C1.5 - History Of An Atom

Question 1

John Dalton theory

Answer 1

• first theory of an atoms
• dated early 1800s
• believed an atom was a tiny sphere that couldn’t be divided

Question 2

JJ Thompson’s theory

Answer 2

• second theory = dated end of 1800s
• aka ‘plum pudding theory’
• electron was discovered -> negatively charged particles were found
• scientists the sphere had a positive charge and electrons were spread throughout it

Question 3

Ernest Rutherford’s model

Answer 3

• third theory = dated 1908-1913
• proposed the nuclear model
• proposed that electrons orbited the nucleus
• discovered the positively charged nucleus
• Rutherford designed an experiment which was carried out by Geiger and Marsden
• Experiment involved an atom of gold foil and alpha particles

Question 4

Rutherford’s experiment with alpha particles and gold foil

Answer 4

• they fired alpha particles at a piece of atom thick gold foil
• many particles passed straight through but some were deflected
• a mass (nucleus) was discovered in the centre of the gold foil atom
• this prevented some alpha particles from passing

Question 5

Alpha particles

Answer 5

• made up of 2 protons and 2 neutrons = positive charge

- aka the helium atom nucleus

Question 6

Neil’s Bohr theory

Answer 6

• 4th theory= dated 1914

- discovered that electrons orbit the nucleus at a specific distances in certain fixed energy levels (or shells)

Question 7

James Chadwick theory

Answer 7

• dated 1932

- discovered that neutrons were apart of the atomic structure