# Explain how #4"Ca"_3("PO"_4)_2# contains #52# total atoms?

##
Ca=?

P=?

O=?

(I'm getting 22 total and not quite understanding what I've done wrong)

Ca=?

P=?

O=?

(I'm getting 22 total and not quite understanding what I've done wrong)

##### 1 Answer

Here's how I do it.

#### Explanation:

Assume you have **one** formula unit

The subscripts represent the number of atoms or groups immediately before them.

Thus,

**three**

**two**

One **one** **four**

∴ Two **two** **eight**

Let's count the number of atoms in **one** formula unit.

If 1 formula unit contains 13 atoms, then