Chemistry: Lesson 7 & 8 (History and Parts of the Atom & Bohr-Rutherford Diagrams))

parts of the atom

 

Electron	Negatively charged; orbits nucleus
Proton	Positively charged; inside nucleus
Neutron	No charge (neutral); inside nucleus

John Dalton: Billiard Ball Model

• Dalton proposed that atoms were tiny indivisible spheres, like billiard balls (can’t be broken down further)

• Proven incorrect

Heinrich Geissler: Gas Discharge Tube

• Gas discharge tubes are hollow glass tubes with electrodes (metal) at each end, which glow when electricity is run between the electrodes

• Geissler improved the original gas discharge tube by including a vacuum pump (to remove gas inside the tube), which caused the tube to glow green

J.J. Thomson: The Plum Pudding Model

• Experimented with vacuum tubes  

• Concluded that a tiny particle was passing through the tube and this was what made the tube glow green

• It was concluded that the particles must be negative, as they would be repelled from the negative side of the power source, called electrons.

Ernest Rutherford: The Gold Foil Experiment

• Radium was placed inside a lead block so that the positively charged particles could only escape in one direction

• The particle beam was aimed at a piece of gold foil that was only a few atoms thick

• The results were mostly as expected - 9999 out of every 10 000 particles when straight through the foil, however, the particles that didn’t go straight through were deflected at many different angles.

James Chadwick: Discovery of the Neutron

• Chadwick noticed the hydrogen had one proton, and helium had two, yet helium had a mass four times that of hydrogen. But why? 

• He identified an uncharged particle in the nucleus with a mass almost identical to a proton, called the neutron

Bohr-Rutherford Model

• Niels Bohr and Ernest Rutherford proposed that electrons can only circle the nucleus at specific distances he called energy levels

• Believed atoms are like tiny solar systems

Subatomic particles

 

Subatomic Particle	Location	Charge	Size/Mass
Proton	Inside Nucleus	Positive (+)	Large/Heavy 1.0073 amu
Electron	Orbits Nucleus	Negative (-)	Small/Light 0.00055 amu
Neutron	Inside Nucleus	Neutral (0)	Large/Heavy 1.0087  amu

how to find the neutrons?

atomic number = protons = electrons

neutrons = atomic mass - atomic number/protons/electrons