Numford
Hybridisation

Hybridisation of PO₄³⁻

P is sp³ hybridised (hybridization by the VSEPR count): 4 sigma bonds and no lone pairs give a tetrahedral shape, bond angle 109.5°.

OOPOO
  • P
  • O

PO₄³⁻Phosphate ion

Tetrahedral

AB₄: 4 bond pairs, no lone pairs

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

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.

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

Working

Why this hybridisation and 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.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of PO4 3-: quick answers

What is the hybridisation of PO4 3-?

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. 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.

What is the shape of PO4 3- and its bond angle?

Tetrahedral, with a bond angle of 109.5 degrees. Four electron pairs point to the corners of a tetrahedron (tetrahedral electron geometry). With no lone pairs the atoms take the same shape: tetrahedral. All the bond pairs repel each other equally, so the angle is the ideal 109.5°.

How many lone pairs are on the central atom of PO4 3-?

None. 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.

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