History of the atom

Question 1

List the significant models proposed for atoms.

Answer 1

The Plum Pudding Model
The Nuclear Model
Bohr’s Model

Question 2

Who was JJ Thomson and what did he discover?

Answer 2

. JJ Thomson was a scientist and was responsible for discovering the electron.
. He also believed the atom is a ball of positive charge with negative electrons embedded in it.

Question 3

Who were Geiger and Marsden?

Answer 3

• Fired alpha particles at thin gold foil
• Expected the particles to pass straight through the foil.
• Some particles were repelled back towards the source.

Question 4

What did Ernest Rutherford believe about the atom after ‘The gold Foil Experiment’?

Answer 4

• Most of the atom is empty space
• Most of the mass of the atom is in the centre of the atom (nucleus).
• Positive charge is concentrated at the nucleus.
• Nucleus is small dense and positively charged.

Question 5

What did Niels Bohr think of about the structure of the atom?

Answer 5

• Electrons orbit the nucleus at set distances.
• Electron shells have a fixed energy (energy levels)
• When electrons move from high to lower energy level, they release a set amount of energy.

Question 6

Name the main scientists related to the development of the atomic theory, in order.

Answer 6

John Dalton
JJ Thomson
Ernest Rutherford
Niels Bohr

Question 7

Justify why the model of the atom has changed over time.

Answer 7

• New discoveries
• Technological advances
• inherent self- correcting nature of scientists

Question 8

Why did chemists not accept Newlands’ Law of Octaves?

Answer 8

Chemists did not accept Newlands’ ideas because his law of octaves was limited in scope, grouped dissimilar elements together, failed for heavier elements, and didn’t accommodate missing elements