Topic 1 Key Concepts in Chemistry - History of the Atom

Question 1

What are the three ideas in John Dalton’s theory about the atom?

Answer 1

• Atoms can not be created, divided or destroyed.
• Atoms of the same element are exactly the same and atoms of different elements are different.
• Atoms join with other atoms to make new substances.

Question 2

What discovery caused the original Dalton model of an atom to change?

Answer 2

The discovery of subatomic particles.

Question 3

How did JJ Thomson discover the electron?

Answer 3

Thomson experimented with a cathode ray tube.

The beam moved towards the positively charged plate so he knew that the particles must have a negative charge.

Question 4

Describe the atomic model proposed by JJ Thomson

Answer 4

Plum pudding model.

Negatively charge electrons scattered through a positively charged material.

Question 5

What did Ernest Rutherford discover from his gold foil experiment?

Answer 5

He shot a beam of positively charged particles at a sheet of gold foil.

• Most of the particles passed straight through suggesting that atoms were mostly empty space
• A few particles were deflected and a few bounced directly back showing that there must be a tiny, dense and positively-charged nucleus

Question 6

Describe Rutherford’s new model of the atom

Answer 6

• Mass is concentrated in the central nucleus.
• Mostly empty space.
• Electrons travel in random paths around the nucleus.