Chapter seven – chemical formulas Chemistry Chapter seven – chemical formulas South Lake High School Science Department Ms. SANDERS

Naming Ions Ions Cation – positive charge Anion – negative charge Monatomic ions – ions formed from a single atom Polyatomic ions – ions formed from more than one atom

Naming Ions Polyatomic Ions: Ammonium - NH₄⁺¹ Acetate - CH₃COOˉ¹ Chlorate - ClO₃ˉ¹ Cyanide - CNˉ¹ Hydroxide - OHˉ¹ Nitrate - NO₃ˉ¹ Carbonate - CO₃ˉ² Sulfate - SO₄ˉ² Phosphate - PO₄ˉ³

Naming Compounds Ionic Compounds: Practice page 227: Name cation first Anion ends in –ide For writing formulas, look at group to get the charges Practice page 227: 1b) calcium chloride 1e) copper (II) sulfate 2a) Ag₂O 2b) Ca(OH)₂ 2c) KClO₃

Naming Compounds Molecular Compounds: Practice Page 229: Look at prefix (page 228); mono- 1, di- 2, tri- 3, and so on Also ends in -ide Practice Page 229: 1a) SO₃ 1c) PBr₅ 2a) carbon tetraiodide 2c) dinitrogen trioxide

Oxidation Numbers Used to keep track of the overall electron distribution In bonded atoms or polyatomic ions Oxidation numbers are assigned to the atoms Need to learn the rules on page 232

Oxidation Numbers Rules: Pure element = 0 Binary molecular compound = charge Fluorine = -1 Oxygen = -2, sometimes +2 Hydrogen = +1, except with metals = -1 The sum of the numbers must equal 0 in a neutral atom The sum of the numbers must equal the charge of an ion Monatomic ions = charge

Oxidation Numbers Practice Page 234: 1a) HCl 1b) CF₄ 1c) PCl₃ 1d) SO₂ 1e) HNO₃ 1f) KH 1g) P₄O₁₀ 1h) HClO₃

Formula and Molar Mass Get from the periodic table Formula mass – amu Molar mass – g/mole Add mass together Examples: H₂SO₄ Ca(NO₃)₂

Formula and Molar Mass Convert grams to moles (review): Given x unknown = unknown Practice page 242: How many moles are in 6.6 g (NH₄)₂SO₄?

Empirical Formula Subscripts showing smallest whole-number mole ratio Steps: % composition is the mass (g) Convert mass to moles (use molar mass) Moles to smallest ratio (divide by smallest mole)

Empirical Formula Practice page 247 Find empirical formula: 63.52% Fe and 36.48% S

Empirical Formula Practice page 247 Find empirical formula: 26.56% K, 35.4% Cr, and 38.03% O

Percent Composition % comp =(mass element/mass compound) x 100 Practice page 244: PbCl₂ What is the percent composition?