Ionisation & Excitation
- Electrons in an atom occupy certain energy states called energy levels
- Electrons will occupy the lowest possible energy level as this is the most stable configuration for the atom
- When an electron absorbs or emits a photon, it can move between these energy levels, or be removed from the atom completely
Excitation
- Excitation is:
When an electron absorbs enough energy to move up to a higher energy level
- When an electron moves to a higher energy level, the atom is said to be in an excited state
- To excite an electron to a higher energy level, it must absorb a photon
- Electrons can also move back down to a lower energy level by de-excitation
- To de-excite an electron to a lower energy level, it must emit a photon
Ionisation
- Ionisation is:
When an atom gains or loses an orbital electron and becomes charged
- When an electron is removed from an atom, the atom becomes ionised
- An electron can be removed from any energy level it occupies
- However, the ionisation energy of an atom is the minimum energy required to remove an electron from the ground state of an atom
Fluorescent Tube
- Fluorescence occurs when an electron in an atomic orbital absorbs energy from an interaction with a photon or a collision with another electron
- Fluorescent tubes are partially evacuated glass tubes filled with low-pressure mercury vapour with a phosphor coating on the glass
Fluorescent tubes operate on the basis of excitation and de-excitation of electrons leading to the emission of visible light
- When a high voltage is applied across the tube, electrons flow from the cathode to the anode producing an electron beam
- These beam electrons collide with the electrons in the mercury atoms transferring kinetic energy in the collision
- The atomic electrons in the mercury atoms are excited and move to a higher energy level
- This high energy level state is unstable and so the electrons de-excite i.e. move back to their original ground state
- As they de-excite, the electrons release that energy by emitting photons in the UV range of wavelengths
- The UV photons then collide with electrons in the atoms of the phosphor coating and excite them into a higher energy level
- As these phosphor electrons de-excite, they do so in stages emitting photons in the visible light range of wavelengths
