Models in physics and beyond are used to describe or explain a challenging concept in a more visual or tangible way (e.g. the brain is like a library, electric current is like water flow). The atomic model is the best guess we currently have that explains our encounters with particles everyday.
In the IB course there are few surprises; the experiments you are required to conduct usually verify the theory. However, when Rutherford saw the results of the alpha particle scattering experiment, he was very surprised. The results were not in line with the theory and led to a new visualisation of the atom. Science has often developed out of surprise results.
Nucleus
The Thomson model of the atom had the following key ideas:
- A solid lump of homogeneous positive charge (the "pudding")
- Small negative regions located randomly throughout (the "plums")
- Neutral overall
This model explained the existence of discrete particles of negative charge (electrons) but was proved wrong by Rutherford.
Electrons and quantum
So far we have considered light to behave as a wave. However, light also behaves as discrete quantised particles (photons) in certain experiments. Energy and wavelengths of light are linked mathematically so that specific wavelengths correspond to specific energies:
\(E=hf\) and \(E={hc\over \lambda}\)
- E = energy of a photon (J)
- h = Planck's constant (\(6.63 \times 10^{-34}\) m2 kg s-1)
- f = frequency of light (Hz)
- c = speed of light (\(3\times 10^8\)ms-1)
- λ = wavelength of light (m)
How much of Atomic models have you understood?