Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 113

In HCN, the central carbon atom is bonded to one hydrogen atom and one nitrogen atom. Carbon requires four more electrons to complete its octet. Hydrogen requires one more electron to complete its outer shell, so carbon shares one of its electrons with it to form a single C—H bond. Nitrogen has five valence electrons and so needs a further three electrons to complete its octet. It obtains these by sharing three of its electrons with the carbon atom to form a triple bond (having six electrons). From the dot‐and‐cross diagram, there are two areas of electron density at the carbon atom (remember, a triple bond counts as one area), so to achieve minimum repulsion, the two areas need to be 180° apart from each other. The shape is therefore linear.