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physics - atomic structure Flashcards

1
Q

How did Democritus (first person to conceive atomic theory) describe atoms

A
  • The smallest possible unit of matter
  • Small spheres
  • Separated from each by empty space
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2
Q

In the 1800s how did John Dalton describe atoms

A

John described atoms as solid spheres and suggested that different types of spheres make up the different elements

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3
Q

Describe the plum pudding model

A

An atom consisted of a ball of positive charge with negative electrons embedded through it

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4
Q

How did Rutherford develop the nuclear model

A

Alpha particles were fired at a thin sheet of gold foil. Most particles passed through, but some were deflected off course. This caused him to hypothesise that there was a dense region of positive charge at the centre of the atom that repelled the alpha particles. As a result he developed the nucleas model of the atom, in which there was a central positive nuclear, surrounded by negative electrons.

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5
Q

What did Bohr suggest

A

That electrons orbit the nucleus in shells

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6
Q

Describe the stability of isotopes. What happens if isotopes are unstable?

A

some isotopes are unstable and can decay into other elements. Decay involves emitting radiation such as alpha, beta, and gamma radiation

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7
Q

Describe the different energy levels of the shells

A

Electrons orbit the nucleus at specific energy levels which are also called shells. The shells get progressively further from the nucleus and increase in energy level. Electrons can absorb electromagnetic radiation and jump to a higher energy level. These electrons can later fall back down to a lower energy level and emit electromagnetic radiation in the process. Electrons can also absorb enough energy to leave the atom altogether which is known as ionisation.

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8
Q

What is a radioactive material

A

Means it has unstable isotopes that can decay

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9
Q

What does an alpha particle consist of

A

Two protons and two neutrons - It is the same as a helium nucleus and has no electrons and has a charge of 2+

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10
Q

What does a beta particle consist of

A

One electron

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11
Q

What does a gamma ray consist of

A

electromagnetic radiation

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12
Q

What causes the emission of a neutron

A

A nucleus has too many neutrons making it unstable

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13
Q

How penetrative is an alpha particle

A

lowly penetrating - cannot penetrate paper

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14
Q

How penetrative is a beta particle

A

somewhat penetrating - can pass through paper but not 5mm of aluminium

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15
Q

How penetrative are Gamma Rays

A

Highly penetrating - can pass through aluminium but not thick lead

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16
Q

What does ‘activity’ mean in terms of half life

A

The overall rate of decay of all of the radioactive isotopes a sample

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17
Q

How do we measure radioactive activity

A

average number of decays per second in Becquerels (Bq)

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18
Q

What are the two definitions of a half life

A

The time taken for the activity to half
The time taken for the number of radioactive nuclei in a sample to halve

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19
Q

What device is used to record radioactive decays

A

Geiger-Muller tube and counter

20
Q

What is irradiation

A

The process by which objects are exposed to radiation

21
Q

What is contamination

A

Contamination is when radioactive particles get onto your body or other objects

22
Q

What factors determine how harmful the radiation is?

A

The amount of radiation you receive
The type of radiation
Where your exposed to the radiation

23
Q

What happens if your DNA is exposed to ionising radiation

A
  • The DNA could mutate
  • The cell could divide uncontrollably and become cancerous
  • The DNA could be destroyed
24
Q

Which radioactive substance is the most harmful inside the body and why

A

Alpha particles because it is the most ionising

25
Q

What factors affect the amount go radiation you receive

A
  • How long your exposed for
  • How radioactive the substance is
  • How far away from the source you are
26
Q

What will happen to cells that receive a large dosage of radiation

A

The cells will die

27
Q

What are the three symptoms of radiation sickness

A
  • Tiredness
  • Hairloss
  • Vomiting
28
Q

why can exposure to low levels of radiation over long periods of time lead to cancer

A

Radiation can cause mutations in our DNA which may cause our cells to divide uncontrollably

29
Q

What is radiotherapy

A

Radiotherapy is the use of targeted doses of radiation to kill cancerous cells

30
Q

What is external radiotherapy

A

Where the cancerous cells are exposed to gamma radiation from outside of the body, from lots of different angles so only the cancer site gets the highest dose of radiation

31
Q

What is internal radiation

A

Where the cancerous cells are exposed to radiation from inside the body. The radiation source usually emits beta particles, and is placed inside or near the cancer cells.

32
Q

What are the side effects to radiotherapy

A

The patient feels sick
The radiation also kills healthy cells

33
Q

How do medical tracers work

A

A radioactive isotope (tracer) is injected or swallowed by a person. If the tracer is injected, the tracer will travel to parts if the body through the blood> If the tracer is swallowed the tracer may be absorbed through the persons intestine and then travel via the bloodstream. In both cases the position of the tracer can be detected from outside the body because it emits radiation. We can use this technique to ‘see’ the movement and accumulation of the tracer inside the body.

34
Q

What are medical tracers used for

A

help diagnose medical problem and allow us to locate or track things such as tumours within the body

35
Q

What is nuclear fission

A

The splitting up of a large and unstable nuclei into smaller nuclei

36
Q

How can nuclear fission occur

A

By an atom’s nucleus absorbing a neutron and becoming even more unstable. The neutron helps to split the nucleus

37
Q

Steps for a nuclear fission chain reaction

A

It start with an unstable nucleus like uranium-235. A neutron is then fired at the unstable nucleus and causes it to split apart,. The unstable nucleus splits into two ‘daughter’ nuclei and two or three neutrons, while also emitting lots of energy In the form of gamma radiation. The two or three neutrons that were released are then absorbed by the other unstable nuclei and this repeats the process. This process then occurs over and over again in what we call a chain reaction.

38
Q

What happens to the gamma radiation that is released in nuclear fission

A

The gamma radiation is used to heat liquid water into steam. As the steam rises it turns turbines and the kinetic energy of those turbine is converted into electricity by a generator.

39
Q

How are nuclear reactors kept under control

A

To help keep the reaction stable, we can lower control rods into the nucleus reactor which absorbs neutrons and slows down the reaction

40
Q

What are the main pros of nuclear power

A

They can produce large and steady electric power
Nuclear fuel like uranium or plutonium is relatively cheap
Doesn’t produce any greenhouse gases

41
Q

Major cons of nuclear energy

A

Expensive to build
Waste is radioactive and very expensive to get to store
There is a risk of a nuclear meltdown

42
Q

What is nuclear fusion

A

Nuclear fusion is the fusing of two lighter nuclei to make a single heavier nucleus. When this occurs, a lot of energy is emitted in the form of electromagnetic radiation

43
Q

Where does the energy released by nuclear fission come from?

A

Some of the mass converts to energy

44
Q

Where does nuclear fusion occur

A

Nuclear fusion occurs in stars and is the reason why stars give off so much energy. Most of the fusion occurring in stars is hydrogen nuclei fusing to become helium nuclei

45
Q

Why does nuclear fusion only happen at very high temperatures and pressures

A

To overcome the repulsion of the positively charged nuclei

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