how many atoms!!!

[villam01]

how many nonmetal atoms do we find in Ca3 (Po4)2 ??
the answer in my book is 10. but i dont know why??

[jeffy]

Hi villam01,

There are three calcium atoms and there are two (PO₄) ions.

Each PO₄ ion contains one phosphorus atom and 4 oxygen atoms, so each ion contains five non-metal atoms.

Since there are two ions, you have 2 x 5 = 10 non-metal atoms.

[KathChem82]

i think it's Ca3(PO4)2.
The nonmetal atoms are P(phosphorus) and O (oxygen), basically we have 1 Phosphorus and 4 Oxygen but since the PO4 (phosphate) has a subscript 2, it means that we have to double everything inside the parenthesis.
So now we have
total # of nonmetal atoms = (1 Phosphorus x 2) + (4 Oxygen x 2)
= 2 Phosphorus + 8 Oxygen
= 10 nonmetal atoms