MODULE 8 IQ 2

Question 1

atomic theory

Answer 1

• all matter is made up of atoms which are indestructible and indivisible
• all atoms in an element are identical in mass and properties
• compounds are formed by combination of 2 or more different kinds of atoms

Question 2

cathode ray experiments aim and the different types

Answer 2

• determine whether cathode rays were waves or particles
• fluorescent screen, maltese cross, paddle wheel, magnetic field, electric field

Question 3

flourescent screen cathode ray experiment

Answer 3

placing fluorescent inside cathode ray tube
- fluorescence tracing path cathode rays –> shows they have energy
- no determination whether they were waves or particles

Question 4

maltese cross cathode ray experiment

Answer 4

• sharp shadows created around cross
• no diffraction or fuzzy outline (expected of waves)
• cathode rays travel in straight line

Question 5

paddle wheel cathode ray experiment

Answer 5

• when potential difference is turned on, paddle wheel rotates and rolls away from cathode and towards anodes
  cathode rays have:
• momentum and thus mass
• carried and transferred energy and momentum to paddle wheel
• particles

Question 6

magnetic field cathode ray experiment

Answer 6

only negative charges experience force in external magnetic field –> cathode rays are negatively charged particles

Question 7

electric field cathode ray experiment

Answer 7

cathode ray deflects towards positively charged plate –> negatively charged

Question 8

JJ Thomson’s charge-to-mass ratio experiment method

Answer 8

• double collimator tubes: accelerated electrons, focused electrons into narrow beam
• electrons pass through anode with slit –> constant velocity
• 2 parallel electric plates inside vacuum tube connected to electric source –> uniform electric field down the page

Question 9

JJ Thomson’s charge-to-mass ratio experiment observations

Answer 9

• only electric field turned on –> cathode ray deflected towards positive plate following parabolic path

Question 10

conclusions of JJ Thomson’s experiment

Answer 10

q/m ratio of cathode ray was x1837 than known q/m ratio of hydrogen ion
- cathode rays are fundamental particles –> thus called these particles electrons

Question 11

thomson’s plum pudding model

Answer 11

positive atom embedded with smaller negative electrons
- unable to explain what the positive mass within the atom was at the time –> neutron and proton hadn’t been discovered yet

Question 12

Millikan’s Oil Drop experiment method

Answer 12

atomiser to disperse oil droplets into chamber, encountering strong electric field.
- X-rays were employed to ionise gas molecules leading to generation of free electrons that subsequently adhered to oil droplets –> negative charge
- positive terminal was above, upward-directed electric force on oil droplets
- droplets were subjected to downward gravitational force, upward buoyant force, drag force
- adjust voltage

Question 13

geiger-marsden gold foil experiment

Answer 13

helium nuclei were shot out of radioactive source against thin gold foil
- vacuum placed around experiment –> alpha particles would only be deflected due to their interactions with gold atoms
- alpha particles would only deflect due to 1 gold atom

Question 14

geiger-marsden gold foil experiment predictions

Answer 14

alpha particles shot into a positive sphere with embedded negative charges would only cause tiny deflections due to attraction and repulsion

Question 15

geiger-marsden gold foil experiment results

Answer 15

majority of alpha particles went through gold foil with little to no deflection
- 1/8000 alpha particles would be deflected at angles larger than 90 degress

Question 16

rutherford’s explanation of geiger-marsden gold foil experiment results

Answer 16

coulomb’s law: F=kq(1)q(2)/d^2
- positive charge in atom was in a smaller region than rest of electrons –> nucleus

Question 17

rutherford’s planetary atomic model

Answer 17

dense, positively charged nucleus in middle of atom
- electrons were orbiting nucleus due to attractive force between their negative charge and the positive charge stemming from the nucleus
- did not know stationary states, protons and neutrons

Question 18

problems with rutherford’s planetary atomic model

Answer 18

• electrons should be accelerating centripetally and emit EMR –> lose energy in their orbit, ‘fall’ into nucleus
• atoms should theoretically produce continuous spectra, contradicting established hydrogen emission lines
• did not account for positively charged nucleus

Question 19

chadwick’s discovery of the neutron (1932)

Answer 19

• LOCOE should remain true –> radiation being emitted from beryllium sheet was from neutral particles (neutrons)
• LOCOM and KE of protons and neutrons –> mass of neutron was slightly larger than proton