Chapter 4, Section 3
Compound Names
and Formulas
Naming Ionic Compounds
Model Molecule:
 Sodium Chloride
Cation name “regular”
Anion name gets -ide
ending
Covalent Bonds
Model Molecule:
Carbon Monoxide
These compounds are named
using prefixes to show number of
atoms.
Prefixes for Covalent
Compounds
1 Mono
6 Hexa
2 Di
7 Hepta
3 Tri
8
4 Tetra
5 Penta
Octa
9 Nona
10 Deca
Transition Metals
 These are the metals on the “bridge” or
short part of the periodic table, running
along the center.
 These metals can have more than one
charge. Sometimes, for example, iron (Fe)
gives up 2 electrons, and sometimes 3.
If it helps,
 Think about some
brave Roman soldiers,
fighting to the death
on a bridge - each
man wielding a metal
sword and a metal
shield.
Roman Numerals
1=I
2 = II
3 = III
4 = IV
Transition Metals, con.
 So iron can form both FeO and Fe2O3,
depending on the number of electrons the
iron atoms gave up. In order to identify
which “iron oxide” you’re talking about,
you have to use Roman numerals to
indicate the charge of the cation in the
compound.
“Iron Oxide”
 In FeO, the oxygen has a valence of 6,
and so it takes two electrons, giving it a 2charge.
 It gets the two electrons from the one iron
atom - so the iron atom must have a 2+
charge.
 This makes the name iron (II) oxide,
 where the Roman numeral II indicates
that the charge is 2+
Iron Oxide
 In Fe2O3, the 3 different oxygen atoms
would each take 2 electrons, for a total of
6 Where did they get them?
 From the 2 different iron atoms. If the
total number of electrons taken is 6, then
the total number of electrons given must
be 6.
 So gave up 3 electrons each.
FeI2
 Fe is a transition metal, so it can have
more than one possible number of
valence electrons.
 But Iodine is a halogen, so it definitely
has a valence of 7, so it will take 1
electron.
 There are two iodines in the formula, and
each of them must have taken 1 electron,
for a total charge of 2 So it must be iron (II) iodide
MnF3
 Manganese (not magnesium!) is a
transition metal. Flourine is a halogen,
(1-)
 If each of the 3 fluorines took 1 electron,
the manganese atom must have given up
3.
 So it’s
manganese (III) fluoride
Another Example
 What is the formula for aluminum fluoride?
 Aluminum has 3 valence electrons, for a charge
of 3+
 Fluorine, a halogen, has a valence of 7, so it
wants one more electron, for a charge of 1 It will take 3 fluorines to take all 3 of the
aluminum valence electrons, so the formula will
be AlF3
Cross your heart!
 CaCl2
Al2O3
Al2O3