Naming Molecular
Compounds
CO2 Carbon dioxide
CH4 methane
BCl3
boron trichloride
All are
formed from
two or more
nonmetals.
Ionic
compounds
generally
involve a metal
and nonmetal
(NaCl)
1. What are the structural differences
between ionic and molecular compounds?
2. How do those differences affect
their chemical formulas?
The chemical formula for a covalent compound
is called a molecular formula;
Example: H2O is the molecular formula of water
The chemical formula for an ionic compound
is called a formula unit.
Example: NaCl is the formula unit of
common table salt
What’s the dif?
A
VISUAL look
at the difference
will help out:
Like any ionic compound,
sodium chloride exists as a crystal:
Let’s shrink
the ions so
we can take
a peek inside
The formula unit for sodium chloride is NaCl.
However, if we look inside the crystal,
the Na+ and Cl- ions are each bonded
to six oppositely charged neighbors:
Because each Na+ is bonded to more than one Cl- ion,
and each Cl- is bonded to more than one Na+ ion, then
all the ions in the whole crystal are
part of one single bonded unit,
and the crystal below would be Na32Cl32.
This is impractical, given the enormous numbers
of ions in a crystal large enough to see with our eyes.
So, only the ratio of ions is given (its empirical formula),
which is called a formula
unit.
NaCl is the formula unit for
the sodium chloride crystal.
NaCl is the smallest whole number
ratio of sodium and chloride ions
in the crystal.
What about molecules?
A
single
water
molecule
water is covalently bonded hydrogen and oxygen.
‘space filling’ model
‘ball and stick’ model
The
molecule
remains
as aunit
single
unit
The H2O
H2O molecule
remains
as a single
of three
covalently
bonded atoms.
of covalently
bonded molecules
This difference in structure between molecules and
ionic compounds is reflected in their symbols:
The molecule is represented by a molecular formula,
showing all the atoms present in the unit.
The ionic compound is represented
by the ratio of its ions, which is called a formula unit.
versus
H2O
NaCl
Molecular (Covalent) Nomenclature
for two nonmetals
 Prefix
System (binary compounds)
1. Less electronegative atom
comes first.
2. Add prefixes to indicate # of atoms. Omit
mono- prefix on the FIRST element.
Mono- is OPTIONAL on the SECOND
element.
3. Change the ending of the
second element to -ide.
Molecular Nomenclature Prefixes
PREFIX
monoditritetrapentahexaheptaoctanonadeca-
NUMBER
1
2
3
4
5
6
7
8
9
10
Molecular Nomenclature:
Examples
 CCl4

carbon tetrachloride
 N 2O

dinitrogen monoxide
 SF6

sulfur hexafluoride
More Molecular Examples
 arsenic

trichloride
AsCl3
 dinitrogen

pentoxide
N2O5
 tetraphosphorus

P4O10
decoxide
Learning Check
1.
P2O5
a) phosphorus oxide
b) phosphorus pentoxide
c) diphosphorus pentoxide
2.
Cl2O7
a) dichlorine heptoxide
b) dichlorine oxide
c) chlorine heptoxide
3.
Cl2
a) chlorine
b) dichlorine
c) dichloride
Mixed Practice
1.
2.
3.
4.
5.
6.
7.
8.
9.
Dinitrogen monoxide
Potassium sulfide
Copper (II) nitrate
Dichlorine heptoxide
Chromium (III) sulfate
Iron (III) sulfite
Calcium oxide
Barium carbonate
Iodine monochloride