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y physics paper one > atomic structure > Flashcards

atomic structure Flashcards

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1
Q

What is the radius of an atom?

A

The radius of an atom is 1 x 10^-10 m.

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2
Q

What is the radius of a nucleus?

A

The radius of a nucleus is 1 x 10^-15 m.

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3
Q

Where does most of the mass of the atom come from?

A

Most of the mass of the atom is from the nucleus.

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4
Q

What are energy levels?

A

Electrons are arranged at different distances from the nucleus called energy levels.

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5
Q

How do electrons go up an energy level?

A

Electrons may absorb electromagnetic radiation and gain energy. They would then move to a higher energy level, further away from the nucleus.

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6
Q

How do electrons go down an energy level?

A

Electrons may release electromagnetic radiation and lose energy. They would then move to a lower energy level, closer to the nucleus.

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7
Q

What is the mass number?

A

The mass number is the sum of protons and neutrons in an atom.

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8
Q

What is the atomic number?

A

The atomic number is the sum of protons in an atom.

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9
Q

What are isotopes?

A

Isotopes of elements have the same atomic number (same protons and electrons) but a different mass number (different neutrons). Some are stable, but most of them aren’t stable.

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10
Q

What are ions?

A

Ions are elements that have gained or lost electrons.

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11
Q

What happens when isotopes are unstable?

A

When isotopes are unstable, they give off ionising radiation from the nucleus to become more stable, which ionises other atoms.

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12
Q

Before the discovery of the electron, what did people believe the atom was?

A

Before the discovery of the electron, people believed the atom was a tiny sphere that couldn’t be divided.

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13
Q

What did the discovery of the electron lead to? Who came up with this idea?

A

After the discovery of the electron, Thompson came up with the plum pudding model. This is a ball of positive charge with electrons embedded within. There was no nucleus or neutrons.

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14
Q

What experiment did Rutherford carry out? What were the three observations and conclusions from this experiment?

A

Rutherford carried out the alpha scattering experiment, where he fired a beam of alpha particles at thin gold foil.

  • most went straight through, so the atom is mostly empty space
  • some were scattered by small angles, so the nucleus is overall a positive charge
  • 1/8000 were sent straight back, so the positive charge is concentrated at the centre
  • therefore, the atom is a positive nucleus surrounded by a cloud of negative electrons
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15
Q

What did Niels Bohr suggest?

A

Niels Bohr suggested that electrons orbit the nucleus at different energy levels. He conducted experiments that agreed with this.

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16
Q

What did James Chadwick discover?

A

Chadwick discovered the neutron 20 years after the nucleus became an accepted idea.

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17
Q

What is activity? Give the units.

A

Activity is the rate at which a source of unstable nuclei decays (emits radiation). It is measured in becquerels (Bq). 1 Bq = 1 decay per second

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18
Q

What is count-rate?

A

Count-rate is the number of decays (radiation emitted) recorded each second by a detector. This will include background radiation. The count rate never reaches 0.

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19
Q

How is count-rate measured?

A

Count-rate is measured with a Geiger-Muller tube.

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20
Q

Name the four types of nuclear radiation.

A

nuclear radiation

  • alpha particle
  • beta particle
  • gamma rays
  • a neutron (n)
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21
Q

What is an alpha particle? Give the symbol.

A

An alpha particle is composed of two neutrons and two protons. This is identical to a helium (He) nucleus.
symbol - α

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22
Q

What is a beta particle? Give the symbol.

A

A beta particle is composed of one electron.

symbol - β

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23
Q

What is a gamma ray? Give the symbol.

A

A gamma ray is a wave of electromagnetic radiation, emitted from the nucleus.
symbol - γ

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24
Q

Rate alpha, beta and gamma from most to least penetrating.

A 
most penetrating
- gamma
- beta
- alpha
least penetrating
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25
Q

Rate alpha, beta and gamma from which can travel the furthest to shortest distance.

A 
furthest distance
- gamma
- beta
- alpha
shortest distance
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26
Q

Rate alpha, beta and gamma from most to least ionising.

A 
most ionising
- alpha (due to size)
- beta (due to size)
- gamma (due to passing through)
least ionising
27
Q

State what each form of nuclear radiation is stopped by.

A

nuclear radiation is stopped by…

  • alpha - paper
  • beta - thin aluminium
  • gamma - thick lead
28
Q

Describe how a beta particle is formed in the nucleus.

A

A beta particle forms when the nucleus is very unstable, so a neutron changes into a proton and a high-energy electron, which is repelled and fired from the nucleus as a beta particle.

29
Q

What do nuclear equations show?

A

Nuclear equations are used to represent radioactive decay. It is laid out like this…
atom before decay –> atom(s) after decay + radiation
The total mass and atomic numbers on each side must be equal!

30
Q

How is nuclear radiation written in nuclear equations?

A

alpha - 4 beta - 0
He e
2 -1

31
Q

State the nature of radioactive decay.

A

Radioactive decay is random.

32
Q

What is half-life? (two definitions)

A

Half-life is…

  • the time it takes for the number of radioactive nuclei of a radioactive isotope to halve
  • the time it takes for the count-rate from a sample to fall to half its initial level
33
Q

Fill in the gap:

the _____ the half-life, the more unstable the nuclei is

A

the shorter the half-life, the more unstable the nuclei is

34
Q

What is irradiation?

A

Irradiation is exposing an object to nuclear radiation, but the irradiated object doesn’t become radioactive.

35
Q

Name one way in which gamma radiation is useful.

