History of the Atom

Question 1

What was the Alpha Scattering Experiment?

Answer 1

Scientists fired alpha particles (which are positively charged) at a sheet of gold foil and observed how they scattered

Question 2

What did the Alpha Scattering Experiment show scientists?

Answer 2

• Most of the alpha particles passed straight through the gold foil - told scientists that atoms were mainly empty space, disproving the plum pudding model
• Some were deflected - told scientists that the centre of the atom must have a positive charge (as positive particle would be repelled)
• Some bounced back off - told scientists that the centre must contain lots of mass
• From results, scientists replaced the plum pudding model with the nuclear model

Question 3

Plum Pudding Model:

Answer 3

• JJ Thompson
• atom is a ball of positive charge with negative electrons embedded in it

Question 4

Neil Bohr

Answer 4

• suggested electrons orbit the nucleus at specific distances (shells)

Question 5

James Chadwick

Answer 5

• proved existence of neutrons within a nucleus

Question 6

How were atoms first described in 500 BC?

Answer 6

• Democritus first had the atom theory
• Small spheres
• Separated from each other by empty space
• The smallest possible unit of matter