Atomic Theory

Question 1

John Dalton

Answer 1

1803
Discovered the Atomic Theory and proposed that all elements are made of tiny indivisible particles called atoms
Atoms of the same element are identical
Atoms of an element are different to those of any other element
Atoms of different elements combined in simple whole number of ratios to form chemical compounds
In chemical reactions atoms are combined, separated or rearranged but never transformed into an atom of a different element

Question 2

JJ Thompson

Answer 2

1897
Cathode Ray Tube Experiment
Discovered electrons (negatively charge particle)
Plum pudding model
Found that cathode rays have identical properties
He proposed that since atoms are electrically neutral, there must be positive particles but it was not confirmed by him.

Question 3

Ernest Rutherford

Answer 3

1910
Gold Foil Experiment
Shot alpha particles are a thin sheet of gold foil
99% passed through but some were deflected or bounced back
Discovered nucleus and positive protons
Atoms are mostly made of empty space with a small dense positive core, nucleus
He didn’t know about neutrons

Question 4

Niels Bohr

Answer 4

1913
Made the Jimmy Neutron Model
Electrons orbit and exist in several different layers or levels
Electrons can only revolve in certain energy orbits
Electrons jump between levels with energy being added or released
Proposed that electrons exist in specific quantised energy levels

Question 5

James Chadwick

Answer 5

1932
Neutron
Bombarded Beryllium atoms with alpha particles and discovers neutron
No charge or purpose other than to add to the atomic mass
His experiments didn’t account for the missing mass and therefore the neutron appeared.