Why is water bent (104.5°) instead of linear, even though oxygen has only two bonds?

Oxygen has 4 electron domains (2 bonding + 2 lone pairs). The tetrahedral arrangement of domains gives a bent molecular shape. Lone pairs compress the angle below 109.5°.

Predict the molecular geometry of BF₃ and explain why it is different from NH₃.

BF₃ has 3 bonding pairs, 0 lone pairs → trigonal planar (120°). NH₃ has 3 bonding + 1 lone pair → trigonal pyramidal (107°). The lone pair on N pushes bonds closer together.

SF₆ has 6 bonding pairs around sulfur. What is its geometry and bond angle?

Octahedral geometry with 90° bond angles. Sulfur is a period-3 element that can expand its octet using d-orbitals.

Pro 🔒~25 min

Build a Molecule

3D molecular construction with real bond angles

How it works

Build a Molecule demonstrates a key principle: VSEPR (Valence Shell Electron Pair Repulsion) theory predicts molecular geometry by minimizing electron-pair repulsion around each central atom. VSEPR (Valence Shell Electron Pair Repulsion) theory predicts molecular geometry by minimizing electron-pair repulsion around each central atom. Count all electron domains (bonding pairs + lone pairs). Two domains → linear (180°). Three domains → trigonal planar (120°). Four domains → tetrahedral (109.5°). Five → trigonal bipyramidal. Six → octahedral. Lone pairs compress bond angles slightly because they occupy more space than bonding pairs. For example, water has 4 electron domains (2 bonding + 2 lone pairs) giving a tetrahedral electron geometry but a bent molecular shape with a 104.5° angle instead of 109.5°.

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Step-by-step

Select a molecule from the list.
The 3D model builds automatically — drag to rotate, scroll to zoom.
Bond angles are shown as arc labels.
Toggle the angle display on/off.
The info panel shows electron geometry, molecular geometry, and polarity.
Compare how lone pairs change the shape: methane (no lone pairs, perfect tetrahedral) vs. water (2 lone pairs, bent).

Key formulas

$\text{VSEPR: electron domains} \rightarrow \text{molecular geometry}$ Electron pairs (bonding + lone) around a central atom determine its 3D shape
$\text{Tetrahedral} = 109.5°, \; \text{Trigonal planar} = 120°, \; \text{Linear} = 180°$ Ideal bond angles for common electron domain geometries

Frequently asked questions

Why is water bent (104.5°) instead of linear, even though oxygen has only two bonds?: Oxygen has 4 electron domains (2 bonding + 2 lone pairs). The tetrahedral arrangement of domains gives a bent molecular shape. Lone pairs compress the angle below 109.5°.
Predict the molecular geometry of BF₃ and explain why it is different from NH₃.: BF₃ has 3 bonding pairs, 0 lone pairs → trigonal planar (120°). NH₃ has 3 bonding + 1 lone pair → trigonal pyramidal (107°). The lone pair on N pushes bonds closer together.
SF₆ has 6 bonding pairs around sulfur. What is its geometry and bond angle?: Octahedral geometry with 90° bond angles. Sulfur is a period-3 element that can expand its octet using d-orbitals.