From Linear to Tetrahedral: Common Molecule Shapes You Should Know

Molecular Geometry Explained: Shapes, Angles, and Examples

Molecular geometry describes the three-dimensional arrangement of atoms in a molecule. Geometry determines many properties—polarity, reactivity, intermolecular forces, color, and biological activity. This article explains common molecular shapes, how bond angles arise, the VSEPR method for prediction, and clear examples.

Why shape matters

• Polarity: Asymmetric shapes produce net dipoles.
• Reactivity and mechanism: Steric hindrance and orbital alignment depend on geometry.
• Physical properties: Boiling/melting points and solubility relate to molecular shape and resulting intermolecular forces.

How shapes form: basic principles

• Electron domains (bonding pairs and lone pairs) around a central atom repel each other and arrange to minimize repulsion.
• Bonded atoms adopt positions that reduce electron-pair repulsion; lone pairs take more space than bonding pairs, compressing bond angles.
• Hybridization of the central atom (sp, sp2, sp3, sp3d, sp3d2) helps explain observed geometries and bond angles.

VSEPR basics (Valence Shell Electron Pair Repulsion)

1. Count electron domains around the central atom: each single, double, or triple bond counts as one domain; each lone pair counts as one domain.
2. Arrange domains to minimize repulsion (linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral).
3. Adjust ideal angles for lone-pair repulsion and multiple bonds.

Common molecular shapes, ideal angles, and examples

• Linear — 180°

  • Electron domains: 2
  • Example: CO2 (O=C=O)

• Trigonal planar — 120°

  • Electron domains: 3
  • Example: BF3

• Bent (angular) — ~120° (for 3 domains with one lone pair); ~104.5° (for 4 domains with two lone pairs)

  • Electron domains: 3 or 4 with lone pairs
  • Examples: SO2 (one lone pair), H2O (two lone pairs, ~104.5°)

• Tetrahedral — 109.5°

  • Electron domains: 4
  • Example: CH4

• Trigonal pyramidal — ~107°

  • Electron domains: 4 (one lone pair)
  • Example: NH3

• Trigonal bipyramidal — 90° and 120°

  • Electron domains: 5
  • Example: PCl5

• Seesaw — <90° and <120°

  • Electron domains: 5 (one lone pair)
  • Example: SF4

• T-shaped — ~90°

  • Electron domains: 5 (two lone pairs)
  • Example: ClF3

• Octahedral — 90°

  • Electron domains: 6
  • Example: SF6

• Square pyramidal — <90°

  • Electron domains: 6 (one lone pair)
  • Example: BrF5

• Square planar — 90°

  • Electron domains: 6 (two lone pairs opposite)
  • Example: XeF4

Bond angles and deviations

• Lone pairs occupy more space than bonding pairs because lone-pair electrons are localized closer to the nucleus; this compresses adjacent bond angles (e.g., NH3 < CH4 < H2O).
• Multiple bonds exert greater repulsion than single bonds, slightly reducing adjacent bond angles.
• Differences in electronegativity can subtly change bond angles by shifting electron density.

Predicting molecular polarity

• Determine molecular geometry and vector sum of bond dipoles.
• Symmetrical geometries (linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral) can be nonpolar if all outer atoms are the same. Asymmetry or lone pairs typically yield a net dipole.

Quick worked examples

1. CO2

   • Central atom: C; electron domains: 2 → linear (180°). Bond dipoles cancel → nonpolar.

2. H2O

   • Central atom: O; electron domains: 4 (two lone pairs) → tetrahedral electron geometry, bent molecular shape (~104.5°). Polar due to net dipole.

3. SF4

   • Central atom: S; electron domains: 5 (one lone pair) → trigonal bipyramidal electron geometry, seesaw molecular shape. Polar.

4. XeF4

   • Central atom: Xe; electron domains: 6 (two lone pairs opposite) → octahedral electron geometry, square planar molecular shape. Nonpolar if outer atoms identical