What happens when a high energy electron collides with an electron in the ground state?

The incoming electron transfers energy to the electron in the ground state, causing it to move to a higher energy level. 

This process is known as excitation.


The energy transferred to the ground state electron will be equal to the difference between the ground state energy level and the destination energy level.

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How can an electron become excited?

  1. An incident electron transfers energy to an electron in an energy level.
  2. An incident photon transfers all it's energy to an electron in an energy level.

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Define the term ionisation energy.

Ionisation energy is the minimum energy required to remove an electron from the ground state.

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What happens when an electron de-excites?

A photon is released with an energy equal to the difference between the starting and destination energy levels.

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What is meant by discrete energy levels?

Electrons can only exist in well defined energy levels that have fixed values. 

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What is meant by the term one-to-one interaction?

A single photon or electron transfers energy to a single electron in the atom.

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Describe what happens when a photon is incident on an electron in the ground state.

If the energy of the photon is equal to the difference between the ground state and another energy level, the electron will become excited. 

When this happens the photon ceases to exist. 


If the photon energy does not match the difference between the ground state and another energy level, no interaction will occur.

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Explain using the idea of energy levels how fluorescent bulbs works.

  1. An incoming high energy electron causes the mercury vapour to become excited.
  2. When the mercury de-excites it emits a photon in the UV region.
  3. The fluorescent coating absorbs the UV photon and becomes excited.
  4. When the fluorescent coating de-excites, it emits photons in the visible region.

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Why are all energy levels negative?

At the point of ionisation an electron has zero kinetic energy.

Energy is input to get an electron to be ionised, lower energy levels have negative values.

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