Atomic structure

Over 100 years ago, it was thought the atomic structure looked similar to a plum pudding.

It was thought that atoms were spheres of positive charge with tiny electrons stuck in them.

The plum pudding theory was changed not long after it was made. In 1909, Rutherford and Marsden tried firing a beam of alpha particles into a layer of thin gold foil. 

The alpha particles went through the sheet and a few was deflected but majority went through the sheet. This suprised the two as they thought all of the alpha particles would bounce off. 

This showed that most of the mass of an atom was concerntrated at the centre in a tiny nucleus. They also realised it must have a large positive charge, since it repelled the positive alpha particles.

It also showed the atom is just an empty space.

The nucleus is tiny but it makes up most of the mass of the atom. It contains protons (which are positively charged) and neutrons (which are neutral) which gives and overall positive charge.

The rest of the atom is space.

The negative electrons whizz around the outside of the nucleus really fast.

Particle        Mass        Charge

Proton           1                 +1

Neutron         1

Electron

The nucleus is tiny but it makes up most of the mass of the atom. It contains protons (which are positively charged) and neutrons (which are neutral) which gives and overall positive charge.

The rest of the atom is space.

The negative electrons whizz around the outside of the nucleus really fast.

Particle        Mass        Charge

Proton           1                 +1

Neutron         1                  0

Electron      1/200              -1

The number of protons is the same of the number of electrons

Atoms have no charge

The charge on an electron is the same size as the charge on a proton - but opposite

This means the number of protons always equals the number of electrons in a neutral atom

If some electrons are added or removed, the atom becomes a charged particle called an ion.