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Physics Paper 1 > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

What is the radius of an atom?

A

Around 1x10^-10 metres

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2
Q

What is the basic structure of an atom?

A

A positively charged nucleus made of protons and neutrons surrounded by negatively charged electrons.

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3
Q

What is the radius of a nucleus?

A

Less than 1/10000 of the radius of an atom

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4
Q

Where is most of the mass of an atom concentrated?

A

Nucleus

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5
Q

How are electrons arranged in an atom?

A

At different distances from the nucleus (different energy levels).

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6
Q

How do electron arrangements change?

A

With the absorption of electromagnetic radiation (move further from nucleus) or by emission of electromagnetic radiation (move closer to the nucleus, lower energy level).

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7
Q

What does an atom that loses electrons become?

A

A positive ion.

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8
Q

What does an atom that gains electrons become?

A

A negative ion.

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9
Q

What is the relative change of a:
Proton
Neutron
Electron ?

A

1
0
-1

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10
Q

What is the relative mass of a:
Proton
Neutron
Electron?

A

1
1
0.0005

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11
Q

In an atom, the number of electrons=

A

Number of protons

Meaning that atoms have no overall charge.

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12
Q

What is the atomic number?

A

Number of protons

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13
Q

What is the mass number?

A

Total number of protons and neutrons.

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14
Q

What are isotopes?

A

Atoms of the same element that have different numbers of neutrons.

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15
Q

What do all isotopes of an element contain?

A

The same number of protons, otherwise they would be different elements. It is the number of neutrons that are different.

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16
Q

What were atoms thought to be before the discovery of the electron?

A

Tiny spheres that could not be divided.

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17
Q

What did the discovery of the electron lead to?

A

The plum pudding model of the atom which suggested that the atom is a ball of positive charge with negative electron embedded in it.

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18
Q

Which conclusion did the results from the alpha particle scattering experiment lead to?

A

The conclusion that the mass of an atom was concentrated at the nucleus and that the nucleus was charged. This nuclear model replaced the plum pudding model.

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19
Q

How did Neil Bohr adapt the nuclear model?

A

By suggesting that electrons orbit the nucleus at different distances. The theoretical calculations of Bohr agreed with experimental observation.

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20
Q

What did later experiments of atoms lead to?

A

The idea that the positive charge of any nucleus could be subdivided into a whole number of small particles, each particle having the same amount of positive charge. The name proton was given to these particles.

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21
Q

What did the experimental work of James Chadwick provide?

A

The evidence to show the existence of neutron within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.

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22
Q

What is nuclear decay?

A

Some atomic nuclei are unstable, the nucleus gives out radiation as it changes to become more stable.

23
Q

What sort of process is nuclear decay?

A

A random process

24
Q

What is the activity of a radioactive source?

A

The rate at which it decays.

25
Q

What is activity measured in?

A

Becquerels (Bq)

One Becquerel= one decay per second

26
Q

What is a count rate?

A

The number of decays recorded each second by a detector (e.g. Geiger- Muller tube)

1 becquerel = 1 count per second

27
Q

Nuclear radiation may be emitted by:

A
  • An alpha particle
  • A beta particle
  • A gamma ray
  • A neutron
28
Q

What is radioactive contamination?

A

The unwanted presence of materials containing radioactive atoms in other materials.

29
Q

What is the hazard from contamination due to?

A

To the sexy of the contaminating atoms.

30
Q

What is irradiation?

A

The process of exposing an object to nuclear radiation. It can deliberate or accidental and does not cause the object to become radioactive.

31
Q

How can you protect yourself against irradiation when using radioactive sources?

A
  • Using sources of the lowest activity possible for the shortest time possible.
  • Wearing protective clothing such as a lead apron.
  • Not handle sources with bare hands.
32
Q

What is the half life of a radioactive isotope?

A

The time it takes for the number of nuclei of the isotope in a sample to halve it the count rate from a sample containing the isotope to fall to half its initial level.

E.g. an isotope takes 25 minutes to fall from 40-80 so the half life is 25.

33
Q

How can the half-life of different isotopes vary?

A

From less than a second to a million years.

The half life of a particular radioactive isotope does not change.

34
Q

Isotopes with a short half life:

A
  • Very unstable, emit radiation quickly so exposure can be hazardous.
  • Do not remain radioactive for very long.
35
Q

Isotope with a long half life:

A
  • More stable and remain radioactive for a very long time

- Emit radiation slowly, so exposure is less hazardous.

36
Q

How do medical tracers to look at internal organs use nuclear radiation?

A
  • Radioactive isotope is ingested/ injected into the body

- As it travels around the body, it can be detected in the outside.

37
Q

How can nuclear radiation be used to look for damage or blockages in the intestines?

A
  • if there is a blockage, then radioactivity cannot be detected after the blockage
  • if the intestines are damaged the radioactive source can be seen to pass out of the intestines into other areas of the body.
38
Q

How can nuclear radiation be used to treat tumours?

A
  • A tumour in the thyroid gland could be tested with radioactive iodine, which gathers in the gland and destroys nearby cells
  • A focussed beam of gamma rays can be used to destroy some tumours
39
Q

Why would a gamma source make the best tracer?

A

They can penetrate the body and be detected on the outside. They are the least ionising.

40
Q

Where does background radiation come from?

A
  • Natural sources such as rocks and cosmic rays from space.

- Man made sources s if h as the fall out from nuclear weapons testing and nuclear accidents.

41
Q

How can the level of background radiation and radiation dose be affected?

A

By occupation and/or location

42
Q

What is radiation dose measured in?

A

Sieverts (Sv)

Sievert= 1000 millisieverts

43
Q

What is nuclear fission?

A

The splitting of a large unstable nucleus into two smaller nuclei which releases energy the isotopes most used are uranium and plutonium.

44
Q

When will fission usually occur?

A

By itself- usually the unstable nucleus must absorb a neutron first.

45
Q

During fission, the nucleus:

A
  • Splits into two smaller nuclei of roughly equal size

- Emits 2 or 3 neutrons, gamma rays and energy

46
Q

What do all of the products of fission have?

A

Kinetic energy

47
Q

What do the neutrons that are emitted from fission go on to do?

A

Make a chain reaction by being absorbed by other large, unstable nuclei.

48
Q

In a chain reactor what happens to a chain reaction?

A

The chain reaction is controlled to give a steady release of energy. The explosion caused by a nuclear weapon is the result of an uncontrolled chain reaction.

49
Q

During nuclear fusion:

A

Two nuclei join together to form a heavier nucleus.

- Some of the mass is converted into energy and some of this energy may be emitted as radiation.

50
Q

Why does nuclear fusion require high temperatures and pressures?

A

To overcome electrostatic repulsion and to bring the positive nuclei close enough together for fusion to take place.

51
Q

When an alpha particle is emitted:

A

Mass number reduced by 4
Atomic number reduced by 2

Because 2 protons and 2 neutrons are emitted from the nucleus.

52
Q

With beta decay:

A

Mass number does not change
Atomic number increases by 1

Because a neutron turns into a proton and an electron and the electron is emitted as the beta particle.

53
Q

Gamma ray emission:

A

Does not cause a change.

Physics Paper 1 (4 decks)

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