Parentheses indicate multiple identical groups of atoms; a subscript outside parentheses multiplies everything inside the parentheses.

Example: Pb(NO₂)₄

This could be drawn as follows:

The (NO₂) group is just this:  . Four of those groups are shown because of the subscript 4 in (NO₂)₄. Notice that there is only one Pb atom – it is not multipled by the 4 since it is not inside the parentheses.

If it was instead 3Pb(NO₂)₄ it would look the same, except you’d draw it three times:

You can count the circles to find out how many atoms of each type are present in 3Pb(NO₂)₄. When you don’t have pictures, you multiply coefficients and subscripts together to get the atom counts.

Atom Count for 3Pb(NO₂)₄

Pb atoms:
3 molecules
x 1 Pb atom per molecule
= 3 Pb atoms
_{*(Pb is not multipled by 4, because it is not inside the parentheses)}

N atoms:
3 molecules
x 1 N atom per group
x 4 groups of (NO₂)
= 12 N atoms

“O” atoms:
3 molecules
x 2 “O” atoms per group
x 4 groups of (NO₂)
= 24 “O” atoms

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