Development of the model of the atom

Dalton’s model

The 1st model. Did not include protons, electrons or neutrons.

The Plum Pudding Model

2nd model. Electrons are discovered leading to the idea that they were in a cloud of positive charge

Alpha Scattering Experiment

1. Scientists fired small positively charged particles at a piece of gold foil

2. They expected alpha particles to travel through the gold

3. They were surprised when some of the particles bounced back (alpha scattering)

4. Scientists suggested that the positive charge and mass of an atom was found in the centre, they called this the nucleus

Nuclear model

3rd model. Replaced plum pudding and suggested that electrons orbit the nucleus but NOT at set distances

Electron shell (Bohr) model

4th model. Neils Bohr calculated that the electrons must orbit at set distances, these are called shells or energy levels.

The proton

Further experiments proved that the nucleus contains protons which have an opposite charge to an electron.

The neutron

James Chadwick carried out experiments that signalled there was a particle with no charge. This was called neutrons and located in the nucleus.

Relative mass

Proton- 1

Neutron- 1

Electron- 0

Size

Radius of 1×10 to the power of -10.