Numford
Lewis structure

Lewis structure of PO₄³⁻

32 valence electrons. One P=O double bond and three P-O single bonds, with no lone pair on P, so P has 10 electrons around it (an expanded octet).

OOPOO
  • P
  • O

PO₄³⁻Phosphate ion

Tetrahedral

AB₄: 4 bond pairs, no lone pairs

  • Hybridisationsp³
  • Bond angle109.5°
  • Polarityion, charge −3

Lewis structure

32 valence electrons
i

Drawn with one P=O bond (expanded octet). The double bond is shared over all four O atoms by resonance.

POOOO−−−

Formal charges: O −1 on three atoms

Why this shape

  1. P has 5 valence electrons. It uses five in one double bond to O and three single bonds to O, so none are left over.
  2. Steric number = four sigma bonds + no lone pairs = 4, so P is sp³ hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Four electron pairs point to the corners of a tetrahedron (tetrahedral electron geometry). With no lone pairs the atoms take the same shape: tetrahedral.
  4. All the bond pairs repel each other equally, so the angle is the ideal 109.5°.
  5. PO₄³⁻ is an ion with an overall charge of −3, so it is not described as polar or non-polar.
Working

How to draw it

  1. Count the valence electrons: P 5 + 4 × O 6 + 3 for the ³⁻ charge = 32 valence electrons, 16 pairs.
  2. Put P in the middle and join it to the four outer atoms with single bonds.
  3. Give each outer atom lone pairs until it has an octet (H needs only two electrons), then put any electrons left over on the central atom.
  4. Where an atom is still short of an octet, turn a lone pair of its neighbour into a shared pair: that makes a double or triple bond.
  5. Result: one P=O double bond and three P-O single bonds, with no lone pair on P, so P has 10 electrons around it (an expanded octet).
  6. Formal charge = valence electrons − lone pair electrons − number of bonds. Here: O −1 on three atoms.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Lewis structure of PO4 3-: quick answers

How many valence electrons are in PO4 3-?

P 5 + 4 × O 6 + 3 for the ³⁻ charge = 32 valence electrons, 16 pairs.

What are the formal charges in the Lewis structure of PO4 3-?

O −1 on three atoms; every other atom is zero. Formal charge = valence electrons - lone pair electrons - number of bonds.

How many lone pairs are in the Lewis structure of PO4 3-?

11 in all, none on the central P.

Try any molecule