1. Multiply the total number of atoms inside the parentheses by the
Totaling Atoms Using PSEC
Parentheses
Count up the total number of atoms inside the parentheses
Subscripts
Multiply the total number of atoms inside the parentheses by the
subscript value
Extras
Add any extra atoms that were not yet accounted for to the total
Coefficients
Multiply the total number of atoms (from PSE) by the coefficient

2. Examples Parentheses Subscripts Extras Coefficients 2Ba(NO3)2
4(NH4)3PO4
P – 4 atoms total
N 1
O 3
4 atoms
Parentheses
P – 5 atoms total
N 1
H 4
5 atoms
Subscripts
S – 8 atoms total
(4)(2) = 8 atoms
S – 15 atoms total
(5)(3) = 15 atoms
Extras
E – 9 atoms total
8 + 1 = 9 atoms
E – 20 atoms total
= 20 atoms
C – 18 atoms total
(9)(2) = 18 atoms
Coefficients
C – 80 atoms total
(20)(4) = 80 atoms