Explaining The Flame Colour

Explain the flame colour in terms of electrons releasing energy as they move to a lower energy level


  • Light or electromagnetic (EM) radiation both waves and particulate properties, have different types such as, gamma rays, x-rays, ultra-violet (UV) rays, visible light, infra-red (IR), microwaves and radiowaves (TV/ FM/AM)\
  • When light strikes an object, it can be absorbed, reflected or only particular wavelengths is absorbed and the rest is transmitted/reflected.
  • Waves are characterized by:
    • Wavelength: distance between two successive waves
    • Frequency: number of cycles per second that pass a given point in time

v = c/Δ

where   v –  frequency (in Hertz or s-1)

Δ – wavelength (in meter)

c – speed of light (3 x 108 m/s)

  • Human eye is sensitive to the visible region of the EM spectrum
    • Beyond red end = Infra-Red region
    • Beyond Blue end = Ultraviolet region
  • Different frequencies of visible light = different wavelengths of visible light = varying observed colours
    • Frequency (v) is directly proportional to energy of photon (E), however inversely proportional to wavelength (λ)

E = hv = h c/Δ

  • High frequency waves = High energy of Photon= Low wavelength
  • Light given off by energetically excited atom is not a continuous distribution of wavelength
  • Each element has its own unique spectral signature

Flame Colour of Elements:

  • Flame colour is produced when a granule of ionic compound or a drop of its solution are placed in a flame
  • Some of the commonly known metallic elements have known to strongly emit light in the visible region of EM spectrum
  • Through absorbing or emitting discrete amount of energy (quantized energy called photons), electrons are able to move to different orbits
  • Once an electron becomes excited (electron in higher energy level), photons are released after it reached the ground state (electron in original energy level ) resulting to the formation of spectral line (wavelength of light)
    • The wavelength which is associated to the observed colour is dependent on the change in energy level and orbit of the electron
    • The colour exhibited/reflected by an object is explained as that:
  • All wavelengths of white light that strikes through a substance are absorbed except for a particular wavelength which is consequently reflected

Example: For a given material, all wavelengths of visible spectrum are absorbed except for yellow wavelength (reflected) upon contact with white light, thus yellow colour is observed.

  • When a substance absorbs a particular wavelength from white light that passed through, the complementary wavelength to the absorbed specific wavelength is reflected or observed

Example: Blue absorbed = Orange observed