Chemguide: Support for CIE A level Chemistry

These statements cover the formation of covalent bonds using some simple orbital theory, including the cases of ethane, ethene, ethyne and benzene.

The concept of hybridisation which you will meet in this topic isn't really very difficult, but you need to take your time over it.

Before you go on, you should find and read the statements in your copy of the syllabus.

You should notice that benzene is mentioned in bold type. That means that it will only be asked about in the second year of a two year course - not at AS.

First, you should read the page which looks at bonding in methane and ethane.

This page (and the next three that you will find below) come from the organic chemistry part of Chemguide. If you have already read the whole of the covalent bonding page referred to in learning outcome 3(b), you will recognise the bit about methane.

Methane isn't specifically mentioned by the syllabus, but you must be sure that you understand that before you go on to the ethane at the bottom of the page.

Don't go on to ethene (next link below) until you are sure that you understand about the formation of methane and ethane.

Now read the page about bonding in ethene.

By the time you have finished this page, it is really important that you understand the difference between a sigma bond (formed by end-to-end overlap between atomic orbitals) and a pi bond (formed by sideways overlap). Don't go on to ethyne (below) until you are sure that you understand ethene.

Now go on to look at the formation of sp hybrid orbitals by reading the page about bonding in ethyne.

For benzene, you have two options. If I was teaching it, I would want to include the benzene case to follow logically on from ethene, even though benzene won't be examined at AS.

Alternatively, you could leave this for now, and come back to it again later when it is more directly relevant to the chemistry of benzene. The danger with that is that you could end up missing it out. This statement is repeated at the beginning of the organic section of the syllabus, but not specifically when the chemistry of benzene is introduced.

I suggest, to be on the safe side, that you read this now and re-read it later on. The page you want at this stage is bonding in benzene.

Towards the bottom of that page, you will find a link to another page about the Kekulé structure for benzene. If you are coming to the benzene structure early on in the course, it would pay you to have a brief look at the first few paragraphs on that page, just looking at what the Kekulé structure is, and the paragraph about the shape.

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