Collisions of Electrons with Atoms

• What do electrons in an atom occupy?

  Energy levels
• Why do electrons occupy the lowest possible energy level?

  It is the most stable configuration
• What happens when an electron absorbs or emits a photon?

  It can move between energy levels
• What is excitation in terms of electron energy levels?

  When an electron moves to a higher energy level
• What state is an atom in when an electron is excited?

  Excited state
• What must an electron do to move to a higher energy level?

  Absorb a photon
• What occurs during de-excitation of an electron?

  The electron moves back to a lower energy level
• What must an electron do to de-excite to a lower energy level?

  Emit a photon
• What is ionisation?

  Gaining or losing an orbital electron
• What happens when an electron is removed from an atom?

  The atom becomes ionised
• From which energy level can an electron be removed?

  Any energy level it occupies
• What is the ionisation energy of an atom?

  Minimum energy to remove an electron
• What occurs during fluorescence?

  An electron absorbs energy and emits light
• What are fluorescent tubes filled with?

  Low-pressure mercury vapour
• How do fluorescent tubes operate?

  Based on excitation and de-excitation of electrons
• What happens when a high voltage is applied across a fluorescent tube?

  Electrons flow from cathode to anode
• What do beam electrons do in a fluorescent tube?

  Collide with electrons in mercury atoms
• What happens to atomic electrons in mercury atoms during collisions?

  They are excited to a higher energy level
• What occurs when excited electrons in mercury atoms de-excite?

  They emit photons in the UV range
• What do UV photons do in a fluorescent tube?

  Excite electrons in the phosphor coating
• What happens as phosphor electrons de-excite?

  They emit photons in the visible light range