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Physics GCSE Y11 (F) > P4: Atomic structure > Flashcards

P4: Atomic structure Flashcards

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1
Q

What was Dalton’s model of the atom?

A

Atoms were solid, indivisible spheres. Each element was made of a different type of sphere.

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2
Q

What was Thomson’s model of the atom?

A

Discovered electrons which could be removed from atoms- disproving Dalton’s theory of indivisibility. Thomson suggested atoms were spheres of positive charge, with negative electrons scattered throughout (plum pudding model).

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3
Q

What was Rutherford’s model of the atom?

A

Positively charged nucleus, surrounded by a cloud of negative electrons. This was the first nuclear model of the atom.

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4
Q

What discovery did Bohr make? How was he proven right?

A

Electrons orbit the nucleus in fixed positions, called energy levels. His theoretical calculations agreed with experimental data.

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5
Q

What discovery was made after electron orbits?

A

Experiments showed that the nucleus’ positive charge was subdivided between a group of particles, called protons.

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6
Q

What discovery did Chadwick make? Why did this make sense?

A

He proved the existence of neutrons in the nucleus. This explained the imbalance between the atomic and mass numbers.

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7
Q

How was Rutherford’s alpha scattering experiment conducted?

A

Scientists in Rutherford’s lab fired a beam of alpha particles at a thin sheet of gold foil.

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8
Q

The nucleus’ radius is about ___x smaller than the radius of an atom.

A

10,000x

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9
Q

The radius of an atom is about ___m.

A

1x10(^-10)m

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10
Q

What are isotopes?

A

Isotopes of an element are atoms with the same number of protons, but different numbers of neutrons (so have different mass numbers).

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11
Q

All elements have isotopes, but…

A

…but there are usually only one or two stable ones.

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12
Q

What do unstable isotopes tend to do?

A

They decay into other elements, giving out radiation to become more stable. This process is called radioactive decay.

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13
Q

What is radioactive decay?

A

The process by which unstable nuclei emit radiation until they reach a stable state.

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14
Q

What types of radiation do unstable nuclei release?

A

Alpha, beta, gamma, neutron.

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15
Q

What makes a nucleus unstable?

A

A bigger nucleus would be less stable because it’s harder to hold all the protons and neutrons together. The less energy holding them together, the less stable.

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16
Q

What is alpha radiation?

A

A particle: helium nucleus (2 protons, 2 neutrons).

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17
Q

What is the mass and charge of alpha particles?

A

Relative mass: large. Charge: +2e

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18
Q

What is the ionising power of alpha radiation?

A

High

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19
Q

Alpha particles can be blocked by…

A

…paper or skin.

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20
Q

What is beta radiation?

A

A particle: high speed electrons released by the nucleus.

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21
Q

What is the mass and charge of beta particles?

A

Small relative mass. Charge: -1e

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22
Q

What is the ionising power of beta radiation?

A

Moderate to low.

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23
Q

Beta radiation can be blocked by…

A

…thin sheet of aluminium and lead.

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24
Q

What is gamma radiation?

A

It is a high energy, high frequency electromagnetic wave (of photons). Released by the nucleus to get rid of excess energy.

25
Q

What is the mass and charge of gamma rays?

A

No mass and no charge.

26
Q

What is the ionising power of gamma radiation and why?

A

Very low, because it has no mass or charge.

27
Q

Gamma radiation can be “absorbed” by…

A

several cm of lead / several m of concrete

28
Q

What is ionisation?

A

The process by which radiation from radioactive substances ionise (knock electrons out of) atoms.

29
Q

What does ionisation of body cells lead to?

A

Cell death and cancers.

30
Q

Which type of radiation is the most ionising?

A

Alpha.

31
Q

Alpha decay decreases the ___ and ___ of the nucleus.

A

Charge and mass.

32
Q

When an atom emits an alpha particle, its atomic number reduces by __ and and its mass number reduces by __.

A

2, 4

33
Q

What is the rule to remember when forming nuclear equations?

A

Total mass and atomic numbers must be equal on both sides of the equation.

34
Q

How can alpha particles be shown in nuclear equations?

A

(4,2)α or (4,2)He

35
Q

What happens during beta decay?

