Question

What is the formula for the ionic compound composed of the calcium ion and the phosphate ion?

Answer 1

`Ca_3(PO_4)_2`

Explanation:

Well, the name will be simple, as by ionic bonding rules, we first write down the name of the cation, in this case calcium, and then the name of the anion, which in this case is phosphate.

The name is thus: calcium phosphate

Now, we need to criss-cross to get the chemical formula. Calcium usually exists in its `+2` state, while a phosphate ion has a `-3` charge. So, we get:

`Ca^(2+)PO_4^(3-)`

To criss-cross, we bring down the `3-` oxidation state to calcium, while phosphate will receive the `2+` state. We then remove any signs (positive or negative). The formula is thus:

`Ca_3(PO_4)_2`