4.4.1.3 - The development of the model of the atom

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

New experimental evidence can 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 tiny, solid spheres that could not be divided

What model did the discovery of the electron lead to?

The plum pudding model

Who proposed the plum pudding model?

J.J Thompson

Describe the plum pudding model.

Plum pudding model stated that the atom was a ball of positive charge with negative electrons embedded in it

What did Rutherford conduct in 1909?

In 1909, Rutherford conducted the alpha scattering experiment

What results did Rutherford expect to obtain?

Rutherford expected the particles to pass straight through the gold sheet

Or to only be slightly deflected

However, what results did Rutherford actually obtain?

However, some particles were deflected more than he has expected and some were even deflected back the way they had come

What model did the Alpha scattering experiment lead to?

To the nuclear model of the atom

Describe this nuclear model of the atom.

The atom was mostly empty space

That most of the atom’s mass was concentrated in a positively charged nucleus

This is then 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 - called energy levels / shells

What idea concerning the positive charge of the nucleus arose after later experiments?

Later experiments led to the idea that the positive charge of the nucleus could be subdivided into a whole number of smaller particles

Which were called protons

What did James Chadwick prove?

James Chadwick provided the evidence to show the existence of neutrons within the nucleus

How long after the nucleus became an accepted scientific idea did James Chadwick prove the existence of neutrons?

20 years after the nucleus became ac accepted scientific idea