Topic: Chemical FormulasDo Now: from last years regents

Chemical Formulas

Tell type & number atoms in compound Microscopic level: Formula gives atom ratios Macroscopic level: Formula gives mole ratios

EXAMPLE

2H2O can mean

2 molecules of water

4 H atoms & 2 O atoms

2 moles of water4 moles of H atoms & 2 moles of O

atoms

NOTE: WATER IS A BINARY COMPOUND – contains 2 elements only

What happens when a chemical formula contains

CuSO45H2O

· Means contains

In this case it contains water so it’s called a hydrate

Types of formulas

Empirical Formula

Smallest whole # ratio of elements in compound

CH4 C2H6

C5H10

Molecular Formulas

Gives exact composition of molecule

CH4 C2H6

C5H10

Relationship between empirical and molecular formulas

molecular formula is whole number multiple of empirical formula

Molecular Formula = n (Empirical Formula)

C4H8 = 4(CH2)

Ionic Compounds

Metal and Nonmetal Their formulas are always empirical

NaCl Fe2O3

Covalent Molecules

Nonmetal only Formulas can be empirical or molecular –

need to know mass to determine

CH4 C2H6

C5H10

Say everything you can about:

NaCl C6H6 C6H12O6

CH4 CF4 BeSO4

C8H18 KI C2H4Cl2

CaBr2 CuSO45H2O

empirical

Covalent, empir., molec?

Covalent, molecular

Ionic, empirical

Covalent, molecular

Covalent, empirical, molecular?

Ionic, empirical

Ionic, empirical

Covalent, molecular

Ionic, empirical

Covalent, molecular

Lets practice- page 20

Molecular Formula If know empirical formula and molar mass, can find

molecular formula Example: Find molecular formula for substance

whose empirical formula is CH2 and whose molar mass = 84.0 g

Step 1: Find mass of empirical formula

Step 2:Molar mass = whole # (n) Empirical mass

Step 3: Multiply subscripts in empirical formula by n

• Step 1: C = 1 x 12 = 12 H = 2 x 1 = _2

14 g• Step 2: 78g = 6 14g • Step 3: 6 CH2 = C6H12