Chapter 3
Molecular Composition
Molecules
When nonmetals bond with other nonmetals, they do not bond as
ions. Instead, they remain uncharged and share electrons to form
covalent bonds.
These molecular compounds (molecules) tend to behave as a
single unit, not as an aggregate like ionic compounds
Ethyl acetate (“non-acetone” nail-polish
remover) - a molecular compound
Names of Ions
Naming binary ionic compounds
Named as: Cation + Anion:
NaCl =
MgBr =
Al2O3 =
ZnS =
Transition metal compounds are named similarly, but the charge
of the metal is specified:
Fe2O3 =
FeO =
HgS =
VCl3 =
TiO2 =
Naming binary ionic compounds
Named as: Cation + Anion:
NaCl = sodium chloride
MgBr = magnesium bromide
Al2O3 = aluminum oxide
ZnS = zinc sulfide
Transition metal compounds are named similarly, but the charge
of the metal is specified:
Fe2O3 =
FeO =
HgS =
VCl3 =
TiO2 =
Naming binary ionic compounds
Named as: Cation + Anion:
NaCl = sodium chloride
MgBr = magnesium bromide
Al2O3 = aluminum oxide
ZnS = zinc sulfide
Transition metal compounds are named similarly, but the charge
of the metal is specified:
Fe2O3 = Iron (III) oxide
FeO = Iron (II) oxide
HgS = Mercury (II) sulfide
VCl3 = Vanadium (III) chloride
TiO2 = Titanium (IV) oxide
Polyatomic ions
Ions composed of more than one atom
These are covalently bonded atoms that have charges, and act in
aggregate as an ion.
Polyatomic ions
Naming Polyatomic Ions
FeSO4 =
Bi(C2H3O2) 3 =
MnCO3 =
Ti(NO3)4 =
Pt(CN)4 =
Naming Polyatomic Ions
FeSO4 = iron (II) sulfate
Bi(C2H3O2) 3 = bismuth (III) acetate
MnCO3 = manganese (II) carbonate
Ti(NO3)4 = titanium (IV) nitrate
Pt(CN)4 = platinum (IV) cyanide
Binary nonmetalic compounds
If a pair of atoms can form more than one mixture, then we use
prefixes to describe the number of each atom type:
mono 1
penta 5
di
2
hexa
tri
3
hepta 7
tetra
4
octa
6
8
Hydrated Compounds
Some ionic compounds may have water “associated” with the
compound. We describe these compounds as hydrates and name
them as such:
CoCl2
cobalt (II) chloride
CoCl2•6H2O
CuSO4
CuSO4•5H2O
copper (II) sulfate
Hydrated Compounds
Some ionic compounds may have water “associated” with the
compound. We describe these compounds as hydrates and name
them as such:
CoCl2
cobalt (II) chloride
CoCl2•6H2O
cobalt (II) chloride hexahydrate
CuSO4
copper (II) sulfate
CuSO4•5H2O
copper (II) sulfate pentahydrate
CoCl2•6H2O
CoCl2
Binary Acids
(Bronstead) Acids produce H3O+ ions when dissolved in
water
There are different rules for naming binary acids to
emphasize their acidity
HCl : not hydrogen chloride - hydrochloric acid
HI: not hydrogen iodide - hydroiodic acid
Oxoacids/oxoanions
Series of acids/anions formed by the successive addition of one
oxygen atom
XO– hypo___ite ion
HXO
hypo ___ ous acid
XO2– ___ite ion
HXO2
___ ous acid
XO3– ___ate ion
HXO3
___ ic acid
XO4– per ___ ate ion
HXO4 per ___ric acid
Oxoacids/oxoanions
Series of acids/anions formed by the successive addition of one
oxygen atom
ClO– hypochlorite ion
HClO
ClO2– chlorite ion
HClO2 chlorous acid
ClO3– chlorate ion
HClO3 chloric acid
ClO4– perchlorate ion
HClO4 perchloric acid
hypochlorous acid
Law of Conservation of Mass
Lavoisier (1743-1794): The total mass of all
substances present after a chemical reaction (the
products) is the same as the total mass of all
substances present before the reaction (the reactants)
Stoichiometry
Stoichiometry includes all the quantitative
relationships involving:
atomic and formula masses
chemical formulas
amount (moles) of substances
Mass Percent
Table salt is what percent sodium by mass?
Determining Percent Composition
From a Chemical Formula
(# of atoms of type X) (atomic mass of X)
mass % of element X =
X 100%
(formula mass of compound)
The formula mass (also called molecular mass, formula
weight or molecular weight) is the total mass of all the
elements that make up the compound
Aspartame
An unknown compound is 26.1% carbon, 4.4% hydrogen
and 69.5% oxygen by mass. What is the empirical
formula?
Finding an Empirical Formula
From Mass Percent
1.
2.
3.
4.
5.
Choose an arbitrary sample size (100g is a good choice)
Convert percent
mass
moles
Write a formula with the molar values as subscripts
Divide each subscript by the smallest subscript value
Multiply all subscripts by a small whole number to make
the subscripts integral (if necessary)