Download Chemical Compounds

Chemical Compounds
Formulae, names, and moles
Learning objectives
 Write and interpret chemical formulae for
substances
 Distinguish between ionic and covalent
compounds
 Write names for simple compounds
 Define the “mole”
 Use mole concept to determine number of
particles
 Calculate molar mass of compounds
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
 Salt is NaCl
 Glucose is C6H12O6
Distinguish between:
Ionic and covalent (molecular)
 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
Chemical formula: the use of
subscripts
 Ionic compound doesn’t
contain molecules
 Formula tells us simplest
whole number ratio of
elements
• NaCl (Na:Cl = 1:1)
• CaCl2 (Ca:Cl = 1:2)
 Covalent compound:
 Formula tells us number of
atoms in molecule
 Not necessarily simplest
• C12H22O11 – 12 C atoms, 22
H atoms, 11 O atoms
• C6H12O6 – 6 C atoms, 12 H
atoms, 6 O atoms
Formulae and counting atoms
Covalent molecules and molecular
formula
 Molecular formula gives
number of atoms in molecule
 Benzene is C6H6
 Simplest formula is CH
 But so is acetylene C2H2
 Molecular formula
distinguishes among different
compounds with same
simplest formula
Structure and properties
Naming ionic simple compounds
 Simple ionic compounds always contain
positive metal ion (cation) and negative
nonmetal ion (anion)
 Rules for names
 Metal goes first, name unchanged
 Nonmetal second, name ending → ide
 Subscripts are not specified in name
• Sodium and chlorine → sodium chloride NaCl
• Potassium and oxygen → potassium oxide K2O
• Calcium and fluorine → calcium fluoride CaF2 (not
calcium difluoride)
Anions and polyatomic ions
Naming covalent compounds
 There are no metals in covalent compounds
 What determines order of names?
 Positions in periodic table decide order
 In same period: one on left is first (NO2, OF2)
 In same group: heavier one first (ClF3, BrCl3)
 Rules
 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
Calculations with moles and
particles
 Number of particles = moles x 6.02 x 1023
 Number of moles =
particles
23
6.02x10
Weighing molecules and moles
 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 or molecule in amu has
same numerical value as molar mass in grams
 The atomic mass of carbon is 12 amu
 The molar mass of carbon is 12 g/mol
 The same is true for molecules and compounds
 The formula mass of H2O is 18 amu (1+1+16)
 The molar mass of H2O is 18 g/mol
Calculations with molar mass
 Moles =
mass
molar mass
 How many moles are in 13.88 g of lithium if
the atomic mass of Li is 6.94 amu?
 2.00