Molecular shapes explorer
Turn 3D models of molecules and ions to see how bond pairs and lone pairs set their shapes, bond angles and polarity.
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Learning objectives
- explain the shapes of, and bond angles in, molecules such as BF3 (trigonal planar); CO2 (linear); CH4 (tetrahedral); NH3 (trigonal pyramidal); H2O (bent); SF6 (octahedral) by using the Valence Shell Electron Pair Repulsion theory
- predict the shapes of, and bond angles in, molecules analogous to those specified in (d)
- explain and deduce bond polarity using the concept of electronegativity [quantitative treatment of electronegativity is not required]
- deduce the polarity of a molecule using bond polarity and its molecular shape (analogous to those specified in (d))
- Molecular Shapes and Bond Angles (VSEPR)
- Bond Energy, Bond Length and Bond Polarity
NH₃, ammonia: 3 bond pairs, 1 lone pair around N. The electron-pair geometry is tetrahedral; the shape is trigonal pyramidal with a bond angle of 107°. The bond dipoles do not cancel: the molecule is polar.
- Around the central atom
- 3 bond pairs, 1 lone pair
- Electron-pair geometry
- tetrahedral
- Shape
- trigonal pyramidal
- Bond angle
- 107°
- Molecule
- polar
Try this
0 of 4 doneTurn NH₃ so that its lone pair points straight at you. (not done yet)
The lone pair takes the fourth corner of a tetrahedron, so the three N–H bonds point away from it like the legs of a tripod.
Compare CH₄, NH₃ and H₂O. (not done yet)
Each has four electron pairs. Lone pairs repel more strongly than bond pairs, so every lone pair squeezes the bonds closer: 109.5°, 107°, 104.5°.
Turn BF₃ to look at it edge on. (not done yet)
Edge on, BF₃ is a straight line: all four atoms lie in one plane, with the three bond pairs 120° apart.
Find a molecule with polar bonds and no net dipole, and one with a net dipole. (not done yet)
Polar bonds make a polar molecule only when the shape does not let their dipoles cancel.