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Chemistry (Tara) > Atomic theory 4 > Flashcards

Atomic theory 4 Flashcards

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1
Q

Who discovered two new elements from impure uranium salt?

A

Marie and Pierre Curie

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2
Q

Which new elements did Marie and Pierre Curie discover?

A

Polonium (Po) and radium (Ra)

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3
Q

What did Marie and Pierre discover Po and Ra from?

A

From impure uranium salt called pitchblende.

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4
Q

What did Marie and Pierre Curie notice?

A

That the radiation carried an electrical charge.

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5
Q

Who noticed that while experimenting with uranium that it was giving off some type of radiation?

A

Henri Becquerel

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6
Q

Henri Becquerel’s timeline

A

1852-1908

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7
Q

What did Henri Becquerel notice while experimenting with uranium?

A

He left some uranium on a photographic plate covered with black paper, the area of the photographic plate near the uranium became darker despite the fact that it had not been exposed to any sunlight = some soft of radiation.

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8
Q

Name an instrument that can detect radioactivity.

A

A Geiger-Muller tube

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9
Q

What does a Geiger-Muller tube do?

A

Detects radioactivity

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10
Q

What are the SI units of radioactivity?

A

Becquerel (Bq)

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11
Q

Define radioactivity

A

Is the spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

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12
Q

What is the charge on alpha particles?

A

Positive particles

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13
Q

Structure of alpha particles.

A

Consist of two protons and two neutrons (hence same as helium nucleus)

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14
Q

Penetrability of alpha particles.

A
  • Not very penetrating
  • Stopped by a sheet of papar / 5cm of air
  • Strongly ionising
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15
Q

Are alpha particles harmless or dangerous?

A

Very dangerous

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16
Q

When are alpha particles very dangerous?

A

If they enter the body through the nose or mouth

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17
Q

What can alpha particles cause if entered through nose or mouth?

A

Mutations in cells

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18
Q

Give an example of alpha emitter and use.

A
  • Americium-241

- Used in smoke detectors

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19
Q

What is the half life of americium-241?

A

Over 400 years

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20
Q

Alpha particles symbolised as

A

He

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21
Q

What is the mass of alpha particles?

A

4 a.m.u

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22
Q

What is done if an alpha particle is lost and you want to find the new element?

A

1 Subtract 2 from the atomic number (bottom number)

  1. Look up new atomic number in periodic table - find new symbol
  2. Subtract 4 from mass number (top number)
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23
Q

Po ⇾ …………….. + He

A

Rn

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24
Q

Charge of beta particles

A

Negatively charged particles

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25
Q

Structure of beta particles

A

Are high-speed electrons

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26
Q

Penetrability of beta particles

A
  • Moderately penetrating
  • Are more penetrating than alpha particles as they are lighter
  • 5mm aluminium metal / 500cm of air
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27
Q

Why are beta particles more penetrating than alpha particles?

A

As they are lighter

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28
Q

Give an example of a beta emitter.

A

Carbon-14

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29
Q

What is carbon-14 used for?

A

To find the age of objects in ‘carbon dating’.

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30
Q

Mass of beta particles.

A

1/1840 a.m.u.

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31
Q

When are beta particles formed?

A

When there are too many neutrons in the nucleus to be stable.

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32
Q

What happens when beta particles form?

A
  • A neutron changes into protons and an electron.

- The electron is ejected from the nucleus. The ejected electron = beta particle

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33
Q

Beta particles symbolised by

A

e

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34
Q

Main use of beta particles

A

To kill cancerous skin cells.

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35
Q

What happens if a beta particle is lost and you want to find the new element?

A
  1. Add 1 to the atomic number (bottom number).
  2. Look up periodic table to find the symbol for the new element.
  3. Leave the mass number the same (top number)
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36
Q

Example of beta particles.

A

Pb ⇾ Bi + e

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37
Q

e

A

0 - top

-1 - bottom

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38
Q

He

A

4 - top

2 - bottom

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39
Q

Gamma rays charge

A

Neutrally charged

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40
Q

Gamma rays structure

A

They are high-energy electro-magnetic radiation.

