Naming/Writing Chemical

Formulas

Chemical formulas

A molecule’s chemical formula tells you the ratio of atoms of each element in

the compound.

1

How many of

the element

in front of it

Oxygen

Hydrogen

2H2O

Superscript

“2”

Means that

you have 2

water

molecules

CFU!

How many of each element if present?

1. NaC2H3O2 Na= C= H= O=

2. Ca3(PO4)2 Ca= P= O=

3. 3BaCl2 Ba= Cl=

STRAIGHT WITH 8!

Oxidation Numbers tell you how many electrons an atom

can lose (-) or gain (+) when forming a compound

Table of Contents

1.Naming Ionic Compounds Type I

2.Naming Ionic Compounds Type II

3.Naming Covalent Compounds

4.Naming Polyatomic Compounds

Ionic CompoundsType I

Ionic Compounds Without Transition Metals

Ionic compounds are formed when a metal gives up its electrons to a non-metal. Basically if

the compound contains a metal, it is ionic. But there are different sets of rules for

transition metals. A transition metal is an element with an atomic number of 21 to 30, 39 to

48 or 57 to 80.

A. So for a compound with any other metal, apply these rules:

1. The metal ion's name does not change regardless of charge

2. The non-metal's name ends in ide.

For example: AlCl3 = aluminum chloride

Na2S = sodium sulfide

K2O = potassium oxide

MgH2 = magnesium hydride

Notice how the little numbers (subscripts) do not affect the way we name them.

B. In going backwards (from name to formula), we will have more fun. In such a case the

total charge of the (+) and (-) ions in the compound has to be ZERO.

Example #1 What is the correct

formula for Calcium Phosphide?

Here, we have to consider the common charges for calcium and phosphorus, which are +2 and

-3, respectively. Calcium, if you recall, typically loses two electrons to get a noble gas

electron arrangement, and phosphorus needs three more electrons.

Ca+2 and P-3

So the answer is Ca3P2.

Other examples: potassium oxide : K+1 and O-2 yields K2O

aluminum bromide: Al+3 and Br-1 yields AlBr3.

Work space

If necessary!

***Lets try one where we reduce & one where we use the Carbon family

CFUExample Formula Name

H + Cl

Li + Br

C + O

Mg + Si

Rb + P

Mg + S

Ionic CompoundsType II

Ionic Compounds with Transition Metals The only difference here is that we have to specify the charge of the transition metal ion

by using a Roman numeral, and keep in mind that a transition metal is an element with

an atomic number of 21 to 30, 39 to 48 or 57 to 80.

The reason we do this is because transition metals can assume more than one charge, we

have to specify which one is involved

Example:

Iron (II) Oxide

Iron (III) Oxide

To go backwards, we need to figure out the charge of the transition metal.

Name it by writing the metal first, its charge in roman numerals, then the non-metal

with the suffix -ide

Work space

CFUExample Formula Name

Iron (II) Sulfide

Cobalt (II) Nitride

Tin (IV) Oxide

Manganese (II)

Sulfide

Covalent CompoundsType III

Roman Numerals

These are formed from non-metals that share electrons. Because there are

many sharing possibilities between two non-metals, the formula cannot be

guessed unless we have a naming system that reveals the number of atoms

involved.

The only time we drop a prefix is if the mono is to appear at the beginning

of the name.

Prefix Number of atoms

mono 1

di 2

tri 3

tetra 4

penta 5

hexa 6

Examples

1. CO

2. CO2

3. dinitrogen pentoxide

4. phosphorus trichloride

Work space

Polyatomic Compounds

Naming Polyatomic Compounds When metals are bonded to polyatomic ions, which consist of two or more atoms with one

overall charge, the same rules apply, but you have to learn the names and charges of

common polyatomic ions.

Na2CO3 = sodium carbonate. ( This is a useful chemical in purifying others; it is sometimes

called washing soda)

KNO3 = potassium nitrate ( This is an ingredient of gunpowder and it is also found in

fertilizer.)

To go backwards:

Example: Aluminum sulfate

Work space

If necessary!

Polyatomic Ion Name

OH-1 hydroxide

SO4-2 sulfate

PO4-3 phosphate

NO3-1 nitrate

CO3-2 carbonate

HCO3-1 hydrogen carbonate or

bicarbonate

ClO3-1 chlorate

NH4+1 ammonium

CFU

Example Formula

Sodium Nitrate

Aluminum Phosphate

*Silicon Sulfate

Formula Name

NaNO3

Na2SO4

Nomenclature Summary

Use this chart to help determine the names of

chemical compounds

Does the compound contain a metal?

Is the metal a TRANSITION METAL?

Use I, II, III, IV, V to indicate the charge

of the metal

Don’t use roman numerals; Don’t use

prefixesCompound is COVALENT; Mono=1,

Di=2, Tri=3, Tetra=4, Penta=5

YES

YES

NO

NO