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Physics > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

Democritus’ theory of atom

A
  • 5th Century BC
  • all matter was made up of identical lumps called ‘atamos’
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2
Q

Dalton theory of atom

A
  • 1804
  • agreed with Democritus that matter was made up of tiny spheres
  • thought each element was made up of different type of ‘atom’
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3
Q

JJ Thomson theory of atom

A
  • 1897
  • discovered electrons that could be removed from atoms
  • plum pudding model - atom is ball of positive charge with negative electrons embedded throughout
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4
Q

Alpha scattering experiment

A
  • Rutherford - 1909
  • fired beam of alpha particles at thing gold foil
  • most particles went straight through sheet, some deflected in random directions, few deflected back the way they came
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5
Q

Conclusions of Alpha scattering experiment

A
  • nuclear model of atom
  • most mass is concentrated in centre in nucleus
  • nucleus is positive - it repelled positive alpha particles
  • mostly empty space as most when straight through
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6
Q

Niels Bohr atom theory

A

Elections orbiting nucleus do so at certain distances on shells/energy levels

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7
Q

James Chadwick atom theory

A
  • 1932
  • discovered neutron
  • explained imbalance between between atomic and mass numbers
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8
Q

Current model of atom

A
  • small nucleus concentrates most mass in centre, contains positive protons and neutral neutrons
  • mostly empty space
  • electrons orbit nucleus on shells/energy levels
  • equal number of protons and electrons - no overall charge
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9
Q

What happens if electrons absorb EM radiation

A

They move to higher energy levels

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10
Q

What happens when electrons release EM radiation

A

They move to lower energy levels

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11
Q

Isotopes

A

Atoms with the same number of protons but different number of neutrons

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12
Q

Radioactive decay

A

Unstable isotopes decaying into other elements to become more stable, giving out radiation

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13
Q

Ionising radiation

A

Radiation that knocks electrons off atoms, creating positive ions

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14
Q

Ionising power

A

How easily a radioactive source can knock electrons off atoms

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15
Q

Types of radiation

A
  • alpha
  • beta
  • gamma
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16
Q

What is an alpha particle

A
  • 2 protons and 2 neutrons
  • like a helium nucleus
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17
Q

Alpha particles penetration

A

Low

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18
Q

Alpha particles range

A

cm in air

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19
Q

Alpha particles ionising power

A

High

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20
Q

What stops alpha particles

A
  • paper
  • skin
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21
Q

Why are alpha particles strongly ionising

A

They are large

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22
Q

What is a beta particle

A
  • fast moving electron released from nucleus from neutron turns into a proton
  • hardly any mass
  • charge of -1
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23
Q

Beta particle penetration

A

Moderate

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24
Q

Beta particle range

A

Metres in air

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25
Q

Beta particle ionising power

A

Moderate

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26
Q

What stops beta particles

A

Around 5mm of aluminum

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27
Q

Uses of alpha radiation

A

Smoke detectors - ionises air particles causing current to flow, if smoke it binds to air particles, current stops, alarm sounds

28
Q

Use of beta radiation

A

Beta emitters - test thickness of sheets of metal as particles are not immediately absorbed by material

29
Q

What is gamma radiation

A

Rays of electromagnetic radiation released by nucleus

30
Q

Gamma radiation penetration

A

High

31
Q

Gamma radiation range

A

Km in air

32
Q

Gamma radiation ionising power

A

Low

33
Q

Why is gamma radiation lowly ionising

A
  • waves tend to pass through rather than collide with atoms
  • eventually hit something and do damage
34
Q

What stops gamma radiation

A
  • sheets of lead
  • metres of concrete
35
Q

Form of nuclear equations

A
  • atom before decay —> atom after decay + radiation emitted
  • total mass and atomic numbers must be equal on both sides
36
Q

Effect of alpha decay on nucleus

A
  • charge decreases by 2
  • mass decreases by 4
37
Q

Effect of beta decay on nucleus

A

Charge increases by 1 (gained proton)

38
Q

Effect of gamma rays on nucleus

A

No effect

39
Q

What device measures radiation

A

Geiger-Muller tube and counter

40
Q

What does Geiger-Muller tube and counter measure

A

Count-rate

41
Q

Count-rate

A

Number of radiation counts reaching Geiger-Muller tube and counter per second

42
Q

Effect of radioactive decay being random

A

You can’t predict which nucleus in a sample will decay next and when

43
Q

Half-life

A
  • time taken for the number of radioactive nuclei in an isotope to halve
  • time taken for the activity to fall to half of its initial value
44
Q

Use of half-life

A
  • can make predictions about radioactive sources
  • can find source’s activity
45
Q

Activity

A

Rate at such radioactive source decays

46
Q

What is activity measured in

A

Becquerels (Bq)

47
Q

What is a becquerel

A

Om1 Bq is 1 decay per second

48
Q

What happens to activity and radioactivity of a source over time

A

Decreases as older sources emit less radiation

49
Q

When does activity reach 0

A

Never

50
Q

Why is activity higher than count-rate

A

not all the radiation emitted by the sample is detected because the radiation spreads out

51
Q

Axis on a half-life graph

A
  • X - activity (Bq)
  • Y - time (s)
52
Q

Risk of using radiation

A

Ionising radiation can enter living cells and ionise their atoms, damaging (which can cause cancer) or killing them

53
Q

Irradiation

A

Exposure to radiation

54
Q

How to reduce effects of irradiation

A
  • keeping sources in lead-lined boxes
  • standing behind barriers when using sources
  • keeping source in different room and handling with remote controlled arms
55
Q

Contamination

A

Radioactive particles getting onto objects

56
Q

Dangers of contamination

A
  • contaminating atoms on skin may decay, releasing radiation and causing you harm
  • radioactive particles could get inside your body
57
Q

How to prevent contamination

A
  • using gloves and tongs when handling sources to avoid particles getting stuck under nails
  • wearing protective suits to stop breathing in particles
58
Q

Most dangerous sources of radiation outside body

A
  • beta
  • gamma
59
Q

Why are beta and gamma radiation most dangerous outside the body

A

They can penetrate the body and get to delicate organs

60
Q

Why is alpha radiation less dangerous

A

It can’t penetrate skin and is easily blocked by a small air gap

61
Q

Most dangerous radiation source inside body

A

Alpha

62
Q

Why is alpha most dangerous radiation source in body

A
  • highly ionising - can ionise and damage/kill cells
  • do all their damage in localised area
63
Q

Largest concern when working with alpha sources

A

Contamination - alpha radiation does damage inside of body

64
Q

Why are beta sources less damaging in body

A

Radiation is absorbed over a wider area and some passes out of the body altogether

65
Q

Least dangerous radiation source inside body

A

Gamma

66
Q

Why is gamma least dangerous inside body

A
  • mostly passes straight out
  • lowest ionising power

Physics (4 decks)

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