History of Atomic Theory

Question 1

Dalton 1803

Answer 1

Atoms are hard spheres.
Different elements are made of different atoms.
Compounds are when elements combine.

Question 2

JJ Thompson 1904

Plum Pudding Model

Answer 2

An atom is a bass of positive charge studded with negative electrons.

Question 3

Rutherford 1910

Nuclear Model

Answer 3

The positive charge is in a nucleus at the centre of the atom.
The nucleus contains the mass of the atom.
Electrons are all around the outside of the nucleus
Most of the atom is empty space.

Question 4

Bohr 1913

Planetary Model

Answer 4

The electrons are in shells.

The shells are fixed distances from the nucleus.

Question 5

Chadwick 1932

Discovery of the neutron

Answer 5

Discovered later than other subatomic particles as it is not charged therefore hard to detect.
This is another example of scientists changing their opinions based on evidence: the neutron explained why isotopes had different masses.