1. Writing Chemical Formulas

2. Positive ions are always placed first in a chemical formula.
The symbol for each different element begins with a CAPITAL letter. (If a second letter is part of the symbol it is small case
CaSO4
Positive ions are always placed first in a chemical formula.
Cl-, Rb+
RbCl

3. The sum of the valence numbers must add to zero
Al+3, O-2  Al2O3
[2 x (+3)] + [3 x (-2)] =
= 0

4. Never write the number one (1) in a chemical formula.
Na1Br1
NaBr

5. Reduce subscripts to lowest terms.
Be4F8 becomes BeF2
This produces an empirical formula or a simple formula

6. If a polyatomic ion (radical) requires a subscript, parentheses are placed around the polyatomic ion and the subscript is placed outside the parentheses.
Pb+4, SO42-
Pb(SO4)2