Chemical Formulas Review

Transition Metals and PolyatomicIons

Transition Metals

•Recall:

–Transition metals (with few exceptions)form cation with more than one possiblecharge

•Ex: Fe Fe2+, Fe3+; Pb Pb2+, Pb4+

–In ionic compounds, these charge are alsotheir oxidation numbers

–We can write balanced chemical formulasby using the cross-over method

Example

•A compound containingan Sn2+ ion and a Cl- ion:

1. Sn2+ Cl-

2. Sn2+1 Cl-2

3. SnCl2

•Practice!

Write formulas that containthe following:

Pb4+ ion and O2- ion

Cr3+ ion and I- ion

Transition Metals, cont.

•Sometimes you will see a Roman numeral inparenthesis written after the name of themetal

–This represents the charge/ oxidation number ofthe ion

–Ex: Copper(II) ion  Cu2+ ion

Naming Compounds with TransitionMetals

•Stock System

–Name the metal first

•Include the charge of theion as a Roman numeralin parenthesisimmediately after

–Name the nonmetalsecond

Ex: CuCl2  copper(II)chloride

PbBr4  lead(IV)bromide

Practice:

HgS 

Fe2O3 

CoF3 

Polyatomic ions

•Ions that contain more than one atom

•Oxyanions- contain oxygen + anothernonmetal

•Negatively charged/ negative oxidationnumbers

–Only exception is ammonium (NH4+)

-1

-2

-3

AmmoniumNH4+

acetate C2H3O2−CH3COOH−

Carbonate CO32-

PhosphatePO43-

Bicarbonate HCO3-

Chromate CrO42-

Cyanide CN-

DichromateCr2O72-

Hydroxide OH-

Peroxide O22-

Nitrate NO3-

Sulfate SO42-

Nitrite NO2-

Sulfite SO32-

Perchlorate ClO4-

PermanganateMnO4-

Know These Polyatomic Ions!

Writing Chemical Formulas withPolyatomic Ions

•Use the crossover technique

•Do NOT change the subscripts of the ions!!!

•If the compound contains more than one ofthat ion, put the ion in parenthesis, and placethe subscript outside the parenthesis

Example

A compound containing Ca2+ion and NO3- polyatomic ion

1. Ca2+NO3-

2. Ca2+ 1(NO3) -2

3. Ca(NO3)2

Practice!

Write formulas containingthe following:

Na+ ion and CO32- ion

Mg2+ ion and OH- ion

Naming Compounds ContainingPolyatomic Ions

•Name metal first (watch out for transitionmetals!)

•Name polyatomic ion second

–Only exception is with ammonium- it is alwaysnamed first

Homework: Due 11-6-2012

Write balanced chemicalformulas that contain thefollowing:

1. Cr3+ ion and NO3- ion

2. Li+ and CrO42- ion

3. Sn4+ ion and N3- ion

4. NH4+ ion and PO43- ion

5. Al3+ and CO32- ion

•Name the followingcompounds:

1.PbMnO4

2.NaNO2

3.(NH4)3PO4

4.MgSO4

5.Na2O2