms in the Molecule: 4, i.e. C4H10 (Butane).

·         Prefix: pent, No. of Carbon Atoms in the Molecule: 5, i.e. C5H12 (Pentane).

·         Prefix: hex, No. of Carbon Atoms in the Molecule: 6, i.e. C6H14 (Hexane).

·         Prefix: hept, No. of Carbon Atoms in the Molecule: 7, i.e. C7H16 (Heptane).

·         Prefix: oct, No. of Carbon Atoms in the Molecule: 8, i.e. C8H18 (Octane).

The formula for any alkane can be worked out using the general formula for the alkanes. The general formula for the alkanes is CnH2n+2 where n is the number of carbon atoms.
All members of the alkane series are known as saturated hydrocarbons, a saturated hydrocarbon is one in which all the carbon bonds are only single covalent bonds.

Uses of Alkanes

 Many of the alkanes are good fuels both as mixtures obtained from fractional distillation of crude oil and as individual compounds.
Methane is used in the home for cooking (Natural Gas). It is also burned in power stations and the energy produced is used to make electricity.
Propane and Butane gases are easily liquefied and are used as bottled gas for barbecues.

Ethane

Hydrocarbons exist where the carbon atoms are joined by a covalent double bond c=c. The simplest one is called ethane.
CH2=CH2 --> C2H4.
In the shortened structural formula it is useful to show the…