Electrons and the Electrons and the Visible SpectrumVisible Spectrum

In the Bohr model it was the In the Bohr model it was the existence of colour that showed existence of colour that showed there were different energy levels. there were different energy levels.

Ground state – the lowest energy Ground state – the lowest energy state of an electronstate of an electron

Excited state - an electron at a high Excited state - an electron at a high higher level than the ground state.higher level than the ground state.

Colour and Metal IonsColour and Metal Ions

When heat or electricity is added to a When heat or electricity is added to a metal some of the electrons become metal some of the electrons become excited and leave the ground state to excited and leave the ground state to jump to a higher energy level.jump to a higher energy level.

The electrons will eventually fall back The electrons will eventually fall back to their ground state and will release to their ground state and will release their energy either as heat or light. their energy either as heat or light.

The frequency of this released energy The frequency of this released energy determines the colour we see. determines the colour we see.

The larger the jump (and fall) the The larger the jump (and fall) the higher the frequency we see. A low higher the frequency we see. A low frequency light may be produced by frequency light may be produced by a fall from the 2a fall from the 2ndnd level to the 1 level to the 1stst and and a high frequency may be produced a high frequency may be produced with a fall from the 6with a fall from the 6thth level to the level to the 22ndnd. .

I R I R R R O O Y Y G G B B I I V V UV UV

Low frequency High Frequency Low frequency High Frequency

ExamplesExamples

FireworksFireworks

Flares Flares

Light Bulb –Light Bulb –

(Tungsten)(Tungsten)

Fire Logs - Fire Logs -

Neon Signs –Neon Signs –

Street Lights –Street Lights –

(Sodium Lamp) (Sodium Lamp)

Mercury Vapour LampMercury Vapour Lamp