Developing the model of the atom

Atom

Building block of matter

J J Thomson

Discovered the electron and went on to propose that the atom looked like a plum pudding

Plum Pudding model

An atom is a sphere of positive charge, with negatively charged electrons in it

Ernest Rutherford

Conducted an experiment to test the plum pudding model

Alpha particle scattering experiment

An experiment carried out by two students of Ernest Rutherford where they directed a beam of alpha particles at a very thin gold foil suspended in a vacuum

Alpha particles

A type of nuclear radiation with a positive charge

Expected results from experiment

The alpha particles should have passed straight through the foil undeflected

Actual results from experiment

Most of the alpha particles did pass straight through the foil but a small number of were deflected by large angles and a very small number of alpha particles reflected straight back off the foil

conclusions from experiment

the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged

Nuclear model

An atom is mostly empty space with a positively charged nucleus in the centre that contains most of the mass and electrons orbiting the nucleus

Niels Bohr

Adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances

James Chadwick

Provided the evidence to show the existence of neutrons within the nucleus

Current model of the atom

An atom is mostly empty space with protons and neutrons contained in the nucleus and electrons orbiting the nucleus in different energy levels

What happens to electrons when an atom absorbs energy

Electrons at a particular energy level jump to higher levels (at larger distances from the nucleus)

When electrons in an atom move to a lower energy level

The atom emits energy, releasing it as a specific frequency of light