History of the atom

Question 1

Explain the Billiard Ball model ?

Answer 1

-John Dalton
-1804
-Atom are solid spheres which cannot be split up
-All atoms of an element are the same and therefor isotopes do not exist

Question 2

Explain the Plum Pudding model ?

Answer 2

-1897
-J.J. Thompson
-He conducted an experiment with a cathode-ray tube which identified the electron as a negatively charged subatomic particle .
-Majority is a positive mass
-Negatively charged articles are randomly placed

Question 3

Explain the nuclear model of the atom ?

Answer 3

-Ernst Rutherford
-1909
-Discovered the positive nucleus.
-Shot a beam of positively charged particles (alpha particle) at a thin sheet of gold .(He expected the particles to pass straight through the gold due to the positive charge being thought to be evenly spread )
-While the majority were scattered ,some were reflected back.
-This led them to believe the majority of the nucleus was positive and that the atom was mainly made up of empty space.

Question 4

Who discovered electrons and give details ?

Answer 4

-1913
-Niel Bohr
-Proposed that electrons orbit the nucleus in fixed shells
-Electrons moved in fixed positions and distances from the nucleus .
-When an electron moves between shells ,electromagnetic radiation is emitted (moving closer to the nucleus ) or taken in (moving further from the nucleus )
-Because the energy of shells is fixed ,the radiation will have a fixed frequency
-The frequency of radiation emitted and absorbed by atoms were already known from experiments ,Bohr’s model fitted these observations .

Question 5

Describe the discovery of neutrons ?

Answer 5

-James Chadwick
-1932
-Found evidence for the existence of particles in the nucleus with mass
-Led to Modern day models .