Atoms of different elements give out light of a distinctive colour when an electric discharge is passed through vapour of the element. Similarly, metals can be identified by the colour of the flame produced when their compounds are heated in a Bunsen burner.

The Electromagnetic Spectrum

Electromagnetic radiation comes in different forms of differing energy. All electromagnetic waves travel at the same speed, but they differ in their wavelength.

(e.g. blue light has shorter wavelength than red light)

The number of waves that pass a point in 1 second is called the frequency. It is related to the wavelength by the following equation.

c = vλ

S = wavelength in m

c = Speed of light 3.0 x 10^8 m/s

v = frequency in hz (1/s) ← seconds

Atomic Absorption and Emission Line Spectra

When electromagnetic radiation is passed through a collection of atoms, some of the radiation is absorbed and used to excite the atoms from a lower energy level to a higher energy level.

An emission spectrum is produced by atoms emitting photons of light when electrons in excited states return to lower energy levels

The Hydrogen Spectrum

The line emissions spectrum of hydrogen provides evidence for the existence of electrons in discrete energy levels, which converge at higher energy levels

The hydrogen atom gives out energy when an electron falls from a higher energy level to a lower energy level. Hydrogen emits visible light when the electron falls to the second energy level (n=2)

The lines converge at higher energies because the energy levels inside of the atom are closer together at higher energy. When an electron reaches the highest energy level (n = ∞), the electron leaves the atom and results in an ion.