Electromagnetic Radiation and Atomic Spectra

Electromagnetic radiation behaves like both waves and particles, which scientists call its "dual nature". When this radiation interacts with matter, it comes in packets called photons - think of them as tiny energy bullets that atoms can absorb or release.

The key thing to remember is that wavelength (measured in metres or nanometres for visible light) and frequency (measured in Hz) determine how much energy a photon carries. Higher frequency means more energy - that's why UV light can damage your skin whilst radio waves can't.

Here's the maths you need: E = hf gives you the energy of a single photon, where h is Planck's constant and f is frequency. For a whole mole of photons, just multiply by Avogadro's number: E = Lhf. You can also use wavelength with E = hc/λ.

Quick Tip: The speed of light $c$ is always 3×10⁸ ms⁻¹ - memorise this constant as you'll use it loads in calculations.

When atoms absorb electromagnetic radiation, their electrons get promoted to higher energy levels - they become "excited". This process creates absorption spectra, which show up as dark lines where specific wavelengths have been absorbed. Conversely, emission spectra appear when excited electrons fall back down and release photons as coloured lines.

The brilliant thing about spectra is that each element produces its own unique pattern - like a fingerprint. This means scientists can identify unknown elements just by looking at their spectral lines, whether it's analysing a sample in the lab or determining what stars are made of millions of miles away.