ATOM TIMELINE

JOHN DALTON 1808-1827

• Suggested that forces of repulsion is thought to cause pressure only between atoms of same kind and atoms in mixture were different in weight and complexity.
• If two elements can combine then combinations will occur in set sequence.

J.J. THOMSON 1897

• Investigating cathode Rays when suggesting the Rays are streams of particles smaller than atoms
• Called them "corpuscles" and they make up all matter in atoms
• His suggestion of cathode Rays were right, atoms are made of electrons

PLUM PUDDING ATOMIC MODEL 1904

• Suggested by J.J. Thomson
• Negatively charged electrons mixed with smeared out positive charges

ROBERT MILLIKAN 1910

• Accurate determination of charge carried by electron, using "falling-drop" method
• Proved this quantity was a constant for all electrons atomic structure of electricity

BOHR PLANETARY MODEL 1915

• Suggested by Niels Bohr
• Neutrons and protons occupy a nucleus and electrons orbit the nucleus

JAMES CHADWICK

• Proved the existence of neutrons

HENRY MOSELEY

• Developed the periodic table

NIELS BOHR

• Energy is only transferred in well defined quantities
• Electrons move around the nucleus