C1, P1, history of atom, alpha scattering experiment

How did the discovery of electrons change the atomic model?

Electrons were discovered in 1897. This showed atoms had internal structure, so scientists developed the plum pudding model.

Describe the plum pudding model of the atom.

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

Describe the alpha scattering experiment.

1. Fire positively charged alpha particles at thin gold foil. 2. Observe how the particles pass through, deflect or bounce back.

What did scientists observe in the alpha scattering experiment?

Most alpha particles passed straight through; some were deflected; a very small number bounced straight back.

Why gold foil?

You can hammer gold into very thin foil- just a few atoms thick.

What did each result of the alpha scattering experiment show?

Most passed through: atoms are mainly empty space. Some deflected: the centre is positively charged. (as alpha particles positive- if any come to positive centre of an atom is repelled) Very few bounced back: the centre contains most of the atom’s mass.

Why did the alpha scattering experiment disprove the plum pudding model?

The results showed that positive charge and most of the mass are concentrated in a tiny central nucleus, rather than spread throughout the atom. - it was replaced with nuclear model.

Describe the nuclear model of the atom.

Atoms are mainly empty space, with a tiny, positively charged nucleus containing most of the mass and negative electrons around it.

How did the nuclear model differ from the plum pudding model?

The plum pudding model had positive charge spread throughout the atom. The nuclear model has a tiny positive nucleus containing most of the mass, with electrons around it.