Alpha scattering experiment

What did ancient Greeks believe

Everything is made of atoms

Atoms are tiny spheres that cannot be divided

When was electron discovered

1897

JJ Thomson

Significance of electron discovery

Shower that atoms are not spheres that cannot be divided. Atoms have an internal structure

What was the plum pudding model

An atom is a ball of positive charge with negative electrons embedded in it

How did scientists try to test the plum pudding model

By conducting thre alpha scattering experiment

What was the alpha scattering experiment

Scientists took a thin sheet of gold foil. Then fired alpha particles (positive charge) at the gold foil

Results of the alpha

Most of the alpha particles went straight through the gold foil, therefore atoms are mostly empty space

Some of the alpha particles were deflected, therefore the centre of an atom must have a positive charge and that repelled the alpha particles

Some alpha particles bounced straight back, therefore the mass of the atom must be concentrated in the centre (nucleus)

What did scientists replace the plum pudding model with

The nuclear model

Describe nucleur model

Most of atom is empty space

Tiny centre called nucleus which contained most of the mass

Electrons surrounded it around the edge

What did Niels Bohr state

Electrons orbit the nucleus at specific distances

His work agreed with the results of other scientists

We now cal these shells

When were protons discovered

Ernest Rutherford

1919

When we’re neutrons discovered

James Chadwick

1932