Energy levels in atoms and line spectra (22.4)

What values of electron energy levels are there in isolated atoms?

In isolated atoms, the electron energy levels are discrete (there are only certain values of energy they can have)

Why are there discrete electron energy levels in atoms?

There are a number of discrete wavelengths in an atom (as orbitals are standing waves). Each wavelength is associated with a discrete change in energy. This difference between energy levels implies discrete energy levels.

How can the electron energy levels be represented?

Electron energy levels can be represented in an energy level diagram:

Where the most negative level is the ground state

What is the consequence of the electron energy levels being discrete?

Only photons/electrons of certain energies can be absorbed and these energies must equal the difference in energy between 2 energy levels

How can electrons be ionised in terms of energy levels?

1) If a photon is absorbed that has a higher energy than the difference between the ground state and the highest energy level

2) If a free electron collides that has a higher kinetic energy than the difference between the ground state and the highest energy level

If the photon/electron have excess energy its given to the freed electron as kinetic energy

How can electrons de-excite in terms of energy levels?

The atom de-excites immediately after excitation, by emitting one or more photons, each equal to the difference in two energy levels

When electrons de-excite, how are the photons emitted?

The photons are emitted in random directions

What are emission line spectra and how is it formed?

Emission line spectra - bright, coloured lines on a dark background

They are formed as electrons are excited by the photons from the hot gas. When they de-excite they emit photons, which corresponding with wavelengths and thus specific colours, shown in the spectrum.

What are absorption line spectra and how are they formed?

Absorption line spectra - dark lines on an otherwise continuous spectrum

They are formed as white light passes through a cool gas of atoms, certain energy photons are absorbed, corresponding to specific colours. When the electrons de-excite they release photons in random directions, leading to certain colours being removed.