Chapter 4, Section 3

Compound Names

and Formulas

Naming Ionic Compounds

Model Molecule: Sodium ChlorideCation name “regular”

Anion name gets -ide ending

Covalent Bonds

Model Molecule:

Carbon MonoxideThese compounds are named

using prefixes to show number of atoms.

Prefixes for Covalent Compounds1 Mono2 Di3 Tri4 Tetra5 Penta

6 Hexa7 Hepta8 Octa9 Nona10 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 2- charge.

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. each of the two iron atoms

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