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

2. 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

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

4. 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

5. 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

6. 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

7. 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

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

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

10. 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?

11. 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)

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

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

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