KEY POINTS:

  • Opposites may attract, but repulsion is the key to the shape of simple molecules (in those molecules which we assume to have covalent bonding present).
  • Negative charged centres – and this includes single, double or triple covalent bonds or lone pairs of electrons – repel each other to be as far apart as possible in three-dimensional space.
  • The shape of a molecule is determined by the number of negative charge centres around the central atom.
  • Two negative charge centres is linear, three trigonal planar, four tetrahedral, five trigonal bipyramid and six octahedral. There are more shapes depending on the number of negative charge centres that are lone pairs, but these are the five main ones.
  • It is the shape of a molecule, as well as differences in electronegativity between the atoms, that determines the overall polarity of a molecule. This then dictates the intermolecular forces that exist between the molecules, and the subsequent physical properties (melting points, solubility etc.)

Bonding Models and Lewis Structures

Shapes That Simple Molecules Make

Bonding and Balloons Lab

THINK OUTSIDE THE BOX:

  • Are molecules with seven or more charge centres possible? What geometrical shapes would they have?
  • Can you find the shape of molecules reflected in the structure of substances and objects around you? How about in architecture?

Bonding & Structure

Return to the previous page.

Properties

Return to the beginning of the section.