Orbital theory and crystal field theory models, 1981.
© Science Museum / Science & Society Picture Library
These theories are illustrated by a set of models made by Crystal Structures Ltd. Atomic orbitals are the region surrounding the nucleus of an atom or molecule where an electron is most likely to be found. Quantum theory dictates that the position of an electron cannot be known for certain. Some positions are more likely than others, however, and these more probable positions make up the orbital. An atom or molecule has numerous orbitals, each with a fixed size and shape. They fall into four types, defined by their shapes, and are known as 's', 'p', 'd' and 'f' orbitals. Crystal field theory describes the behaviour of elements which have only partially filled 'd' or 'f' orbitals.