Plaster of Paris, chemically known as calcium sulfate hemihydrate (CaSO4·½H2O), contains:

- 1 calcium (Ca) atom

- 1 sulfur (S) atom

- 4 oxygen (O) atoms

- 2 hydrogen (H) atoms

Thus, there are a total of 1 + 1 + 4 + 2 = 8 atoms in one formula unit of plaster of Paris.