The Atom Models Through Time

Question 1

Dalton’s Model

Answer 1

JOHN DALTON - 1803
Atom as a solid sphere which is indivisible.
Extra info: atomos = indivisible in Greek

Question 2

Plum Pudding Model

Answer 2

J.J THOMPSON - 1904
Discovered electrons - electrons are scattered throughout spherical cloud of positive charge.

Question 3

Nuclear Model

Answer 3

Ernest Rutherford - 1911
Electrons orbit the positively charged centre (nucleus) with positive particles aka. protons, although not at set distances.

See Alpha Scattering Experiment in 1909 to see how he proved.

Question 4

Niels Bohr’s Model

Answer 4

1913 - modified and developed Rutherford’s model.

Calculated that electrons must orbit the nucleus at fixed distances called electron shells or energy levels.

Question 5

James Chadwick’s Model

Answer 5

1932 - Discovered neutrons.
Chadwick carried out experiments that gave evidence for the existence of additional mass that juxtaposed the charge of the atom which previously confused scientists who got ‘inaccurate’ results. However, Chadwick founded the existence of a particle in the nucleus that had no charge but still had mass (relatively the same as protons)

Question 6

Alpha Scattering Experiment

Answer 6

1909 - Rutherford
1. Fired small positively charged particles (ALPHA PARTICLES) at a piece of gold foil.
Although they expected the atoms to travel through the gold, some were repelled - known as ALPHA SCATTERING.
2. Suggested that positive alpha particles were repelled by another positive charge existing in the gold atoms.
3. Concluded that positive charge in an atom was concentrated in the centre - a nucleus of protons. Therefore, apart from the spaced out electron’s orbiting shells, atoms are mostly made up of empty space.

Ernest Rutherford is credited for the discovery of protons and early stages of understanding subatomic particles.