The atom - Ch2

Question 1

DALTON’S ATOMIC THEORY

Answer 1

All matter is made up of small particles and all atoms are indivisible. Atoms of different elements vary in mass.

Question 2

LAW OF CONSERVATION OF MASS

Answer 2

Matter is neither created nor destroyed in the course of a chemical reaction.

Question 3

CROOKES

Answer 3

Fired cathode rays in a vacuum tube:
- Obs: shadow of maltese cross + turned paddle wheel
- Cathode rays travel in straight lines

Question 4

THOMSON

Answer 4

• Fired narrow beam of cathode rays between charged parallel plates
• Showed that cathode rays are negatively charged
• Measured the ratio of charge : mass of an electron (e/m)
• Plum pudding model

Question 5

STONEY

Answer 5

Proposed the name “electrons”

Question 6

MILIKAN

Answer 6

• Oil drop experiment
• Measured the charge of the electron

Question 7

RUTHERFORD

Answer 7

Discovered nucleus of an atom and the existence of protons in the nucleus.

Question 8

RUTHERFORD’S EXPERIMENT

Answer 8

Fired alpha particles at gold foil.

Question 9

RUTHERFORD’S EXPERIMENT EXPECTATIONS

Answer 9

S + S
- Some alpha particles would pass straight through
- Some alpha particles would take slight deflections

Question 10

RUTHERFORD’S EXPERIMENT RESULTS + CONCLUSIONS

Answer 10

• Most A.P passed straight through gold foil: atom mostly consists of empty space
• Some A.P were deflected at large angles: came near positive body and got repelled
• Very very few A.P were reflected back along their own paths: hit a small dense body

Question 11

ALPHA PARTICLES

Answer 11

• Hellium nuclei
• Positively charged
• Little penetrating ability
• 2p + 2n

Question 12

CHADWICK

Answer 12

• Bombarded sample of beryllium with alpha particles
• Discovered the neutron

Question 13

CATHODE RAYS

Answer 13

• Streams of negatively charged particles (electrons)
• Travel in straight lines from cathode to anode
• Deflected by electric and magnetic fields
• Have enough energy to move small objects