July 5, 2021
The history included in I/GCSE Chemistry
Dalton
- His theory was that atoms where solid spheres.
- The different spheres represented the different elements.
Thomson
- J.J. Thompson developed Dalton's theory using the Plum Pudding Model.
- This model was the idea of a positively charged sphere with fixed negatively charged electrons as he concluded that there was smaller negatively charged particles from his measurements of mass and charge.
Rutherford
- He tested this theory with the Gold Foil Shattering Experiment.
- Rutherford shot positive alpha particles at thin gold foil expecting that the particles would reflect slightly and most go directly through the foil.
- However, this wasn't the case; the particles either went through the foil, were reflected at extreme angles or even repelled back.
- This concluded that the Plum Pudding Model was incorrect.
- He created the Atomic Model which consisted of a 'cloud' of electrons surrounding a nucleus.
Bohr
Bohr thought this model was incorrect as the atom would just collapse if the electrons where a 'cloud' surrounding the nucleus.
He developed the Atomic Model with the electrons being in shells orbiting the nucleus, the electrons stayed in these fixed shells and there was gaps in between them.
Chadwick
- With experiments by Rutherford and others, they discovered that the nucleus was divided into smaller parts - they discovered the positive protons.
- 20 years after this discovery, Chadwick did experiments which proved that there were neutral parts to the nucleus too. These are neutrons.
- The closest model we use to the present day is Chadwick's Nuclear Model.
Written by Bryant Wong (Chemistry)