Electromagnetic radiation and atomic spectra

Electromagnetic radiation

Can be described in terms of waves and characterised by wavelength and/or frequency

Wave equation

The relationship between speed

Electromagnetic spectrum

The arrangement of different types of radiation in order of wavelength

Visible light wavelength units

Normally expressed in nanometres (nm)

Dual nature of electromagnetic radiation

Can be described as both a wave and a particle

Photons

Particles of electromagnetic radiation that carry quantised energy

Photon energy

Proportional to the frequency of radiation

Energy transfer by photons

Occurs when photons are absorbed or emitted and electrons gain or lose energy

High frequency photons

Transfer greater amounts of energy than low frequency photons

Energy of a photon

Given by E = hf or E = hc/λ

Energy of a mole of photons

Given by E = Lhf or E = Lhc/λ

Energy units

Often expressed in kJ mol⁻¹

Electron excitation

Occurs when atoms absorb energy and electrons are promoted to higher energy levels

Electron relaxation

Emits a photon as an excited electron returns to a lower energy level

Atomic emission spectra

Series of lines at discrete energy levels showing evidence of quantised energy levels

Element identification

Each element produces characteristic absorption and emission spectra

Absorption spectroscopy

Electromagnetic radiation is absorbed by electrons promoted to higher energy levels

Absorption spectrum

Produced by measuring how absorbed light intensity varies with wavelength

Emission spectroscopy

High temperatures excite electrons

Emission spectrum

Produced by measuring the intensity of emitted light at different wavelengths

Atomic spectroscopy

The concentration of an element in a sample is related to the intensity of light emitted or absorbed