4.1.1.3 - The development of the model of the atom

What can lead to a scientific model being changed or replaced?

New experimental evidence may lead to a scientific model being changed or replaced

What were atoms thought to be before the discovery of the electron?

Before the discovery of the electron, atoms were thought to be tin, solid spheres that could not be divided.

(John Dalton also said that different spheres made up different elements)

What model did the discovery of the electron lead to?

The discovery of the electron led to the plum pudding model of the atom - by J.J Thomson

Describe the plum pudding model.

The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.

Who proposed the plum pudding model?

J.J. Thompson

Who conducted the alpha scattering experiment?

Ernest Rutherford and his team

What conclusion did the alpha scattering experiment lead to?

The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was (positively) charged.

After this experiment, what model replaced the plum pudding model?

The nuclear model

A tiny, positively charged nucleus surrounded by a cloud of negative electrons

How did Niels Bohr adapt the nuclear model?

Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances (in energy shells)

The theoretical calculations of Bohr agreed with experimental observations.

What did later experiments lead to the idea of?

Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge.

The name proton was given to these particles.

Who provided the evidence to show the existence of neutrons in the nucleus?

James Chadwick

This was about 20 years after the nucleus became an accepted scientific idea