Bent Molecular Geometry
Definition and meaning of Bent Molecular Geometry in chemistry.
Bent molecular geometry describes a molecule in which a central atom is bonded to two other atoms but also carries one or more lone pairs, forcing the three atoms into an angle rather than a straight line. Water and sulfur dioxide are common examples.
In more detail
A bent shape, also called angular, arises because lone pairs on the central atom take up space and push the bonding pairs closer together. VSEPR theory treats lone pairs as electron regions that repel other regions even though they are not visible as atoms. When two atoms are bonded to a central atom that also holds lone pairs, the result is a molecule that looks like a wide V. There are two common versions of the bent shape.
In the first, the central atom has four electron regions total: two bonds and two lone pairs. The electron geometry is tetrahedral, but because two of the corners are lone pairs, the visible shape is bent. Water, H2O, is the classic case, with a bond angle of about 104.5 degrees, slightly less than the ideal 109.5 because the two lone pairs squeeze the bonds together.
In the second version, the central atom has three electron regions: two bonds and one lone pair. The electron geometry is trigonal planar, but one corner is a lone pair, so the molecule is again bent, this time with an angle near 120 degrees. Sulfur dioxide, SO2, and ozone, O3, fit this pattern.
The bent shape has important consequences. Because the molecule is not symmetric, the individual bond dipoles do not cancel, so a bent molecule with polar bonds is usually polar overall. Water's bent shape is the reason it has a strong dipole and can dissolve many ionic and polar substances.
Without the lone pairs bending the molecule, water would be linear and nonpolar, and it would behave very differently.
Key facts
| Field | General Chemistry |
|---|---|
| Also called | angular |
| Version 1 | 2 bonds + 2 lone pairs (~104.5 degrees) |
| Version 2 | 2 bonds + 1 lone pair (~119 degrees) |
| Example (v1) | H2O |
| Example (v2) | SO2, O3 |
| Cause | lone pair repulsion |
| Polarity | usually polar |
Water, H2O, has two O-H bonds and two lone pairs on oxygen. The lone pairs push the bonds to an angle of about 104.5 degrees, giving water its bent shape and its strong overall polarity.
Frequently asked questions
Why is water bent instead of straight?
Oxygen has two lone pairs in addition to its two bonds. These lone pairs repel the bonding pairs and push the hydrogen atoms into an angle of about 104.5 degrees rather than a straight line.
What is the difference between the two bent shapes?
One comes from four electron regions (two bonds, two lone pairs) with angles near 104.5 degrees, like water. The other comes from three regions (two bonds, one lone pair) with angles near 120 degrees, like SO2.
Are bent molecules polar?
Usually yes. The angular shape prevents the bond dipoles from canceling, so a bent molecule with polar bonds has a net dipole and is polar overall.
How is bent different from linear?
A linear molecule has two bonds and no lone pairs on the central atom, giving a 180-degree angle. A bent molecule has lone pairs that push the bonds into a smaller angle.