A

Irradiating medical equipment with gamma rays can kill bacteria.

36
Q

Give one reason why ionising radiation is dangerous.

A

Ionising radiation can increase the risk of cancer and it can mutate body cells.

37
Q

Give two precautions to decrease the effects of ionising radiation.

A

precautions to decrease effects of radiation

  • shielding - lead walls, glass-screen, clothes
  • monitoring - measure radiation, stop when it is too dangerous
38
Q

What is radioactive contamination? Why is this hazardous?

A

Radioactive contamination is when unwanted radioactive isotopes end up of other materials. This is hazardous as the isotopes decay and emit ionising radiation, which can stay on or in you for many years.

39
Q

Why are alpha particles dangerous if they are contaminated?

A

Alpha particles are only dangerous is they are inside the body as outside, they are stopped by human skin. If they are inhaled or swallowed, the alpha particles crash into cells and damage their DNA, which causes a tumour cell (a mutated cell).

40
Q

Why are beta particles dangerous if they are contaminated?

A

Beta particles can penetrate the body, and cause mutated cells, so they are dangerous.

41
Q

Why are gamma rays not dangerous if they are contaminated?

A

Gamma rays pass through the body and do not mutate cells in the process, so they are not dangerous.

42
Q

What two pieces of equipment can be used to avoid radioactive contamination?

A

Gloves and tongs can be used to avoid radioactive contamination.

43
Q

What is background radiation?

A

Background radiation is low-level radiation that is around us all of the time. It should always be measured with a Geiger-Muller tube and then subtracted from results to find the true radiation of an object.

44
Q

Describe two forms of natural background radiation.

A

natural background radiation

  • radioactive rocks - like granite, in places in the UK like Cornwall, this is a major source of radiation
  • cosmic rays from space - high energy particles that travel through space and crash into the atmosphere, but the atmosphere protects us from some of it
45
Q

Describe two forms of man-made background radiation.

A

man-made background radiation

  • fall-out from nuclear weapon testing - releases radioactive isotopes into the environment for decades
  • nuclear accidents - like power stations
46
Q

What is the radiation dose measured in?

A

Radiation dose is measured in sieverts (Sv).

47
Q

State two uses of nuclear radiation.

A

uses of nuclear radiation

  • exploration of internal organs
  • control or destruction of unwanted tissues (radiotherapy)
48
Q

Describe how nuclear radiation is used to explore internal organs. Give an example.

A

Isotopes can be injected or swallowed, and a detector can then show where it is.
For example, iodine is absorbed in the thyroid gland, so it is mixed with radiation to check that it is still working.

49
Q

Give four properties required of the nuclear radiation for the exploration of internal organs.

A

properties of radiation for exploration of organs

  • must emit radiation that can pass out of the body
  • must not be strongly ionising to minimise cell damage
  • must not decay into another isotope
  • must have a short half-life so that it isn’t in the body for too long
50
Q

What is radiotherapy?

A

Radiotherapy is when gamma rays pass into the body to destroy a tumour.

51
Q

Why can radiotherapy be damaging? How can this risk be avoided?

A

Radiotherapy can damage healthy tissue as well. Therefore, radioactive rods are placed into the body by the tumour cells it is targeting, so the radiation targets the cells by the radioactive rods and there is less damage to healthy cells.

52
Q

Name three risks of radiation to the human body.

A

risks of radiation to body

  • can enter body cells and ionise the atoms within it, causing tissue damage
  • low doses of radiation can cause minor damage to cells, which can pave way to mutant cells, which can then divide uncontrollably, causing cancer
  • higher doses of radiation can kill cells completely, which causes tiredness, vomiting and hair loss
53
Q

What is nuclear fission?

A

Nuclear fission is the splitting of large and unstable nuclei.

54
Q

What two nuclei are usually used in nuclear fission?

A

nuclei used in nuclear fission

  • uranium (U-235)
  • plutonium (P-239)
55
Q

What is required for nuclear fission to begin?

A

A neutron is usually fired at a nucleus so that it can absorb it. This is how fission begins. For this reason, spontaneous fission is rare.

56
Q

Describe the process of nuclear fission.

A

nuclear fission

1) neutron is fired at U-235 or P-239
2) neutron is absorbed
3) U-235 or P-239 splits into two roughly equal smaller nuclei and emits 2 or 3 neutrons and gamma rays
- energy is released as all of these products have kinetic energy
4) neutrons may go on to start a chain reaction

57
Q

How is nuclear fission used to power nuclear power plants?

A

The energy produced in nuclear fission is used to heat water. This then forms steam, which turns turbines to produce power.

58
Q

How is the rate of nuclear fission controlled?

A

Nuclear fission is controlled with control rods, which are lowered when the rate is dangerously fast. They absorb neutrons.

59
Q

How do nuclear weapons explode?

A

Nuclear weapons explode as they are uncontrolled nuclear fission reactions.

60
Q

What is nuclear fusion?

A

Nuclear fusion is the fusing of two lighter nuclei into one heavier nucleus. For this reason, it is NOT a chain reaction.

61
Q

How does nuclear fusion convert energy?

A

Some of the mass of the lighter nuclei is converted to energy, which is released as radiation.

62
Q

Why is nuclear fusion hard to do?

A

Nuclear fusion releases more energy than nuclear fission, so it is desired on earth. However, it is hard to do as it is expensive, requires high temperatures and pressures. It is also dangerous for these reasons.

63
Q

Where does nuclear fusion occur?

A

Nuclear fusion occurs naturally in stars.

y physics paper one (5 decks)

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