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Atomic Spectra
Atoms can become excited by absorbing energy.

Atoms in their ground state have all their electrons at their lowest possible energy levels.

Ground state When the electrons in an atom are all at their lowest
possible energy levels

If an atom's electrons take in energy from their surrounding…

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Absorption Spectra
Energy is related to frequency.

So when electromagnetic radiation is passed through a gaseous element, the electrons only
absorb certain frequencies, corresponding to differences between the energy levels.

That means the radiation passing through has certain frequencies missing.

A spectrum of this radiation is called an atomic absorption…

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Emission Spectra
When electrons drop to lower energy levels, they give out certain amounts of energy.

This produces lines in the spectrum.

The emission spectrum has a black background with coloured lines on it.

For any particular element, the frequencies in an emission spectrum are the same as those

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Bohr's Theory
The basic idea behind Bohr's theory was:

Atomic spectra are caused by electrons in atoms moving between different energy
When an atom is excited, electrons jump into higher energy levels again ­ and emit
the extra energy as electromagnetic radiation, which gives an emission spectrum.

Bohr's theory…

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The rings represent the energy levels of the electron
in the hydrogen atom.

The further away from the nucleus an electron is, the
higher the energy level.

Energy levels are labelled with numbers, starting at 1
for the lowest level ­ the ground state.

The frequencies of the lines correspond…




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