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Physics > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

Define atom

A

The smallest part of an element that can exist

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2
Q

Define element

A

A substance made of only one type of atom

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3
Q

Define compound

A

A substance made of two or more different atoms chemically bonded together in fixed proportions

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4
Q

Define molecule

A

A substance made of more than one atom chemically bonded together

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5
Q

Define mixture

A

Two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged

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6
Q

Give an approximation for the radius of an atom

A

1x10(-10) metres

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7
Q

What are the three subatomic particles?

A

Proton, neutron, electron

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8
Q

Where is most of the mass of an atom concentrated?

A

In the nucleus

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9
Q

Approximately what proportion of the total radius of an atom is the radius of the nucleus?

A

1/10,000

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10
Q

Describe the arrangements of protons, neutrons, and electrons in an atom

A

Protons and neutrons are found in the atom’s nucleus
The electrons are found in shells at certain distances from the nucleus

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11
Q

What type of charge does the nucleus of an atom have and why?

A

Positive charge
The nucleus contains protons and neutrons
Protons have a positive charge
Neutrons have no charge

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12
Q

Give two ways that an atom’s electron arrangement can be changed

A

Absorbing electromagnetic radiation
Emitting electromagnetic radiaion

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13
Q

Explain how an atom’s electron arrangement changes when it absorbs EM radiation

A

Electrons move further away from the nucleus
They move to a higher energy level

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14
Q

Explain how an atom’s electron arrangement changes when it emits EM radiation

A

Electrons move closer to the nucleus
They move to a lower energy level

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15
Q

How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

A

The number of protons is equal to the number of electrons
Protons and electrons have equal and opposite charges, so charge cancels

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16
Q

What do all forms of the same element have in common?

A

They all have the same number of protons

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17
Q

What is the name given to the number of protons in an atom?

A

Atomic number

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18
Q

What is an atom’s mass number?

A

The total number of protons and neutrons in the atom

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19
Q

What is an isotope?

A

An atom of an element that has a different number of neutrons, but the same number of protons

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20
Q

How do atoms turn into positive ions?

A

They lose one or more of their outer electrons
Electrons are negatively charged, so the resultant charge of the atom is positive

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21
Q

What may lead to a scientific model being changed or replaced?

A

The discovery of new experimental evidence which doesn’t agree with the existing theory

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22
Q

How did the plum pudding model describe the atom?

A

A ball of positive charge, with negatively charged electrons embedded in it

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23
Q

Prior to the discovery of the electron, what was believed about the atom?

A

The atom was believed to be indivisible

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24
Q

Which experiment led to the plum pudding model being discarded?

A

Rutherford’s alpha scattering experiment

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25
Q

What is the name given to the currently accepted model of the atom?

A

The Bohr nuclear model

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26
Q

State the conclusions of the alpha scattering experiment?

A

Most of the mass of the atom is concentrated at the centre of the nucleus
The nucleus is positively charged

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27
Q

What reinforces a scientific theory?

A

When experimental results agree with the hypothesised theoretical calculations and theories

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28
Q

What did James Chadwick’s experiments on the atom prove?

A

The existence of neutrons

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29
Q

Why do unstable nuclei give out radiation?

A

Unstable nuclei undergo decay to become more stable
As they release radiation their stability increases

30
Q

What is the name of the process in which an unstable nucleus gives out radiation to become more stable?

A

Radioactive decay

31
Q

Define the activity of an unstable nucleus

A

Activity is the rate of decay of a source of unstable nuclei

32
Q

What is the unit of radioactive decay?

A

Becquerel (bq)

33
Q

What is count-rate?

A

The number of radioactive decays per second for a radioactive source

34
Q

Give an example of a detector that may be used to measure count-rate?

A

Geiger-muller tube

35
Q

State four types of nuclear radiation

A

Alpha particles
Beta particles
Gamma rays
Neutrons

36
Q

What are the constituents of an alpha particle?

A

Two protons and two neutrons
It is the same as a helium nucleus

37
Q

What is the range of an alpha particle through air?

A

A few centimetres (2-10cm)

38
Q

What will stop beta radiation from passing through a point?

