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Chem Chemistry

ChemistryNEB 2074 (old course) (grade increment)

H2O gets angular structure whereas CO2 gets linear. Why ?

2

Answer

· Based on the official syllabus and past papers
Updated

The angular shape of and the linear shape of arise due to differences in their molecular geometry, which is determined by the VSEPR (Valence Shell Electron Pair Repulsion) theory and the number of lone pairs on the central atom.

Water () – Bent/Angular Shape

  • Central atom: Oxygen (O)
  • Electron pairs around O: 4 (2 bonding pairs with H, 2 lone pairs)
  • Bond angle: ~104.5° (slightly less than the ideal 109.5° due to lone pair repulsion)
  • Shape: Bent/angular because lone pairs repel bonding pairs more strongly, compressing the H–O–H angle.
H₂O (bent)H₂O (bent)
Lone pair electrons in H₂O (red = bonding pairs, blue = lone pairs)

Carbon Dioxide () – Linear Shape

  • Central atom: Carbon (C)
  • Electron pairs around C: 2 (both bonding pairs with O, no lone pairs)
  • Bond angle: 180° (ideal linear geometry)
  • Shape: Linear because there are no lone pairs to distort the bond angle.
CO₂ (linear)CO₂ (linear)
Electronegativity difference in CO₂ (C=O bonds are polar but cancel out symmetrically)

Key Reason

  • Lone pair repulsion: In , lone pairs push bonding pairs closer, reducing the bond angle.
  • No lone pairs in : Bonding pairs arrange symmetrically at 180°.
H₂O (bent)H₂O (bent)CO₂ (linear)CO₂ (linear)
Molecular shapes of H₂O and CO₂

Discussion

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