Dalton
- an atom is the smallest building block of an element
- they cannot be divided any further
- 1 x 10-10 m
JJ-Thompson
- Plum pudding model
- He discovered the electron
- He thought the atom was made up of
- negatively charged electrons (plums) in a positively charged ‘pudding’
Rutherford's alpha scattering experiment
- Geiger and Mersden conducted the experiment
- They fired alpha particles at a gold sheet
Observations
- Most particles went straight through
- Only some deflected or reflected
Conclusions
- Only deflected when it hit the nucleus - all mass is condensed in the nucleus
- Most of the atom is empty space
Bohr
- said that electrons orbit in fixed shells
Chadwick
- proved the existence of the neutron