The Electromagnetic Spectrum (College Board AP® Chemistry): Revision Note

The Electromagnetic Spectrum

• The electromagnetic spectrum is a range of frequencies that includes all wavelengths of electromagnetic radiation

• The spectrum connects three important variables in the study of light: frequency, wavelength and energy

  • Wavelength is the distance between two consecutive crests on a wave

  • Frequency (ν) is the number of waves that pass a point each second (unit s^-1)

• Higher-energy radiation has a shorter wavelength and a higher frequency

  • High-frequency radiation (ultraviolet, X-rays and gamma rays) carries enough energy per photon to damage living cells

The electromagnetic spectrum diagram

The electromagnetic spectrum runs from long-wavelength, low-energy radio waves to short-wavelength, high-energy gamma rays

• All electromagnetic waves travel at the same speed in a vacuum, c; they differ in frequency and wavelength, and so in the energy of each photon

• The speed of light (c) is a constant: 2.998 × 10⁸ m s^-1 (the value in the equations and constants reference available in the exam)

• Molecules behave in particular ways when they are exposed to radiation of different frequencies

  • When exposed to microwaves, molecules will rotate

  • When exposed to infrared radiation, molecules will vibrate

  • When exposed to ultraviolet or visible radiation, the electrons will jump between energy shells