Chapter 2 - Atoms Flashcards
Who said matter was made up of small particles
Greek philosophers
Democritus was one
How was the Electron discovered
Passed electric currents (cathode rays) through a glass tube (vacuum tube) containing air at low pressure
• Crookes Rays
• Radiation was coming from metal plate (cathode)
• Shadow of Maltese cross
• Cause glass to fluoresce
Crookes Paddle Wheel
Investigate property of cathode rays
Vanes always turned away from cathode
J.J Thompson
- Proved cathode rays consisted of negatively charged particles
- Cathode rays attracted to positive beam of light
- Caused fluorescent screen to glow
• High voltage is dragging electrons out of the atoms of the cathode
J.J Thompson’s Second Experiment
MEASURED CHARGE/MASS OF ELECTRON (E/M)
• Placed a large electromagnet outside the glass tube
• Adjusted the strength of the magnetic field
• Brought a beam of electrons down to its original position
Robert Millikan
MEASURED CHARGE OF ELECTRON
• Oil Drop Experiment
• X- rays to ionise air between plates
• Negatively charged oil droplets between two charged plates
• Adjusted charge on plates until an oil droplet was stationary
Thompson’s Plum Pudding Model
An atom is a sphere of positive charge
Electrons are embedded in the sphere at random
Ernest Rutherford
DISCOVERED NUCLEUS (+)
• Bombarded gold foil with alpha particles (+)
• Some went through. Some were deflected.
• Phosphorescent screen made of zinc sulfide to detect alpha particles
• Most of the atom is empty space
Discovery of Proton (+)
- Bombarded other things
- Alpha particles broke nuclei of light atoms to release protons
- In heavier atoms, large positive nuclear charge repelled alpha particles
- Atoms consist of a small dense positive core (nucleus)
- Protons were located in nucleus
James Chadwick
DISCOVERED NEUTRON
• Bombarded beryllium with alpha particles
• They knicker neutrons our of nuclei of beryllium atoms
• Paraffin wax to detect them
• Neutrons knocked protons out of paraffin wax
• Radiation with particles with no charge came from beryllium (neutron)
Power of Neutrons
They brought about the splitting of atoms of uranium to release nuclear energy
Who proposed a theory of atoms in 1808
John Dalton