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Chemguide: Core Chemistry 14 - 16 Answers to Set 3 of the formulae problems aluminium chloride: AlCl3 Aluminium is in Group 3 and so its ion has a 3+ charge; chlorine is in Group 7 and so its ion has a 1- charge. To balance the charges, you need three chloride ions for each aluminium ion. lithium nitride: Li3N Lithium is in Group 1 and so its ion has a 1+ charge; nitrogen is in Group 5 and so its ion has a 3- charge. (Nitrogen has 5 outer electrons, and room to accept 3 more.) To balance the charges, you need three lithium ions for each nitride ion. If you confused nitride with nitrate, take care! sodium nitrate: NaNO3 Sodium is in Group 1 and so its ion has a 1+ charge; nitrate is an ion whose formula and charge you have to remember. Nitrate ions are NO3-. (If you confused nitrate with nitride, remember to look carefully at the endings of the words.) To balance the charges, you need one of each. If you put brackets around the nitrate group, that is wrong. copper(II) nitrate: Cu(NO3)2 The Roman numeral (II) in the name tells you that copper ion has a 2+ charge; nitrate ions are NO3-. To balance the charges, you need 2 nitrate ions for each copper(II) ion. If you forgot the brackets, it is wrong. zinc sulfide: ZnS Zinc is an ion you have to learn - it has a 2+ charge; sulfur is in Group 6 and so sulfide ion has a 2- charge. (Don't confuse this with sulfate ions.) To balance the charges, you need one of each. © Jim Clark 2019 |