Chemical Formulas
 Tell
type & number atoms in compound
 Microscopic level:


imagine 1 atom, molecule, or formula unit
Formula gives atom ratios
 Macroscopic


level:
imagine working in lab
Formula gives mole ratios
Formulas
Ex: 2H2O can mean


2 molecules of water
2 moles of water
2H2O molecules contain:
4 H atoms & 2 O atoms
2 Moles of H2O molecules contain:
4 moles of H atoms & 2 moles of O atoms
What can say about CuSO45H2O?

It’s hydrated salt

1 mole CuSO4 contains 5 moles water

When heated water is driven off & anhydrous salt
is left: CuSO4

mole ratio in formula can be used to predict how
much water found in any size sample

If had 2 moles of CuSO45H2O, how much water
would you lose on heating?
Ionic vs. Covalent Formulas
 By
looking at the type of atoms, we
can decide if the substance is an ionic
compound or a molecular (covalent)
compound.
Molecular (covalent) compounds have all
nonmetals.
Ionic compounds usually have metal +
nonmetal.
Empirical Formulas
Empirical Formula
 Smallest
whole # ratio of elements in
compound
 Ionic
compounds have only empirical
formulas
 Covalent
compounds have empirical and
molecular formulas
Molecular Formulas
Molecular Formulas
 Gives
exact composition of molecule
 Molecular
compounds have both empirical
and molecular formulas

can be same or different
Relationship between empirical and
molecular formulas
 molecular
formula is whole number
multiple of empirical formula
 Molecular
Formula =
n (Empirical Formula)
n


is small whole number
multiplies subscripts
sometimes, n = 1
Molecular Formula
 If
know empirical formula and molar mass, can
find molecular formula



Step 1: Find mass of empirical formula
Step 2:__Molar mass__ = whole number (n)
Empirical mass
Step 3: Multiply subscripts in
empirical formula by n
Finding Molecular Formulas

Find molecular formula for substance whose
empirical formula is CH and whose molar mass =
78.0 g



Step 1: Empirical mass = 13.0 g
Step 2: Molar mass = n
Empirical mass
78g = 6
13g
Step 3: 6 x subscripts in CH = C6H6
Say everything you can about:
NaCl
Ionic, empirical
CH4
C 6H 6
Covalent, molecular
Covalent, empir., molec?
C8H18
Covalent, molecular
CaBr2
Ionic, empirical
CF4
Covalent, empirical,
molecular?
KI
Ionic, empirical
CuSO45H2O
Ionic, empirical
C6H12O6
Covalent, molecular
BeSO4
Ionic, empirical
C2H4Cl2
Covalent, molecular