RUTHERFORD’S EXPERIMENT

How he found out how atoms were put

together

In 1911 it was known that things were made from atoms, and that atoms had positive (+) and negative (-) charges.

They thought that atoms were solid little balls of

positive charge, with even smaller electrons of

negative charge stuck in them.

This was the “Plum Pudding” model

Spread out positive charge

Electron (negative charge)

In 1911 Rutherford designed an experiment to

find out about the structure of an atom. He fired alpha particles at a very thin piece of gold

leaf.

gold leaf

detector

alpha particles

He expected them all to go straight through…….

gold leaf

detector

alpha particles

But some bounced straight back………….

gold leaf

detector

alpha particles

And some were deflected………….

From this he worked out two things……..

1. Atoms were mostly empty space apart from a

solid centre, or nucleus.This is why some particles bounced back.

Empty space

Solid nucleus

2. The nucleus has a positive charge, which is

why the positively charged alpha particles are

repelled if they get too close.

Empty space

Solid nucleus

Repelled by positively charged nucleus

If the nucleus has all the positive charge, then the

negatively charged electrons must be away

from the nucleus.

This is how we get Rutherford’s model of the

atom

Electron (negative charge)

Positive charge concentrated at the centre