Chapter 3: Electrons and energy levels Flashcards
What is a photon?
A discrete packet (quantum) of electromagnetic energy
What is an electron volt?
A unit of energy equal to 1.6x10-19 J. It is the energy gained by an electron when it is accelerated through a potential difference of 1 volt.
What is an energy level?
Defined and distinct energies at which electrons can exist in an atom. They are quantised energy levels as they have fixed energy values. An electron cannot exist between energy levels.
What is the ground state?
The lowest energy level an electron can be in (and the most stable)
What is excitation?
The process of an electron taking in exactly the right quantity of energy to move to a higher energy level.
What is ionisation?
When an atom loses or gains an electron and becomes charged
What is a continuous spectrum?
A spectrum where all frequencies of radiation or colours of light are possible
What is a line spectrum?
A spectrum of discrete coloured lines of light
What is an emission spectrum?
A bright spectrum seen when photons are emitted by atoms (caused by de-excitation)
What is an absorption spectrum?
A spectrum of dark lines seen on a coloured background produced when a gas absorbs photons
What is the equation for energy relating to energy levels?
hf= E2 - E1
En: energies of energy levels
What is a fluorescent tube?
A type of light bulb that gives out light when its inner coating fluoresces
What is thermionic emission?
The release of free electrons from a heated filament
How does a fluorescent tube work?
-Glass tube filled with mercury vapour and coated with fluorescent phosphor dyes.
-When switched on, cathode is heated causing thermionic emission and a p.d of 500V is applied across the ends of the tube, accelerating the electrons through the mercury vapour.
-The electrons collide with atoms which become ionised or excited. Electrons then return to their ground state, releasing UV photons.
-UV photons strike the phosphors, are absorbed causing excitation before they cascade and return to their ground state, releasing multiple photons including photons of visible light.
