Writing Formulas

Oxidation Numbers & Chemical Formulas

Mrs. Wolfe

Vocabulary:

• Another word for Charge is OXIDATION NUMBER.

Is there a pattern of Oxidation Numbers on the Periodic Table?

• What is the charge of a Hydrogen ion?

• + 1 (sometimes –1)

• Lithium?

• Also +1

• Beryllium? Magnesium?

• Both +2

• Fluorine? Chlorine?

• Both -1

• There IS a pattern! Let’s write that on our Periodic Tables.

+1

+2 +3 NA -3 -2 -1

0

Common Oxidation Numbers

There are some Polyatomic Ions.

• Polyatomic Ions – combination of elements WITH A CHARGE!

• You will always have a chart of their oxidation numbers on a test/quiz.

• HERE COMES A HANDOUT!

We can use oxidation numbers to write formulas.

Remember, compounds must be NEUTRAL.

Cl

1Na

1 NaCl

Ionic Bonds & Formulas

• Write each ion, cation first.

• Use parentheses to show more than one polyatomic ion.

• Roman numerals = transition metal ion’s charge

• potassium + chlorine

• magnesium + nitrate

• copper(II) + chlorine

K+ Cl

Mg2+ NO3

Cu2+ Cl

KCl

Mg(NO3)2

CuCl2

Practice Problems:

Time for a WS, then Labs!

• Qualitative Ion Testing Lab• Formula of an Ionic Compound Lab

Some elements are diatomic.

N O F

Cl

Br

I

H

The SEVEN diatomic elements

Br2 I2 N2 Cl2 H2 O2 F2

Time for a WS, then GAMES!

• Formulas of Compounds WS• Rummy!

Naming Ionic Compounds

• Write the names of both ions, CATION first.

• Change ending of ANION to -ide.

• Polyatomic ions have special names.

• Use Roman numerals to show the ion’s charge if more than one is possible. (Transition metals)

• NaBr

• Na2CO3

• FeCl3

– sodium bromide

– sodium carbonate

– iron(III) chloride

Practice Problems

Naming Covalent Compounds

1. Less e-neg atom comes first.

2. Add prefixes to indicate # of atoms.

3. Change the ending of the second element to -ide.

PREFIXmono-di-

tri-tetra-penta-

hexa-

hepta-

octa-nona-

deca-

NUMBER12345678910

Molecular Prefixes

• CCl4

• N2O

• SF6

– carbon tetrachloride

– dinitrogen monoxide

– sulfur hexafluoride

Practice Problems

• arsenic trichloride

• dinitrogen pentoxide

• tetraphosphorus decoxide

– AsCl3

– N2O5

– P4O10

Practice Problems

Let’s do a WS!