It is forming six bonds to the various oxygens, so that adds a further 6 electrons, making 12 in all. The sulphur is in Group 6 and so has 6 outer electrons. The ion has some complicated delocalisation. Taking chemistry further: In fact, all the four sulphur-oxygen bonds are identical, and the two negative charges are spread out over all four of the oxygens. The negative charges are found on two of the oxygen atoms. That means that the shapes are all pretty obvious as long as you know the bonding. In the three ions you might need to know about, not one of them has a lone pair on the central atom. Check your syllabus to find out whether you really need to bother about all this.įortunately, there is a simplifying factor. Before you can do anything else, you need to know exactly how the ion is bonded - which bonds are double, which bonds are single, and where the charges are. The shapes of ions containing double bonds In this case, our original structure misrepresented the shape. There are 2 double bond units and 1 lone pair, which will try to get as far apart as possible - taking up a trigonal planar arrangement.īecause the lone pair isn't counted when you describe the shape, SO 2 is described as bent or V-shaped. Each double bond uses 2 bond pairs and can be thought of as a single unit. 4 pairs are needed for the bonds, leaving 1 lone pair. That gives 10 electrons in total - 5 pairs. Sulphur has 6 electrons in its outer level, and the oxygens between them contribute another 4 (1 for each bond). The argument develops differently though. Sulphur dioxide could be drawn exactly the same as carbon dioxide (again without making any assumptions about the shape): The structure we've drawn above does in fact represent the shape of the molecule. Those two double bond units will try to get as far apart as possible, and so the molecule is linear. Because there are 4 bonds, these are all bond pairs.Įach double bond uses 2 bond pairs - which are then thought of as a single unit. That means there are a total of 8 electrons around the carbon, in 4 pairs. Each oxygen contributes 2 electrons - 1 for each bond. The carbon originally had 4 electrons in its outer level (group 4). The shapes of simple molecules containing double bondsĬarbon dioxide could be drawn (without making any assumptions about the shape) as Important! If you have come straight to this page via a search engine, you should read about the shapes of more simple molecules and ions before you go on. It assumes that you have just read the page on shapes of molecules and ions containing only single bonds. This page explains how to work out the shapes of molecules and ions containing double bonds. SHAPES OF MOLECULES AND IONS CONTAINING DOUBLE BONDS Shapes of molecules and ions containing double bonds
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