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Physics > Topic 4 - Atomic Structure > Flashcards

Topic 4 - Atomic Structure Flashcards

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1
Q

What can new experimental evidence of the atom lead to?

A

Scientific models being replaced or developed

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2
Q

Before the discovery of the electron, what were atoms thought to be?

A

Tiny spheres that could not be divided

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3
Q

What did the discovery of the electron lead to?

A

The plum pudding model of the atom - suggesting that the atom was a ball of positive charge with negative electrons embedded in it

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4
Q

What did the alpha particle scattering lead to?

A

The conclusion that the mass of an atom was concentrated at the centre and was charged (nucleus) - this nuclear model replaced the plum pudding model

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5
Q

How did Niels Bohr adapt the nuclear model?

A

He suggested that electrons orbit the nucleus at specific distances - the theory agreed with experimental observations

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6
Q

What happened after Niels Bohr adapted the nuclear model?

A

Experiments led to the idea that positive charge of the nucleus can be subdivided into a number of smaller particles each with the same amount (protons)

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7
Q

What did the experimental work of James Chadwick show?

A

Provided evidence of the existence of neutrons in the nucleus

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8
Q

When did James Chadwick release his experimental evidence?

A

20 years after the nucleus became an accepted scientific idea

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9
Q

What happened in the alpha scattering experiment?

A

Alpha particles were fired though a thin sheet of gold:

  • 99% went through (most of atom is empty space)
  • 1% were deflected (passed near a positive nucleus)
  • 1/10,000 bounced straight back (showing size of nucleus [1/10,000])
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10
Q

What happens to an unstable atomic nuclei?

A

The nucleus gives out radiation as it changes to become more stable (radioactive decay)

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11
Q

What is radioactive activity?

A

The rate at which a source of unstable nuclei decays

Measure in becquerel (Bq)

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12
Q

What is count-rate?

A

The number of decays recorded each second by a detector

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13
Q

Give an example of a count-rate detector.

A

Geiger-Muller tube

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14
Q

What are the three types of nuclear radiation emitted?

A 
Alpha particle (2 protons, 2 neutrons - like a helium nucleus) 
Beta particle (high speed electron released from nucleus as a neutron turns to a proton)
Gamma ray - electromagnetic waves
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15
Q

What are the features of an ALPHA particle?

A
  • 2 protons, 2 neutrons
  • charge = +2
  • mass = 4
  • range = 5-10 cm
  • stopped by: thin sheet of paper
  • ionisation: (very) will draw electrons - high charge + mass
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16
Q

What are the features of a BETA particle?

A
  • fast moving electron
  • charge = -1
  • mass = 1/2000
  • range = up to 1m
  • stopped by: thin sheet of aluminium (5mm)
  • ionisation: (low) repels electrons - low charge + mass
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17
Q

What are the features of a GAMMA ray?

A
  • electromagnetic waves
  • charge = 0
  • mass = 0
  • range = infinite
  • stopped by: thick lead
  • ionisation: won’t ionise unless it collides with an electron - no charge or mass
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18
Q

What do nuclear equations represent?

A

Radioactive decay

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19
Q

How will an alpha particle be represented in a nuclear equation?

A

4
(Alpha sign - backwards fish)
2

20
Q

How will a beta particle be represented in a nuclear equation?

A

0
e
-1

21
Q

What emission causes no change to the mass or charge of the nucleus?

A

Gamma rays

22
Q

What is the half-life of a radioactive isotope?

A

The time it takes for the count-rate from a sample containing the isotope to fall to half of its initial level

23
Q

Is radioactive decay random?

A

Yes

24
Q

What does a long half life mean?

A

The count rate falls more slowly because most of the nuclei don’t decay for a long time

25
Q

Is a long half life dangerous?

A

Yes

Nearby areas are exposed to radiation for millions of years

26
Q

How do you find half life on a graph?

A

Find the time interval (x-axis) that corresponds to half of the overall activity on the y-axis

27
Q

What is radioactive contamination?

A

The unwanted presence of materials containing radioactive atoms

28
Q

What is the hazard of radioactive contamination?

A

Due to the decay of the radioactive atoms - the type of radiation emitted affects the level of hazards

29
Q

What is irritation?

A

The process of exposing an object to nuclear radiation - the irritated object does not become radioactive

30
Q

What is the most dangerous radiation outside of the body?

A

Beta and gamma - can penetrate body and get to delicate organs (alpha can’t and is easily blocked by a small air gap)

31
Q

Inside the body, what is the most dangerous radiation?

A

Alpha - they do their damage in a localised area so contamination is the major concern

32
Q

Why is it important that reader has is published?

A

Because we understand how radiation affects our bodies, we can better protect ourselves.
Data is peer-viewed and will be quickly accepted leading to improvements in our use of radioactive sources

33
Q

Where does background radiation come from?

A
  • natural sources (;rocks and cosmic rays from space)

- man-made sources (;fallout from nuclear weapon testing and nuclear accidents)

34
Q

What affects background radiation dose?

A

Occupation and/or location

35
Q

Why do the hazards associated with radioactive material differ according to the half-life involved?

A

Radioactive isotopes have a wide range of half-life values - some will be long and therefore be exposed for millions of years, causing deformities and mutations in plants and animals

36
Q

What are nuclear radiations used for in medicine?

A
  • exploration of internal organs

- control or destruction of unwanted tissue

37
Q

What are the risks and benefits of radioactive

A

B: -gamma rays are directed carefully and in the right dosage to kill cancer cells without killing too many normal cells.
R: -damage is inevitably done to normal cells, making patient feel very ill

38
Q

What are the benefits and risks of medical tracers?

A

B: -can indicate whether internal structures are working as they’re supposed to, and diagnose life threatening conditions
R: - (small risk) cancer

39
Q

What is nuclear fission?

A

The splitting of large and unstable nucleus

40
Q

How often does fission occur?

A

Rarely - usually for fission to occur the unstable nucleus must first absorb a neutron

41
Q

What happens in nuclear fission?

A

The nucleus splits into two smaller nuclei, roughly equal sizes, and emits two or three neutrons plus gamma rays. Energy is released by fission reaction

42
Q

What do all fission products have?

A

Kinetic energy

43
Q

The neutrons may start a chain reaction, what is a chain reaction?

A

(Caused by neutrons) controlled in a nuclear reactor to control energy released.
E.g. Explosion caused by nuclear weapon is caused by an uncontrolled chain reaction

44
Q

What is nuclear fusion?

A

The joining of two light nuclei to form a heavier nucleus

45
Q

What happens in nuclear fusion?

A

Some mass may be converted into the energy of radiation

Physics (9 decks)

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