Writing Names and Formulas

for Binary Ionic Compounds

Chemical FormulasChemical Formulas tell us what and

how many elements are in a compound

NaCl

1 Na atom

1 Cl atom

SubscriptsSubscripts, written after the

element, identify the number of

atoms there are of each element.

H2O

2 H atoms

1 O atom

ParenthesisMultiply each atom in parenthesis by

the subscript outside of the parenthesis

(NH4)3PO4

3 Nitrogen atoms

12 Hydrogen atoms

1 Phosphorus atom

4 Oxygen atoms

Familiar Compounds

Sand

SiO2

Cane Sugar

C12H22O11

Lime

CaO

3 atoms 45 atoms 2 atoms

Writing Formulas

Binary ionic compounds have only two

types of ions

Even though the ions carry a

charge, the compounds are neutral

The number of negative ions must

equal the number of positive ions

Formula Writing Rules

1. Write the symbol and positive

oxidation numbered element

first

Magnesium Nitride

Mg +2

Representative Elements

Formula Writing Rules

2. Write the symbol of the element

that has the negative oxidation

number or charge

Magnesium Nitride

Mg + 2 N -3

Representative Elements

Formula Writing Rules

3. Write oxidation numbers of each

element, minus the charge, as the

subscript for the other element.

(Criss Cross)

Magnesium Nitride

Mg + 2 N -3

Mg3N2

Representative Elements

Writing Names

1. Write the full name of the positive ion

NaCl

Sodium

2. Write the root name of the negative ion

NaCl

Sodium Chlor

Representative Elements

Writing Names

3. Add the ending ide to the root

NaCl

Sodium Chloride

Practice

BaF2 KBr Al2O3

Representative Elements

Barium Fluoride

Potassium Bromide

Aluminum Oxide

Transition Metals

Recall that transition metals can have

more than one charge.

Transition Metals

Use roman numerals to denote the

charge

Fe+2 or Fe+3

Iron (ll) Chloride Iron (lll) Chloride

FeCl2 FeCl3

Transition Metals

Writing Names

1. Write the full name of the transition

metals

PbO2

Lead

Transition Metals

Writing Names

2. Figure out the charges of the anions

PbO2 2 x O-2 = - 4

Write the equivalent number of the

anion charges as a roman numeral

after the transition metal’s name

3.

Lead (IV)

Transition Metals

Writing Names

PbO2

Add the ending ‘ide’ to the anion 3.

Lead (IV) Oxide

Practice

CuBr CuBr2

Copper (I) Bromide Copper (II) Bromide

Transition Metals

Writing Formulas

1. Figure out the charge on the anion

Chromium (II) Sulfide

Sulfide S-2

2. Compare the anion’s charge to the

roman numeral on the transition metal

Cr (II) = +2 Sulfide S-2

Transition Metals

Writing Formulas

Adjust the subscripts so that

charges on the transition metal are

equal to the anion’s total charge

3.

CrS

Sulfide S-2Chromium (II) Cr+2

Transition Metals

Writing Formulas

More Practice

Sulfide S-2

Chromium (III) Sulfide

1. Figure out the charge on the anion

Transition Metals

Writing Formulas

2. Compare the anion’s charge to the

roman numeral on the transition metal

Chromium (III) +3

S - 2 Cr +3

Cr +3 S - 2

S - 2

Sulfide S-2

+6-6

Transition Metals

Writing Formulas

Adjust the subscripts so that

charges on the transition metal are

equal to the anion’s total charge

3.

Cr2S3

Chromium (III) Sulfide

2(Cr +3) 3(S - 2)