Atomic Theory

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

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.

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

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

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.