The hybridization state of a carbon bond determines that bond's strength. Bond length is greatest in sp3 hybridization and shortest in sp hybridization. Conversely, bond strength is greatest in sp hybridization and weakest in sp3 hybridization. Bond strength is the measure of the strength of the bond between two atoms.
Molecular geometry is the shape formed by the central atom, considering only bonding electron pairs. Molecular geometry can be determined by valence shell electron pair repulsion (VSEPR) theory, a covalent bond theory that uses the repulsive forces between single electrons and pairs of electrons about the central atom to predict their relative positions around the atomic nuclei. VSEPR theory suggests that valence electron pairs surrounding an atom tend to repel each other, forcing molecules to arrange themselves in a way that minimizes repulsion. According to VSEPR theory, most organic compounds have tetrahedral, trigonal planar, or linear geometry.
Methane, CH4, forms a tetrahedral shape. Water, H2O, forms a bent shape, which is a variation of tetrahedral. Ammonia, NH3, forms another variation of tetrahedral, called trigonal pyramidal. Boron trifluoride, BF3, and formaldehyde, CH2O, form a trigonal planar shape. Carbon dioxide, CO2, forms a linear shape.
Common Molecular Geometry
| Compound | Structural Formula | Bonds and Lone Pairs | Arrangement of Lone Pairs | Molecular Shape |
|---|---|---|---|---|
| Methane (CH4) | Carbon has four bonds and zero lone pairs. | Tetrahedral | Tetrahedral | |
| Water (H2O) | Oxygen has two bonds and two lone pairs. | Tetrahedral | Bent | |
| Ammonia (NH3) | Nitrogen has three bonds and one lone pair. | Tetrahedral | Trigonal pyramidal | |
| Boron trifluoride (BF3) | Boron has three bonds and zero lone pairs. | Trigonal planar | Trigonal planar | |
| Formaldehyde (CH2O) | Carbon has three bonds and zero lone pairs. | Trigonal planar | Trigonal planar | |
| Carbon dioxide (CO2) | Carbon has two bonds and zero lone pairs. | Linear | Linear |
According to VSEPR theory, valence electron pair repulsion determines molecular geometry.