Section 7-3

Section 7.3 Names and Formulas for Ionic Compounds

• Relate a formula unit of an ionic compound to its composition.

nonmetal: an element that is generally a gas or a dull, brittle solid and is a poor conductor of heat and electricity

• Write formulas for ionic compounds and oxyanions.

• Apply naming conventions to ionic compounds and oxyanions.

Section 7-3

Section 7.3 Names and Formulas for Ionic Compounds (cont.)

formula unit

monatomic ion

oxidation number

polyatomic ion

oxyanion

In written names and formulas for ionic compounds, the cation appears first, followed by the anion.

Section 7-3

Formulas for Ionic Compounds (cont.)

• A formula unit represents the simplest ratio of the ions involved.

• Monatomic ions are one-atom ions.

• Negative monatomic ions always end with –ide

• Example: oxygen becomes oxide as an anion

• Positive monatomic ions keep their name

• Example: sodium stays sodium as a cation

Section 7-3

Formulas for Ionic Compounds (cont.)

• Oxidation number, or oxidation state, is the charge of a monatomic ion.

Section 7-3

Formulas for Ionic Compounds (cont.)

• Polyatomic ions are ions made up of more than one atom.

• Never change subscripts of polyatomic ions, place in parentheses and write the appropriate subscript outside the parentheses.

• Write the symbol for each ion including the charge, Cation first then Anion.

• Overall charge must equal zero.– If charges cancel, just write symbols.– If not, use subscripts to balance charges.– Subscripts represent the number of ions

of each element in an ionic compound.

• Use parentheses to show more than one polyatomic ion.

Formulas for Ionic Compounds

Ionic Compound FormationExample: Aluminum sulfide

1. Write the formulas for the cation and anion, including CHARGES!

AlAl3+3+ SS2-2-2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced!

22 33

Example: Zinc hydroxide

1. Write the formulas for the cation and anion, including CHARGES!

ZnZn2+2+ OHOH--2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced!

( )( )22

Example: Magnesium carbonate

1. Write the formulas for the cation and anion, including CHARGES!

MgMg2+2+ COCO332-2-2. Check to see if

charges are balanced.

They are balanced!

Example: Iron(III) chloride

1. Write the formulas for the cation and anion, including CHARGES!

FeFe3+3+ClCl--2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced!

33

• potassium chloride

• magnesium nitrate

• copper(II) chloride

– K+ + Cl

– Mg2+ + NO3

– Cu2+ + Cl

KCl

Mg(NO3)2

CuCl2

Ionic Compound Formation

Ionic Compound Nomenclature (naming)

• Write the name of the Cation followed by the name of the Anion

• Cations keep their original name• Change ending of monatomic anions to -ide.• Polyatomic ions have special names. (learn

them) • Metals with multiple Charges (oxidation

numbers) have Roman Numerals that indicate the positive charge on the ion

Section 7-3

Names for Ions and Ionic Compounds

• An oxyanion is a polyatomic ion composed of an element (usually a non-metal), bonded to one or more oxygen atoms.

Section 7-3

Names for Ions and Ionic Compounds (cont.)

Section 7-3

Names for Ions and Ionic Compounds (cont.)

• NaBr

• K2CO3

• FeCl3

– sodium bromide

– potassium carbonate

– iron(III) chloride

Examples

A. A

B. B

C. C

D. D

Section 7-3

A B C D

0% 0%0%0%

Section 7.3 Assessment

Which subscripts would you most likely use for an ionic compound containing an alkali metal and a halogen? (Remember, 1 = no written subscript)

A. 1 and 2

B. 2 and 1

C. 2 and 3

D. 1 and 1