Transcript Writing Chemical Formulas - Derry Area School District

Writing Chemical
Formulas
 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
The sum of the valence
numbers must add to zero
O-2  Al2O3
 [2 x (+3)] + [3 x (-2)] =

+6
+ -6
=0
 Al+3,
 Never
write the number one (1) in a
chemical formula.
Na1Br1
NaBr
Reduce subscripts to lowest terms.
Be4F8 becomes BeF2
 This
produces an empirical formula or a
simple formula
 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, SO42Pb(SO4)2