Electromagnetic Radiation
Definition and meaning of Electromagnetic Radiation in chemistry.
Electromagnetic radiation is energy that propagates through space as coupled, oscillating electric and magnetic fields, traveling at the speed of light and requiring no medium.
In more detail
It behaves both as a wave, described by wavelength and frequency, and as a stream of discrete energy packets called photons, with each photon's energy given by E = hν (h is Planck's constant, ν is frequency). The electromagnetic spectrum ranges from low-energy radio waves through microwaves, infrared, visible light, and ultraviolet, to high-energy X-rays and gamma rays. In chemistry, this radiation is central to spectroscopy and photochemistry, because atoms and molecules absorb or emit only specific photon energies that match the spacing between their quantized electronic, vibrational, or rotational energy levels.
Key facts
| Field | Physical Chemistry |
|---|---|
| Speed in vacuum | c = 2.998 × 10^8 m/s |
| Energy-frequency relation | E = hν |
| Spectrum range | radio waves to gamma rays |
Visible light between roughly 400 and 700 nm is absorbed by chlorophyll molecules in plants, exciting electrons to higher energy levels and driving the light reactions of photosynthesis.
Frequently asked questions
How are wavelength and photon energy related?
They are inversely related through E = hc/λ, so shorter-wavelength radiation (like UV or X-rays) carries more energy per photon than longer-wavelength radiation (like radio waves).
Why doesn't electromagnetic radiation need a medium to travel?
Unlike mechanical waves such as sound, it consists of self-propagating electric and magnetic field oscillations, so it travels through a vacuum, which is why sunlight reaches Earth through space.