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41
Q

Name an example of a gamma emitter.

A

Cobalt-60

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42
Q

Gamma rays penetrability

A
  • Extremely penetrating
  • Several cm of lead
  • Very dense metal
43
Q

Does the loss of gamma radiation give rise to a new element?

A

No

44
Q

Why doesn’t gamma radiation give rise to a new element?

A

As it I simply the loss of energy from the nucleus.

45
Q

Main use of gamma radiation.

A

To treat cancer as they kill cancerous cells, but can also cause cancer as they can change the structure of our cells.

46
Q

Alpha (table)

A
  • Positive
  • 2 p + 2n
  • Not very penetrating
  • Am-241
47
Q

Beta (table)

A
  • Negative
  • Electron
  • Moderately penetrating
  • C-14
48
Q

Gamma (table)

A
  • Neutral
  • Electromagnetic radiation
  • Extremely penetrating
  • Co-60
49
Q

Difference between nuclear reactions and chemical reactions.

A

A nuclear reaction involves a change in the nucleus of an atom and a new element is usually formed as a result.
A chemical reaction involves electrons being shared or transferred from one atom to another - the nucleus of the atom remains the same.

50
Q

Define chemical reaction

A

A chemical reaction involves electrons being shared or transferred from one atom to another - the nucleus of the atom remains the same.

51
Q

Define half-life

A

This is the time taken / for half the nuclei / in given sized sample to decay.

52
Q

Is the emission of radiation affected by external conditions like chemical reactions, pressure and temperature?

A

No

53
Q

What is the one factor that appears to govern the overall rate of decay?

A

The number of nuclei left undecayed.

54
Q

What is the one factor that appears to govern the overall rate of decay?

A

The number of nuclei left undecayed.

55
Q

What do experiments show?

A

That the time taken for half of the atoms in a sample of a radioisotopes to decay is constant for that particular isotope.

56
Q

What is the half life of radon-222?

A

3.2 days

57
Q

What is the half life of iodine 131?

A

8 days

58
Q

What is the half life of uranium-238?

A

4.5 billion years

59
Q

Define radioisotopes

A

This is an isotope of an element that undergoes radioactive decay.

60
Q

Uses of radioisotopes

A
  1. Nuclear power
  2. Cancer treatment
  3. Sterilisation
  4. Archaeological uses
61
Q

What is meant by using radioisotopes for nuclear power?

A

Heat generated in nuclear power stations by nuclear reactions is used to produce electricity.

62
Q

What is meant by using radioisotopes in cancer treatment?

A

Gamma rays of cobalt-60 are used to kill cancerous cells inside the body. Beta rays are used to treat skin cancers, as they are less penetrating.

63
Q

What is meant by using radioisotopes in sterilisation?

A

Radiation is used to sterilise medical equipment. It is also used to kill bacteria to give food a longer shelf life.

64
Q

What is meant by using radioisotopes for archaeological uses? (just understand)

A

The carbon-14 isotope is radioactive and is present as a very small amount of CO₂ in the air that is used by plants in photosynthesis and ends up in animals when they eat plants. The ratio of carbon-12 to carbon-14 remains constant when the organism is alive.

65
Q

How can the time of death of the organism can be calculated.

A

By measuring the ratio of carbon-12 to carbon-14 and knowing the half-life of carbon-14.

66
Q

What is nuclear fission?

A

A nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the release of energy.

67
Q

What is nuclear fusion?

A

Is the joining of two smaller nuclei to form a larger one. Energy is given out.

68
Q

Define radioactivity (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

69
Q

What change takes place in the structure of the nucleus of an atom when beta decay occurs? (L.C)

A

A neutron changes into a proton.

