Some substances have a trigonal planar electron group distribution but have atoms bonded to only two of the three electron groups. The shape of such molecules is trigonal planar. They adopt the positions of an equilateral triangle - 120° apart and in a plane. Examples include BeH 2 and CO 2:Ī molecule with three electron groups orients the three groups as far apart as possible. When the two electron groups are 180° apart, the atoms attached to those electron groups are also 180° apart, so the overall molecular shape is linear. A molecule whose central atom contains only two electron groups orients those two groups as far apart from each other as possible - 180° apart. Remember that a multiple bond counts as only one electron group.Īny molecule with only two atoms is linear. When applying VSEPR to simple molecules, the first thing to do is to count the number of electron groups around the central atom.

There are two types of electron groups: any type of bond - single, double, or triple - and lone electron pairs. VSEPR makes a distinction between electron group geometry, which expresses how electron groups (bonding and nonbonding electron pairs) are arranged, and molecular geometry, which expresses how the atoms in a molecule are arranged. It says that electron pairs, being composed of negatively charged particles, repel each other to get as far away from each other as possible. The basic idea in molecular shapes is called valence shell electron pair repulsion (VSEPR).

Small molecules - molecules with a single central atom - have shapes that can be easily predicted.

There is an abundance of experimental evidence to that effect - from their physical properties to their chemical reactivity. Determine the polarity of molecules using net molecular dipoles.Determine the shape of simple molecules.

Molecular shapes geometry