Writing Formulas

1. Write the symbol of the element or the polyatomic ion that has the positive oxidation number (hydrogen, ammonium ion, and all metals).

2. Write the symbol of the element of polyatomic ion with the negative oxidation number (nonmetals and polyatomic ions other than ammonium).

3. Add subscripts so that the sum of the oxidation numbers of all atoms in the formula is zero. Use the crisscross method: the charge (without the sign) of one ion becomes the subscript of the other ion.

Naming Compounds1. Write the name of the first element.

*Note: Subscripts do not become part of the name of ionic compounds but are used to determine prefixes when naming covalent compounds.

2. Write the root of the name of the second element. Ex: chlorine root is chlor- Oxygen root is ox- bromine root is brom-

3. Add the ending -ide to the root. Ex: (ionic) BaF2 – Barium Fluoride, AlCl3 – Aluminum Chloride

(Covalent) N2O – dinitrogen monoxide, CO – carbon monoxide

Practice Problems: Writing Formulas

1. Na+, Cl- _______________________

2. Zn+2, S-2 _______________________

3. Zn+2, OH- _______________________

4. Al+3, Cl- _______________________

5. K+, PO4-3 _______________________

6. Pb+4, O-2 _______________________

7. Mn+4, Br- _______________________

8. H+, Cl- _______________________

Practice Problems: Naming Compounds

1. SCl6 ______________________________

2. SiO2 ______________________________

3. CaCO3 ______________________________

4. SO2 ______________________________

5. PBr3 ______________________________

6. Mg(NO2)2 ______________________________

7. P2O5 ______________________________

8. CaCl4 ______________________________

Polyatomic IonsCharg

eName Formula

1+ Ammonium NH4+

1- Acetate C2H3O2-

1- Chlorate ClO3-

1- Hydroxide OH-

1- Nitrate NO3-

2- Carbonate CO32-

2- Sulfate SO42-

3- Phosphate PO43-

Prefixes for Binary Covalent Compounds# of

Atoms1 2 3 4 5 6 7 8

Prefix mono di tri tetra penta hexa hepta octa

Li1+, N3- Pb2+, O2-

Ni3+, O2-

Atomic Mass

The Periodic Table of Elements1

12

2

33

4

4

5 6 7 8

5

6

7

10 11 12

13 14 15 16 17

18

9