# Sum of the charges must be equal to the sum of the

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Sum of the charges must be equal to the sum of the negative ions and of the positive ions A formula reflects the smallest whole number ratio of ions Procedure for writing ionic compounds o 1. Write the symbol for the metal cation and its charge, followed by the symbol for the non-metal anion and its charge. Obtain charges from the elements group # in table o 2. Adjust subscript on each cation and anion to balance overall charge o 3. Check that the sum of the charges of the cations equals the sum of the charges of the anions Naming ionic compounds o For metals that form cations with one possible charge, the name is just the metal o For metals that form cations with more than 1 possible charge, the name is metal followed by the charge in roman numerals in brackets, this Fe 2+ is Iron (II), etc. o Names for nonatomic anions consist of base name of the element followed by suffix- ide o Ionic compounds with a polyatomic ion are named the same way but with the name of the polyatomic ion o If the compound contains both a polyatomic cation and polyatomic anion, noth are named Ex. NH 4 NO 3 Most polyatomic ions are oxyanions – anions containing oxygen and another element o When oxyanions contain different numbers of oxygen atoms, they are named systematically according to # of O in the ion. If there are only two ions in the series, the one with more oxygen atoms has ending –ate and the one with fewer has ending –ite. Ex. NO 3 - Nitrate Ex. NO 2 – Nitrite If there are more than 2 ions in the series, the prefixes hypo- meaning less than and per- meaning more than are used. EX. ClO - is hypochlorite (less oxygenthan chlorite) and ClO 4 - is perchlorate (more oxygen than chlorate) Hydrated ionic compounds o Some ionic compounds called hydrates have a specific # of water molecules associated with each formula unit o The H 2 O molecules are waters of hydration – they can usually be removed by heating the compound o Hydrates are named just as other ionic compounds but they are given additional name “prefix hydrate” where the prefix indicates the # of water molecules associated with each formula unit Written as: Formula unit x prefixhydrate Common prefixes o Hemi ½ o Mono 1 o Di 2 o Tri 3 o Tetra 4 o Penta 5 o Hexa 6 o Hepta 7 12
o Octa 8 NAMING MOLECULAR COMPOUNDS o Identifying molecular compounds – 2 or more nonmetals o Binary molecular compounds o Prefix – name of 1 st element – prefix – base name of 2 nd element + ide Common base names H- Hydr B – Bor C – Carb N – Nitr O – Ox F – Fluor Si – Silic P – phosph S – sulf Cl – chlor Br – brom I – iod o When writing name of molecular compound, first element is more metal-like (toward left and bottom) o Generally, write the name of the element with the smallest group # first if the two fall in same group, write the element with greatest row number first. o Prefixes are same as above but with addition of nona - 9 and deca – 10 o If there’s only one atom of the first element in the formula, the predix mono is