KENNETH EWARD / BIOGRAFX / SCIENCE PHOTO LIBRARY KENNETH EWARD / BIOGRAFX / SCIENCE PHOTO LIBRARY
Iodine pentafluoride molecule. Molecular model of iodine pentafluoride (IF5), a toxic gas. The atoms (represented by dumb-bells) are colour-coded: iodine (orange) and fluorine (red). The blue area (lower centre) is a lone pair of electrons on the iodine atom. Lone pairs are outer electrons which are not involved in a chemical bond. This molecule has a square-based pyramid shape, and is a good example of the Valence Shell Electron Pair Repulsion (VSEPR) theory. This states that bonded atoms around a central atom adopt a configuration so as to be as lone pair, atoms surrounded by five others normally have a trigonal bipyramidal shape.
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