A

A neutron in the nucleus turns into a proton and releases a fast-moving electron.

36
Q

How are beta particles represented in nuclear equations?

A

(0, -1)e or (0, -1)β

37
Q

How are gamma rays represented in nuclear equations?

A

(0,0)γ

38
Q

How can radiation be measured?

A

With a Geiger-Muller tube and counter, which records the count-rate.

39
Q

Radioactive decay of a nucleus cannot be ___ ___; it is ___. Half-life can be used to make___ ___ about radioactive sources.

A

1) accurately predicted
2) random
3) estimated predictions

40
Q

What is activity and what is it measured in?

A

The number of decays per second- measured in Becquerels, Bq, where 1Bq is one decay per second.

41
Q

What is the half-life of a radioactive isotope?

A

The time it takes for half the nuclei in the sample to decay, or for the activity to halve.

42
Q

What three things contribute to background radiation?

A

1) Radioactivity of naturally occuring unstable isotopes.
2) Radiation from space: cosmic rays.
3) Radiation due to human activity.

43
Q

What is radiation dose measured in?

A

Sieverts (Sv) or millisieverts (mSv)

44
Q

What is irradiation?

A

Exposure to radiation.

45
Q

When working with radioactive sources, what are two ways to prevent irradiation?

A

1) Keeping sources in lead-lined boxes.

2) Staying behind barriers/in a different room and controlling the source remotely.

46
Q

What is contamination?

A

The presence of radioactive materials in/on an object.

47
Q

Why is contamination more dangerous than irradiation?

A

A contaminated object will be exposed to radiation for as long as it is contaminated, whereas, if irradiated, it stops being exposed to radiation as soon as it is no longer near the source.

48
Q

What three things are used to prevent contamination?

A

1) Gloves
2) Tongs
3) Protective suits

49
Q

Why are gamma emitters used in medical tracers?

A

Gamma is used so that radiation passes through the body without causing too much ionisation.

50
Q

Why should gamma emitters used in medical tracers have a short half-life?

A

So that radioactivity inside a patient quickly minimises, preventing too much ionisation.

51
Q

How does radiotherapy work? Give 2 methods.

A

1) Gamma rays are directed carefully, and at the right dosage, to kill cancer cells without damaging too many normal cells.
2) Radiation (usually beta) emitting implants are put next to/inside tumours.

52
Q

Why does radiotherapy make patients feel ill?

A

Damage is done to non-cancerous cells in the process of killing cancerous ones.

53
Q

Explain how contamination leads to cell death and cancer.

A

When radiation enters the body, it causes ionisation of atoms and molecules in tissue.
Lower doses of radiation lead to mutated cells which divide uncontrollably, i.e. cancer.
Higher doses cause cell death, which can lead to radiation sickness.

54
Q

Explain what happens during induced nuclear fission.

A

1) High-energy neutron fired at unstable nucleus.
2) Nucleus absorbs neutron and becomes more unstable.
3) Nucleus splits into 2, releasing 2+ neutrons and… 4) Energy not transferred to the KE stores of the products is carried away by gamma rays.
5) If any of the released neutrons are moving enough, they can be absorbed by another nucleus and cause it to split, i.e. a chain reaction.

55
Q

How is nuclear fission controlled?

A

Lowering down control rods into a nuclear reactor. These absorb neutrons, slowing the chain reaction and controlling the amount of energy released.

56
Q

What happens during uncontrolled fission reactions?

A

Lots of energy is released as an explosion (this is how nuclear weapons work).

57
Q

What happens during nuclear fusion?

A

1) Two small, high-speed nuclei collide and fuse into a larger nucleus.
2) This nucleus is less massive than the total mass of the two initial nuclei. Some of their mass is converted to energy and released as radiation.

58
Q

For a given mass of fuel, which of nuclear fission and fusion produces more energy?

A

Fusion.

59
Q

Although nuclear fusion produces more energy than fission per unit mass of fuel, it can’t be used to generate energy. Why is this?

A

The temperatures and pressures needed for fusion are so high that fusion reactors are difficult and expensive to build.

Physics GCSE Y11 (F) (9 decks)

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