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Writing Chemical Formulas. Basic Rules. 1. Always list the metal first (cation) 2. Follow with the non-metal (anion) 3. Polyatomic ions are usually anions except NH 4 +. Mg +2. Cl -. 1. Determine the lowest common multiple (LCM) 2. Divide each Oxidation Number
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Writing Chemical Formulas Basic Rules 1. Always list the metal first (cation) 2. Follow with the non-metal (anion) 3. Polyatomic ions are usually anions except NH4+
Mg+2 Cl- 1. Determine the lowest common multiple (LCM) 2. Divide each Oxidation Number into the LCM to determine the subscripts MgCl2
Na+ O-2 Mg+2 O-2 Al+3 O-2 Pb+4 O-2 Cr+3 Br-
Na+ P-3 Ca+2 P-3 Al+3 P-3 Pb+4 P-3
polyatomic ions act as a single particle Ca+2 PO4-3 NH4+ Cl-
Nomenclature (naming ionic compounds) 1. Name the metal or cation first. 2. If a binary compound, name the nonmetal (change ending to "ide"). 3. If a polyatomic ion just say its name. 4. If the cation has multiple possible oxidation numbers, then the name of the metal must be followed by a roman numeral indicating the oxidation number.
MgCl2 magnesium chloride CaO calcium oxide Na3P sodium phosphide
NH4I ammonium iodide K3PO4 potassium phosphate Al2(SO4)3 aluminum sulfate
Multiple Oxidation States Fe+2 FeO Fe+3 Fe2O3 iron (II) oxide iron (III) oxide chromium (VI) oxide CrO3 CrO Cr2O3 chromium (II) oxide chromium (III) oxide