Atomic Theory: Early
Early Theorists
The Alchemists
• Explored the nature of matter (usually very wrong)
• Egypt, India, Persia, Europe, China and Japan
• Searched for the “elixir of life” and the “philosopher’s stone”
• Developed lab procedures and equipment
Dalton: 1803
• His atomic theory:
– All matter is made up of tiny particles called atoms
– Atoms of one element cannot be converted into atoms of any other element
– All atoms of one element have the same properties and these are different from atoms of
other elements
– Atoms combine in specific proportions
– Chemical change is the union or separation of atoms
– Atoms cannot be created nor destroyed
Most points correct except
a)
b)
The Discharge Tube (Crooks’
tube/Cathode Ray tube)
•
•
•
Instrument being used to study electricity
Glass tube sealed at both end with metal plates
Different gases glowed different colours
•
No gas but still fluorescent glow around anode end
•
Crooke had found the electron but didn’t know it at the time, called the rays “cathode rays”
• When he removed gas there was still fluorescent
glow around anode end
• Crooke had found the electron but didn’t know it
at the time, called the rays “cathode rays”
JJ Thomson ~1897
• Discovered and proved glow around anode was made up of electrons
• Subjected the cathode rays to magnetic and electric fields
• Found rays were deflected
• Measured the angle of deflection and found the charge to mass ratio of an
electron
• Found that ALL gases had the SAME charge : mass ratio
• Concluded electrons were part of all matter
• Thomson’s model was a positive sphere with electrons
Rutherford~1912
• Bombarded thin sheet of gold foil with alpha
particles (positive charge)
• Most passed through and hit a moveable zinc
sulfide detector and gave off a flash of light
• Most alpha particles passed right through,
atoms mostly empty space
• Some alpha deflected at large angles
• ~1 in 8000 bounced in the opposite direction
and rate of deflection was constant
• Rutherford’s atomic model was an atom with
a very small, dense, positively charged region
at the centre
• Most mass was in the nucleus
• Electrons orbit the nucleus
Homework
• Supplement your notes!!
• Merrill: p.78-82
• Nelson: p.11-13 up to Chadwick
p.6 #1-6