Chemical Formulas and
Chemical Compounds
Chapter 7
Chemical Formulas
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Octane Molecule
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C8H18
Aluminum Sulfate formula unit
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Al2(SO4)3
Monatomic Ions
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Def: ions formed from a single atom
Naming ions
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Cation – use element name
Anion – change ending of element to -ide
Monatomic Ions
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d – block elements and others with
multiple ions
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Use Roman numeral in name
Fe+3  Iron(III) ion
Fe+2  Iron(II) ion
Metals always have positive charge
Polyatomic Ions
Polyatomic Ions
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NO3-  Nitrate
NO2-  Nitrite
The –ate means 1 more oxygen
SO4-2  Sulfate
SO3-2  Sulfite
Polyatomic Ions
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ClO4-  Perchlorate
ClO3-  Chlorate
ClO2-  Chlorite
ClO -  Hypochlorite
Binary Ionic Compounds
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Def: composed of 2 elements
Total (+) charge must = total (-) charge
Write the formula:
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Mg and Cl
K and N
Al and O
Compounds with Polyatomic
Ions
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Iron(II) and Nitrite
Boron and Perchlorate
Ammonium and Oxygen
Naming Ionic Compounds
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Name the cation first, then the anion
NaOH
RbCl
Ag2SO3
Fe3N2
Al(MnO4)3
Writing Formulas
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Potassium sulfide
Copper(II) sulfate
Sodium carbonate
Calcium chloride
Naming Binary Covalent
Compounds
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CO, CO2
We use PREFIXES in the name!!
Prefixes
Mono-
One
Hexa-
Six
Di-
Two
Hepta-
Seven
Tri-
Three
Octa-
Eight
Tetra-
Four
Nona-
Nine
Penta-
Five
Deca-
Ten
Covalent Naming Rules
1. Use prefixes to show how many of each
element
•
Single atom in first element, mono is not
used
2. The second element name ends in –ide
3. Drop vowel at end of prefix if element
begins with vowel (except: di and tri)
Examples
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N2O4
PCl5
Nitrogen Dioxide
Boron Trifluoride
Diphosphorus Pentoxide
Naming Acids
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2 types of acids:
1. Oxyacids: hydrogen and
polyatomic ion
2. Binary Acids: hydrogen and
halogen
Naming Oxyacids
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Replace ending of anion name
Anion Suffix
Acid Suffix
- ite
- ous
- ate
- ic
Naming Oxyacids
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H2SO4  anion SO4-2  Sulfuric Acid
H2SO3  anion SO3-2  Sulfurous Acid
HClO4
HNO3
Naming Binary Acids
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Hydrogen and a halogen
Use prefix hydroUse suffix –ic
Followed by acid
Naming Binary Acids
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HCl
HF
HI
HBr
Formula Mass
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Mass of H2O?
Formula Mass: mass of molecule,
formula unit, or ion is sum of masses of
all atoms represented (amu)
Ca(NO3)2
Molar Mass
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Def: mass of 1 mole of compound –
use molar masses of elements (g/mol)
(NH4)2CrO4
Molar Mass in Conversions
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Remember flow chart??
What is mass (g) of 3.04 mol of
ammonia vapor, NH3?
How many molecules are in 4.15 x 10-5g
C6H12O6?
More Conversions
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How many H atoms are in 7.1 moles of
C6H12O6?
How many formula units are in 4.5 kg
Ca(OH)2?
What is the mass of H2SO4, if you have
1.53 x 1023 sulfate ions your
compound?
Percent Composition
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A basket of fruit = 120 g
3 apples = 50 g
2 oranges = 35 g
2 bananas = 20 g
Basket = 15 g
What percentage of the basket’s mass
is from the apples?
Percent Composition
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What is the percent composition by
mass of each element in (NH4)2O?
What percentage by mass of
Al2(SO4)36H2O is water?
Empirical Formula
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Def: formula showing smallest wholenumber mole ratio
Ex: B2H6  Molecular Formula
BH3  Empirical Formula
Finding Empirical Formula
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Determine the empirical formula of the
compound with 17.15% C, 1.44% H,
and 81.41% F.
CHF3
Finding Empirical Formula
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Find empirical formula of 26.56% K,
35.41% Cr, and rest O.
K2Cr2O7
Finding Molecular Formula
x(empirical formula) = molecular formula
x(Emp.Form Mass) = Molec.Form Mass
x = Molecular Mass
Empirical Mass
Finding Molecular Formula
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Determine molecular formula of
compound with empirical formula CH
and formula mass of 78.110 amu.
Finding Molecular Formula
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Sample has formula mass of 34.00 amu
has 0.44g H and 6.92g O. Find its
molecular formula.