Shapes of Organic Molecules

Organic molecules generally adopt specific geometric shapes, depending on the arrangement of their atoms and the number of bonds between them.

The shape of a molecule is determined by the negative electron clouds around each atom, which repel each other.
Because of this repulsion, atoms in a molecule arrange themselves in a way that maximizes the distance between them.

### Valence Shell Electron Pair Repulsion (VSEPR) Theory

This theory suggests that the repulsion between electron pairs in an atom’s valence shell causes these pairs to be oriented as far apart as possible.
Lone pairs of electrons occupy more space than bonding pairs, causing greater repulsion.
According to this theory, the shape or geometry of an organic molecule depends on the number of electron pairs in the valence shell of the central atom.

Linear shape: These molecules have two bonding areas (e.g. BeCl2, CO2), arranged 180° from each other.
Trigonal planar shape: These molecules have three bonding areas (e.g. BF3, SO3) arranged approx. 120° from each other in a plane.
Tetrahedral shape: These molecules have four bonding areas (e.g. CH4, NH4+) arranged approximately 109.5° from each other.
Trigonal bipyramidal shape: Five bonding areas (e.g. PCl5) with 90° and 120° angles between them.
Octahedral shape: Six bonding areas (e.g. SF6) are arranged in a regular octahedron, with each bond at a 90° angle to the others.

Chemical reactivity of a molecule is influenced by its shape.
Molecular shape also affects polarity and physical properties such as boiling point, melting point, and solubility.
Enzymatic reactions also depend on the shape of molecules, particularly their ability to fit into specific sites in the enzyme molecule.
Neighboring group effects that influence reaction rates and products can also depend on molecular shape.