A

A thin sheet of aluminium
Several metres of air

39
Q

What will stop gamma radiation from passing through a point?

A

Several centimetres of lead
A few metres of concrete

40
Q

Which type of radiation is most ionising?

A

Alpha radiation

41
Q

Which type of radiation is least ionising?

A

Gamma radiation

42
Q

State any changes to mass or charge that occur due to the emission of a gamma ray

A

Both mass and charge remain unchanged

43
Q

Describe the nature of radioactive decay

A

Random
Which nuclei decays and when is determined only by chance
It is impossible to predict which nuclei will decay and when

44
Q

Define the half-life of a radioactive isotope

A

The time it takes for the number of unstable nuclei in a substance to halve
The time it takes for the count rate of a sample to fall to half its initial level

45
Q

What is radioactive contamination?

A

The presence of unwanted radioactive nuclei on other materials

46
Q

What is irridation?

A

The process of exposing a material to nuclear radiation
The material does not become radioactive

47
Q

Why is it important for the results of studies of the effects of radiation to be published and shared with other scientists?

A

To allow the findings to be independently checked

48
Q

Give four sources of background radiation

A

Rocks
Cosmic rays from space
Nuclear weapon testing
Nuclear accidents

49
Q

How should background radiation be dealt with in calculations?

A

The background count should be subtracted from any readings before calculations are attempted

50
Q

What is the unit used to measure radiation dosage?

A

Sieverts (Sv)

51
Q

How many millisieverts equal 1 sievert?

A

1000 millisieverts = 1 sievert

52
Q

Why might the radiation dosage that different people experience differ?

A

Some occupations involve working with radiation
Background radiations differs with location due to things such as the locality of nuclear power stations or radiation related testing

53
Q

What factor determines how dangerous a particular radioactive isotope is?

A

The half-life of the isotope

54
Q

Why are isotopes with long half-lives particularly harmful?

A

They remain radioactive for much longer periods of time
They must be stored in specific ways to avoid humans and the enviroment from being exposed to radiation for too long

55
Q

State two uses of nuclear radiation in the field of medicine

A

Examining of internal organs
Controlling and destroying unwanted tissue

56
Q

How is radiation used in sterilistation?

A

Gamma emitters are used to kill bacteria/parasites on equipment

57
Q

Explain the process of radiotherapy

A

Gamma emitters direct gamma rays at the cancerous cells
The cancerous cells absorb the radiation and are killed

58
Q

What is nuclear fission?

A

The splitting of large, unstable nuclei to form smaller more stable nuclei

59
Q

What usually needs to happen to induce fission?

A

The unstable nuclei must absorb a neutron
Spontaneous fission (where no neutron absorption occurs) is rare

60
Q

Alongside two smaller nuclei, what else is emitted in a fission reaction?

A

Two or three neutrons
Gamma rays
Energy

61
Q

What form of energy do all fission products have?

A

Kinetic energy

62
Q

What takes place during a chain reaction in a nuclear reactor?

A

An unstable nucleus absorbs a neutron
The nucleus undergoes fission and releases 2 or 3 further neutrons
These induce more fission, which results in a chain reaction

63
Q

What is the consequence of an uncontrolled chain reaction?

A

The rate of fission events becomes too high and results in the production of too much energy
This can lead to a nuclear explosion

64
Q

What are the three main components of the core of a nuclear reactor?

A

Fuel rods
Control rods
Moderator

65
Q

What is the role of the moderator in a nuclear reactor?

A

To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission

66
Q

How is the chain reaction in a fission reactor kept under control?

A

Control rods are positioned in between the fuel rods
The rate of fission is controlled by moving these rods up and down
The lower the rods are inserted, the slower the rate of fission

67
Q

What is nuclear fusion?

A

The joining of two light nuclei to produce a heavier nuclei and release energy

68
Q

Which releases more energy, nuclear fission or nuclear fusion?

A

Nuclear fusion

69
Q

Explain the difficulty of generating energy through nuclear fusion

A

Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them

70
Q

Explain why nuclear fusion is currently not a viable way to produce energy on Earth

A

With current equipment/techniques, the energy required is greater than the energy produced, resulting in a net energy loss

Physics (8 decks)

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