Atoms, mixtures and the atomic model

The idea

An element contains one type of atom; a compound contains two or more elements chemically combined; a mixture contains substances not chemically combined, which can be separated by filtration, crystallisation, distillation, fractional distillation or chromatography. The model of the atom changed with evidence: Thomson's plum pudding, then Rutherford's alpha scattering experiment showed a small, dense, positive nucleus; Bohr placed electrons in shells; Chadwick discovered the neutron. Relative charges: proton +1, neutron 0, electron −1.

1. Decide: element, compound or mixture.
2. Choose the separation method by the property that differs.
3. Link each model to the evidence that replaced it.

Watch out In the alpha scattering experiment, most particles passed straight through: so most of the atom is empty space.