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Physics > Atomic Structure > Flashcards

Atomic Structure Flashcards

1
Q

What is the order of the scientists versions of the atom

A

Democritus (atomic theory)

1804 John Dalton - matter was made up of tiny spheres that couldnt be broken up but each element was made up of a different type of atom

JJ Thompson - Plum pudding model and electrons could be removed from atom.

Ernest Rutherford - First Nuclear model (nucleus discovered (alpha scattering experiment))

Neil’s Bohr - Second Nuclear model (Planetary model) -Electrons orbit the nucleus in energy levels

James Chadwick - Existence of neutrons in nucleus

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2
Q

What were the discoveries of the alpha particle scattering experiment

A

The mass of the atom is concentrated at the nucleus.

The nucleus is small and positively charged

Most of the atom is empty space

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3
Q

What is the approximate size of the radius of an atom?

A

1 ×10-¹⁰m

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4
Q

What is radioactive decay and why does it happen?

A

Radioactive decay is when unstable isotopes decay into other elements and give out radiation as they try to become more stable.

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5
Q

How can you infer when the nuclei will decay?

A

You can’t.

It is a random process so you never know which will decay first and you cannot change the rate of how they decay as it is not affected by physical conditions like temperature.

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6
Q

What is ionising radiation?

A

Ionising radiation is radiation that knocks electrons off atoms creating positive ions.

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7
Q

What are the three different types of ionising radiation

A

Alpha decay
Beta decay
Gamma decay

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8
Q

What is alpha decay

A

When an alpha particle is emmited from the nucleus.

2 protons and 2 neutrons are lost from ht nucleus
So…

The atomic number decreases by 2 and the mass number decreases by 4

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9
Q

What are alpha particles

A

Two neutrons and two protons
(Same as a helium nucleus)

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10
Q

State the properties of an alpha particle (5)

A

Big, heavy, slow-moving
Do not penetrate very far into materials
Stopped quickly
Absorbed by a sheet of paper

Strongly ionising (bash into alot of atoms)

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11
Q

What is beta decay

A

A nuetron will turn into a proton in the nucleus, which increases the atomic number by +1 but decreases the mass number by 1

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12
Q

What is a beta particle

A

A fast moving electron (charge: -1 mass: 0)

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13
Q

Where is most of the mass of an atom concentrated?

A

In the nucleus.

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14
Q

What type of charge does the nucleus of an atom have? Why?

A

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

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15
Q

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

A
  1. Absorbing electromagnetic radiation
  2. Emitting electromagnetic radiation
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16
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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17
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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18
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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19
Q

What is an atom’s mass number?

A

The total number of protons and
neutrons in the atom

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20
Q

What is an isotope of an atom?

A

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

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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

Which experiment led to the plum-pudding model being discarded?

A

Rutherford’s alpha-scattering
experiment.

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23
Q

Why do unstable nuclei give out radiation? (2)

A

● Unstable nuclei undergo decay to
become more stable

● As they release radiation their stability increases

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24
Q

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

A

Radioactive decay

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25
Q

Define the activity of an unstable nucleus.

A

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

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26
Q

What is the unit of radioactive activity?

A

Becquerel (Bq)

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27
Q

What is count-rate?

A

The number of radioactive decays per second for a radioactive source.

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28
Q

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

A

Geiger-Muller tube

29
Q

State four types of nuclear radiation.

A
  1. Alpha particles
  2. Beta particles
  3. Gamma rays
  4. Neutrons
30
Q

What are the constituents of an alpha particle? (2)

A

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

31
Q

What is the range of an alpha particle through air?

A

A few centimetres (normally in the range of 2-10cm).

32
Q

What will stop beta radiation from passing through a point? (2)

A

● A thin sheet of aluminium
● Several metres of air

33
Q

What will stop gamma radiation from passing through a point? (2)

A

● Several centimetres of lead
● A few metres of concrete

34
Q

Which type of radiation is most ionising?

A

Alpha radiation

35
Q

Which type of radiation is least ionising?

A

Gamma radiation

36
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.

37
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

38
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
from a sample to fall to half its initial
level

39
Q

What is radioactive contamination?

A

The presence of unwanted radioactive nuclei on other materials.

40
Q

What is irradiation?

A

● The process of exposing a material to nuclear radiation

● The material does not become
radioactive

41
Q

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

A

● To allow the findings to be
independently checked

● This is known as peer review

42
Q

Give 4 sources of background radiation.

A
  1. Rocks
  2. Cosmic rays from space
  3. Nuclear weapon testing
  4. Nuclear accidents
43
Q

How should background radiation be dealt with in calculations?

A

The background count should be
subtracted from any readings before calculations (half life etc.) are attempted.

44
Q

What is the unit used to measure radiation dosage?

A

Sieverts (Sv)

45
Q

How many millisieverts equal 1 sievert?

A

1000 millisieverts = 1 sievert

46
Q

Why might the radiation dosage that different people experience differ?

A

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

47
Q

What factor determines how dangerous a particular radioactive isotope is?

A

The half-life of the isotope.

48
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 environment from being exposed to radiation for too long

49
Q

State two uses of nuclear radiation in the field of medicine.

A
  1. Examining of internal organs
  2. Controlling and destroying unwanted tissue
50
Q

How is radiation used in sterilisation?

A

Gamma emitters are used to kill
bacteria/parasites on equipment

51
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

52
Q

How are medical tracers chosen? (2)

A

They should have a short half life and decay into a stable isotope which can be excreted.

They should only release gamma radiation since it is weakly ionising and can easily pass through body tissue without damaging it.

53
Q

What is nuclear fission?

A

The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons)

54
Q

Give an example of a fissionable isotope.

A

Uranium - 235

55
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

56
Q

Alongside two smaller nuclei, what else is emitted in a fission reaction? (3)

A

● Two or three neutrons
● Gamma rays
● Energy

57
Q

What form of energy do all fission products have?

A

Kinetic energy.

58
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

59
Q

What is the consequence of an uncontrolled chain reaction?

A

● The rate of fission events becomes to high and results in the production of too much energy

● This can lead to a nuclear explosion

60
Q

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

A
  1. Fuel rods
  2. Control rods
  3. Moderator
61
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.

62
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

63
Q

What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?

A

Fissile Nuclei

64
Q

What is nuclear fusion?

A

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

65
Q

Name two isotopes of hydrogen which are commonly used in nuclear fusion.

A

Deuterium and Tritium

66
Q

Which releases more energy, nuclear fission or nuclear fusion?

A

Nuclear fusion

67
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.

68
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 (4 decks)

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