# Compound Names and Formulas

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Compound Names and Formulas
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 Carbon Monoxide Model Molecule:
These compounds are named using prefixes to show number of atoms.

Prefixes for Covalent Compounds
1 Mono 2 Di 3 Tri 4 Tetra 5 Penta 6 Hexa 7 Hepta 8 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 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

manganese (III) fluoride
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