4. Put forward an atomic theory based on
experiments done with gases.
This theory proposed that:
1. All matter is made up of tiny particles called
atoms.
2. All atoms are indivisible.
They cannot be broken down into simpler
particles.
3. Atoms of the same element have identical
mass and physical properties.
1808
John Dalton
5. 1870’s
William Crookes – Cathode Rays
Radiation coming from the cathode to the
anode.
Radiation caused the paddle wheel to move
6. 1897
J.J. Thomson – Discovery of the Electron
Identified cathode rays as subatomic particles, and measured their charge to
mass ratio e/m.
Identified as electrons.
(George Stoney is credited with the name electron)
7. 1904
J.J. Thomson
Plum pudding model for the atom.
Mass of positively-charged material with electrons (small negative charges)
scattered (embedded) in it.
9. 1909
Rutherford
Some alpha particles were deflected
at large angles
A few alpha particles were
reflected back along their original
path
Most alpha particles passed
straight through undeflected
Particles repelled as they passed
close to a positive mass (nucleus).
Particles collided with a small
dense positive mass (nucleus).
Atom is mainly made up of empty
space.
Note: This observation was not
inconsistent with the ‘plum pudding’
Alpha Particles
Helium nuclei
Particles consisting of 2
protons and 2 neutrons.
10. 1911
Rutherford
Discovery of the protons in the nuclei of various atoms.
Different Elements to Gold
(much lighter)
The alpha particles where breaking up the
nucleus to release positively charged particles
(protons).
