Chemical Equations
Formulae, names, equations,
moles and stoichiometry
Learning objectives
 Write chemical formulae for substances
 Write names for simple compounds
 Apply conservation of matter to balance simple
chemical equations
 Define the “mole”
 Calculate molar mass of compounds
 Apply the mole concept to chemical reactions
 Describe concentration using molarity, percent and
ppm
Most substances are compounds
 Two or more elements combined
 Constant Composition:
 Compound always contains same amount of
each element
 Chemical formula tells us the number of
atoms of each element
 Water is H2O
Chemical formula: the use of
subscripts
 Ionic compound:
 Formula tells us ratio of the elements
• NaCl (Na:Cl = 1:1)
• CaCl2 (Ca:Cl = 1:2)
 Covalent compound:
 Formula tells us number of atoms in molecule
• C12H22O11 – 12 C atoms, 22 H atoms, 11 O atoms
Formulae and counting atoms
Ionic and covalent
 Ionic (sodium chloride) contain ions
 Charged particles
 Electron transfer
 Solutions conduct electricity (electrolytes)
 Covalent (sugar) contain molecules
 No charged particles
 Atoms share electrons
 Solutions don’t conduct electricity
Covalent molecules and molecular
formula
 Molecular formula gives number of atoms in
molecule
 Benzene is C6H6
 Simplest formula would be CH
 But so is acetylene C2H2
 Molecules can contain thousands of atoms –
each one plays a role
Naming ionic simple compounds
 Simple ionic compounds contain positive
metal ion (cation) and negative nonmetal ion
(anion)
 Metal goes first, name unchanged
 Nonmetal second, name ending → ide
 Subscripts are not named
• Sodium and chlorine → sodium chloride NaCl
• Potassium and oxygen → potassium oxide K2O
• Calcium and fluorine → calcium fluoride CaF2
Anions and polyatomic ions
Naming covalent compounds
 There are no metals:
what’s the order?
 More “metallic” one first
 Less “metallic” one second,
end → ide
 Subscripts are stated
(except if first one is one)
• CO2 Carbon dioxide
• N2O Dinitrogen monoxide
• P2O5 Diphosphorous
pentoxide
Counting particles: The Mole
 The mole is a unit of quantity used in
chemistry to measure the number of atoms
or molecules
 DEFINITION:
 The number of atoms in exactly 12 g of 12C
 A mole of anything always has the same
number of particles: atoms, molecules or
potatoes – 6.02 x 1023 – Avogadro’s number
Atomic and molecular masses
 Two scales:
 Atomic mass unit scale
 The mass of an individual atom or molecule in
atomic mass units (amu)
 Molar mass scale
 The mass of a mole of atoms or molecules in
grams
 Confusing?
The Good News
 The mass of a single atom in amu has the same
numerical value as its molar mass in grams
 The atomic mass of carbon is 12 amu
 The molar mass of carbon is 12 g
 The same is true for molecules and compounds
 The formula mass of H2O is 18 amu
 The molar mass of H2O is 18 g
Examples
 How many moles are in 13.88 g of lithium if
the atomic mass of Li is 6.94 amu?
 2.00
 What is the molar mass of CH4 if the atomic
mass of H = 1 amu and C = 12 amu
 16 g
Some molar mass examples