70
Q

Write a balanced equation for the beta decay of a carbon-14 nucleus. (L.C)

A

n

71
Q

A piece of fossilised yew, from a tree that was alive about 6000 years ago, was excavated from Boora Bog, Co. Offaly. When a tiny fragment of it was analysed, it was found to contain 1.5 x 10(12) carbon-14 atoms. Explain why the fragment of yew must have contained 3.0 x 10(12) carbon-14 atoms 5730 years before the analysis. What mass of carbon-14 did the fragment contain 5730 years before the analysis? (L.C)

A

nn

72
Q

Explain why the fragment of yew must have contained 3.0 x 10(12) carbon-14 atoms 5730 years before the analysis. What mass of carbon-14 did the fragment contain 5730 years before the analysis? (L.C)

A

n

73
Q

What are isotopes? (L.C)

A

Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

74
Q

What is a radioisotope? (L.C)

A

n

75
Q

Define the half-life of a radioisotope. (L.C)

A

nn

76
Q

Complete the following nuclear equation to show the alpha decay of radium-226. Ra ⇾ ___ + ___ (L.C)

A

n

77
Q

Radium-223 undergoes alpha decay and is also used in radiotherapy. Starting with a sample containing 1.0 x 10(-4) moles of radium-223, how many of these atoms remain when 87.5% of the sample has decayed? (L.C)

A

n

78
Q

What change takes place in the nucleus of an atom when beta decay occur? (L.C)

A

n

79
Q

Write a balanced nuclear equation for the beta-decay of the Fr nucleus (223 - top, 87 - bottom) (L.C)

A

n

80
Q

Define radioactivity (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

81
Q

Give two differences between chemical reactions and nuclear reactions. (L.C)

A

nn

82
Q

Give two properties of beta-particles. (L.C)

A
  • Negative
  • Moderately ionising
  • Less penetrating power than α
83
Q

A certain mass of caesium-137 leaked on a particular day. What fraction of this mass remained as caesium-137 after 90 days? (L.C)

A

n

84
Q

What are isotopes? (L.C)

A

Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

85
Q

Define radioactivity. (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

86
Q

Define radioisotope. (L.C)

A

n

87
Q

Carbon-14 decays by the beta particle emission. Write a balanced equation to describe beta-decay of the carbon-14 nucleus. (L.C)

A

n

88
Q

Explain why the carbon-12 to carbon-14 isotope ratio in the shoe leather changed over 5500 years since the shoe was made. (L.C)

A

nn

89
Q

Define radioactivity (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

90
Q

Define the half-life of a radioactive isotope. (L.C)

A

n

91
Q

Alpha particles are hazardous to human health. State one risk associated with exposure to alpha radiation. (L.C)

A

n

92
Q

Explain why the occupants of a house fitted with smoke detectors containing americium-241 are not at risk from alpha radiation emitted by these devices. (L.C)

A

n

93
Q

Householders are advised to replace the batteries in smoke detectors regularly. Explain whether or not the americium-241 needs to be replaced regularly also. (L.C)

A

n

94
Q

What change occurs in the nucleus of an atom when it undergoes beta emission. (L.C)

A
  • Neutron changes to proton
95
Q

Give two properties of alpha particles. (L.C)

A
  • Positive charge
  • Poor penetration
  • Stopped by a few sheets of paper
96
Q

Give two differences between a nuclear reaction and a chemical reaction. (L.C)

A
  • Involves nucleus of atoms not electron cloud

- Involves new elements being generated

97
Q

Define radioactivity. (L.C)

A

The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.

98
Q

State three properties of beta particles. (L.C)

A
  • Negative
  • Moderately ionising
  • Less penetrating power than α
99
Q

Explain how the carbon-14 isotope allows certain archaeological discoveries to be dated. (L.C)

A
  • In living things, the ratio of carbon-12 to carbon-14 is constant.
  • Decrease in carbon-14 related to time passed since death.
100
Q

List the following three types of radiation in order of increasing penetrating power. Alpha, beta, gamma (L.C)

A

Alpha, beta, gamma

101
Q

Explain how Rutherford interpreted the results of his experiment to conclude that the atom has a nucleus. (L.C)

A
  • Mass concentrated / atoms mainly made up of empty space.
102
Q

What are alpha particles? (L.C)

A

Two protons and two neutrons

103
Q

Describe an experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. (L.C)

A
  • Bombarded gold foil with alpha particles
  • Used zinc sulfide detector
  • Most passed straight through
  • Some were deflected at large angles
  • Some were reflected

Chemistry (Tara) (50 decks)

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