Instant Notes: Analytical Chemistry

Section E – Spectrometric techniques

E1 ELECTROMAGNETIC

RADIATION AND ENERGY

LEVELS

The nature of light and other radiation was the subject of much investigation

since Newton’s experiments in the 17th Century. It is a form of energy and may

be considered either as a continuous wave travelling through space, or as

discrete photons of the same energy. For many spectrometric techniques, the

wave approach is more useful. Figure 1 shows a representation of an electro-

magnetic wave as an oscillating electric field of amplitude E and a magnetic

field of amplitude H at right angles to each other.

Electromagnetic
radiation

Key Notes

The electromagnetic spectrum covers a very large range of wavelengths,

frequencies and energies, and many analytical spectrometric techniques

involve electromagnetic radiation.

Energy levels in atoms are defined by quantum numbers, the atoms of

each element possessing a characteristic set of discrete levels determined

by its atomic and nuclear structure.

Every molecule has several sets of discrete energy levels, which are

associated with particular structural and behavioral properties of

molecules.

Related topics Other topics in Section E.

Electromagnetic

radiation

Atomic energy

levels

Molecular

energy levels

z

y

x

H

E

λ

Direction of

propagation

Fig. 1. Plane-polarized electromagnetic radiation traveling along the x-axis.