# What does a parenthesis mean in a formula?

Sep 13, 2016

It means that the atoms in a particular structure are repeated in the molecule.

#### Explanation:

An example, $C {a}_{3} {\left(P {O}_{4}\right)}_{2}$

The atomic weights of the components:

$C {a}_{3}$ means there are three Ca; $P {O}_{4}$ means there is one P and 4 oxygen, the ${\left(\right)}_{2}$ means there two $P {O}_{4}$. So, substituting in the values:

$C {a}_{3} {\left(P {O}_{4}\right)}_{2}$
(3 x 40.078) + ((30.973762 + (4 x 15.9994)) x 2)
120.234 + ((30.973762 + 63.9976) x 2)
120.234 + (94.971362 x 2)
120.234 + 189.942724
310.177

So the answer is 310.177 g/mol

The $P {O}_{4}$ carries a charge of -3, with the P and the 4 O linked by covalent bonds. One oxygen has a double bond with the P, and the other three oxygens have one covalent bond and each carry a negative charge, giving the overall charge of -3. The two $P {O}_{4}$ have a total charge of -6, and form ionic bonds with the three $C {a}^{\text{2+}}$.