M8 Topic 2: structure of the atom

Question 1

Who came up with the concept of the atom

Answer 1

John Dalton (1803)

Question 2

What did John Dalton state about the atom

Answer 2

he proposed that each element consist of atoms of a single, unique type, and that these atoms can join to form chemical compounds and that these where indivisible

Question 3

Who was the first person to modify the atom model

Answer 3

J.J.Thomson (1897)

Question 4

How did J.J.Thomson change the atom model (2)

Answer 4

• discovered the electron and its subatomic nature,

- stating the atom consist of a sea of positive charge with electrons distributed throughout it

Question 5

How did J.J.Thomson discover electrons

Answer 5

through the use of cathode ray tubes, he tested the properties of the ray (wave or particle) which was common to all substances

Question 6

what pracs and proof where done to (5)

Answer 6

• Rays pass through electric field: bent (particle)
• Rays pass through Magnetic field : bent (particle)
• Rays pass through metal sheets without interacting (wave)
• Maltese cross (sharp shadows(bno diffraction, block relatively easily) (particle)
• Rays can cause paddle wheel to move (conservation of momentum) (particle)

Question 7

how did J.J.Thomson determine the charge to mass ratio

Answer 7

by measuring the arc of cathode rays when in a magnetic field

Question 8

How was the mass of the electron found

Answer 8

Millikan’s oil drop experiment

Question 9

How was Millikan’s oil drop experiment achieved

Answer 9

1. sprayed small droplets of oil into a electric field
2. looked for droplets that were suspended in the air (force of electric field = weight force)
3. knew density of oil, measure radii to identify mass of the oil
4. Charge determined by equating the two forces ( Eq = mg)

Question 10

What did Millikan’s results uncover about the electron

Answer 10

• discovered all charges where multiple of the same fundamental value = 1.5924 × 10−19 Coulombs which is within 1% of currently accepted value 1.602176487 × 10−19C = charge of a single electron ➞ can calculate mass

Question 11

Who was the second person to modify the atom model

Answer 11

Ernest Rutherford (1909)

Question 12

How did Ernest Rutherford change the atom model

Answer 12

introduced the planetary model where the atom consisted of a dense positively charged nucleus with orbiting electrons with majority of the atom filled with empty space

Question 13

What was the experiment that Rutherford use to determine the planetary structure of the atom

Answer 13

(1909) Geiger and Marsden experiment (under Rutherford’s direction): bombarded gold foil with alpha particles, and expected all alpha particles to go through the gold as the positive charged was to spread out to effect the alpha particle

Question 14

What were the results of the geiger marsden experiment

Answer 14

Discovered a small percentage of alpha particles were deflected, indicating there to be a dense positive charge in the atom hence introducing the nucleus

Question 15

who discovered the proton

Answer 15

Ernest Rutherford in 1918

Question 16

How did Rutherford discover the proton

Answer 16

Used Mass spectrometry to identify the mass of hydrogen = mass of proton

Question 17

Who discovered the neutron

Answer 17

James Chadwick (1930)

Question 18

How did James Chadwick discover the neutron

Answer 18

Used a alpha particle source to hit beryllium which ejected chargeless particles which hit a proton rich paraffin wax releasing protons

Question 19

How did James Chadwick know the particles ejected from the beryllium where particles and not energy (ie gamma rays) (3)

Answer 19

• Determined the velocity of the protons and used the laws of conservation of momentum and energy to determine if it was a gamma ray or a particle
• energy calculated was to small for gamma rays
• Discovering the neutral radiation was made up of particles = in mass of protons