Numford
Hybridisation

Hybridisation of CO₃²⁻

C is sp² hybridised (hybridization by the VSEPR count): 3 sigma bonds and no lone pairs give a trigonal planar shape, bond angle 120°.

OCOO
  • C
  • O

CO₃²⁻Carbonate ion

Trigonal planar

AB₃: 3 bond pairs, no lone pairs

  • Hybridisationsp²
  • Bond angle120°
  • Polarityion, charge −2

Why this shape

  1. C has 4 valence electrons. It uses four in one double bond to O and two single bonds to O, so none are left over.
  2. Steric number = three sigma bonds + no lone pairs = 3, so C is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar.
  4. All the bond pairs repel each other equally, so the angle is the ideal 120°.
  5. CO₃²⁻ is an ion with an overall charge of −2, so it is not described as polar or non-polar.

Lewis structure

24 valence electrons, 3 resonance structures
i

NCERT draws these three resonance structures; the real ion has three equal C-O bonds.

COOO−−
COOO−−
COOO−−

Formal charges: O −1 on two atoms

Working

Why this hybridisation and shape

  1. C has 4 valence electrons. It uses four in one double bond to O and two single bonds to O, so none are left over.
  2. Steric number = three sigma bonds + no lone pairs = 3, so C is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar.
  4. All the bond pairs repel each other equally, so the angle is the ideal 120°.
  5. CO₃²⁻ is an ion with an overall charge of −2, so it is not described as polar or non-polar.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of CO3 2-: quick answers

What is the hybridisation of CO3 2-?

C has 4 valence electrons. It uses four in one double bond to O and two single bonds to O, so none are left over. Steric number = three sigma bonds + no lone pairs = 3, so C is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.

What is the shape of CO3 2- and its bond angle?

Trigonal planar, with a bond angle of 120 degrees. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar. All the bond pairs repel each other equally, so the angle is the ideal 120°.

How many lone pairs are on the central atom of CO3 2-?

None. C has 4 valence electrons. It uses four in one double bond to O and two single bonds to O, so none are left over.

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