A gas atom when excited by heating or passing an electron through discharge tube, gives off light. The light emitted is characterised by specific wavelength and frequency, and this is called line spectra.
A series of line spectra are produced depending on the nature of the substance.
Types of Spectra
There are two types of spectra namely: emission spectra and absorption spectra.
1. Emission Spectra
Electron moving from a higher energy level to lower energy level produces emissions spectra. There are three types of emission spectra namely:
- Line Spectra: This consists of lines of different colours, with well defined lines each having a particular frequency or wavelength. It is produced by excited atoms from burning gases.
- Continuous Spectra: Consists of light of all colours or wavelength e.g. incandescent solid tungsten lamp. The atoms in the metal are closely parked together, the individual energy level merge together, hence the emitted lines overlap and form a continuous spectrum.
- Band Spectrum: Consists of bands with each band composed of series of lines close together at one end and farther apart at the other end. Oxygen gas and Co2 produces band spectrum.
2. Absorption Spectra
This occurs when light passes through a cool gas and certain wavelength of light are absorbed, which give series of dark lines each corresponding to one of the wavelength absorbed. Investigation revealed that each element absorbs exactly those wavelength they emit, when they are hot.