3.1: Early History of Atomic Theories

Question 1

300 B.C Greeks

Answer 1

atomos - matter made up of indivisible particles

Question 2

John Dalton

Answer 2

• matter consists of atoms
• atoms cant be created, destroyed, or divided
• atoms of diff types combine in specific ratios to form compunds

Question 3

J.J Thomson: Raison Bun Model

Answer 3

experimented w gas discharge tubes and cathode rays resulted in determination of charge-to-mass ratio of cathode ray (aka electron)
proposed model of atom - positive sphere w embedded negative electrons

Question 4

1911 - Ernest Rutherford: Gold Foil Experiment

Answer 4

• radium atoms emit positive alpha particle (He nucleus) radiation
• tested thomson’s model by firing alpha particles at thin piece of gold
  alpha particles seen to either pass through or deflect at angles (falsifies thomson’s model)

Question 5

Nuclear Model

Answer 5

• rutherford proposed model of atom - atom consists of empty space occupied by electrons called nucleus help together by nuclear force

Question 6

1914 Rutherford and Thomson

Answer 6

• rutherford analyzed alpha particle deflections to estimate number of positive charges on nucleus of atom of metal foil
• nuclear mass based on number of protons was less than actual mass
• missing mass must be due to other neutral particles

Question 7

1952 - James Chadwick

Answer 7

discovered neutron

Question 8

Nuclear Model Summary

Answer 8

• atom composed of equal number of protons and electrons
• atomic centre called nucleus and contains protons and neutrons densely packed
• electrons orbit nucleus