Phosphate Ion : Tetrahedral Molecular Geometry 

In this example, PO₄^3-, the Lewis diagram shows phosphorus at the center with no lone electron pairs. The phosphorus and and one oxygen are bonded through a double bond which counts as "one electron pair". Hence the molecule has four electron pairs and is tetrahedral.

The Lewis diagram is as follows:
P = 5 e-
O = 6e- x 4 = 24e-
3- charge = 3e-
Total electrons = 32

Phosphorus is an atom that may exceed an octet of electrons. Phosphates are found in certain types of rocks, which are mined and converted to fertilizer. Plants need phosphate to grow as it is incorporated in the DNA and RNA genetic molecules. Furthermore phosphate is an important structural component of bones and teeth.