Flame tests

Where does light come from? It all starts with ATOMS A nucleus surrounded by electrons that orbit.

Bohr’s Model of the Atom Planetary model of the atom. Nucleus with protons and neutrons. Electrons orbiting the nucleus.

Where does light come from? Like the planets in the solar system, electrons stay in the same orbit, unless… Electrons get kicked into a different orbit This doesn’t happen very often in solar systems, but it does in atoms If you add energy to an atom (heat it up), the electrons will jump to bigger orbits. When atom cools, electrons jump back to original orbits. As they jump back, they emit light, a form of energy

Energy levels

Quantum Jump!

Therefore the light given out when atoms were heated always have specific amounts of energy. It was Bohr in his study of light that suggested that the electrons must be orbiting the nucleus in fixed energy levels or shells.

Colour of light Energy Each electron that jumps back emits one photon of light What colour is this light? Depends on how big the jump between orbits was The bigger the jump, the higher the energy. The energy determines color; a blue photon has more energy than a red

Excited states are unstable Excited states are unstable. Electrons quickly falls back to the ground state, but not always in a single step. For example, if the electron is initially promoted to the n=3 state, it can decay either to the ground state or to the n=2 state, which then decays to n=1.

Flame Test Colour Colour seen is a result of different wavelengths of light (colours) emitted when the electrons go down the step(s) to their ground state. Each element will have its own set of steps, therefore each will have its own colour. Some colours are very similar so a more exact method can be used to identify the elements.

Emission Spectrum Hydrogen

Light as particle A photon is like a particle, but it has no mass Think of a photon as a grain of sand. We see so many photons at the same time it’s like seeing all the sand on a beach; we don’t notice the single grains When light hits film in a film camera, it acts like photons.