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Science Spec Flaschcards > P4 > Flashcards

P4 Flashcards

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1
Q

Characteristics of an atom

A

Items are very small, having a radius of about 1×10^-10 metres

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2
Q

What is the basic structure of an atom?

A

A positively charged nucleus composed of both of protons and neutrons surrounded by negatively charged electrons

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3
Q

What is the radius of the nucleus?

A

The radius of a nucleus is less than 1/10000 of the radius of an atom, most of the mass of an atom is concentrated in the nucleus

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4
Q

How do the electron arrangements change?

A
  • The electrons arranged at different distances from the brackets (different energy levels).
  • The electron arrangement may change with the absorption of electromagnetic magnetic radiation move (further from the nucleus; a higher energy level) or by the invention of electromagnetic radiation (move closer to the nucleus; a lower energy level)
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5
Q

What charge do atoms have and why?

A

Atoms have no overall electrical charge as in an atom, the numbers of electrons is equal to the number of protons in the nucleus

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6
Q

What is the mass number of an element?

A

The total number of protons and neutrons in an atom

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7
Q

What is the atomic number of an element?

A

The number of protons and electrons in the atom

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8
Q

What are isotopes?

A

Isotopes of an element are atoms with the same number of protons (the same atomic number, and so the same charge on the nucleus) but a different number of neutrons (a different mass number). E.g. (18top 8bottom)O is an isotope of oxygen.

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9
Q

If elements lose electrons in their outer shell what do the atoms turn into?

A

Positive ion

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10
Q

What are similarities in the same isotopes?

A

They share similar chemical properties

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11
Q

All elements have different isotopes, though how many stable isotopes are there?

A

One or two

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12
Q

Note:

A

Go to page 196 and see how isotopes are

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13
Q

What do new experimental evidence do to scientific models?

A

Leads them to be changed or replaced

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14
Q

What were electrons thought to be before its discovery?

A

Atoms were thought to be tiny spheres that could not be divided (this was before 1897)

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15
Q

What happened after the discovery of the electron (1897)?

A
  • The discovery of the electron led to the plum pudding model of the atom
  • JJ Thompson suggested The plum pudding model, that the atom is a pool of positive charge with negative electrons embedded in it
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16
Q

What happened in 1909 with Rutherford’s experiment?

A
  • They conducted the famous alpha particle scattering experiments
  • They fired positively charged alpha particles at an extremely thin sheet of gold
  • From the plum pudding model,they were expecting the particles to pass straight through the sheet or be slightly deflected at most
  • This was because the positive charge of each atom was though to be very spread out through the pudding of the atom
  • But,whilst most of the particles did go straight through the sheet,some were deflected more than expected,and a small number were deflected backwards
  • So the plum pudding model could not be right
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17
Q

What did the Rutherford experiment do as a result?

A

The results from the alpha particle scattering experiment lead to the conclusion that the mass of an atom is concentrated at the centre (nucleus), and that the nucleus was charged this nuclear model replace the pump pudding model

The nuclear model of the atom.In this a tiny,positive charged nucleus at the centre,where most of the mass is concentrated.A ‘cloud’ of negative electrons surrounds this nucleus - so most of the atom is empty space.

These were the conclusions because even though most alpha particles passed through, some bounced back.

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18
Q

What did Niels Bohr do to the nuclear model?

A
  • He adopted the nuclear model by suggesting that electrons orbit, the nucleus at specific distances
  • The theoretical calculations of Bohr agreed with the experimental observations
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19
Q

What did James Chadwick discover in 1932?

A

About 20 years after the idea of a nucleus was accepted, in 1932, James Chadwick proved the existence of the neutron, which explained the imbalance between the atomic and mass numbers

20
Q

The differences between the plum pudding model of the atom and the nuclear model of the atom

A
  • Plum pudding model mass is distributed evenly
  • Plum pudding model is a solid mass
  • Plum pudding electrons embedded in the mass of positive charge
  • Nuclear model positive charge occupies only a small part of the atom
  • Nuclear model electrons orbit some distance from the centre
  • Nuclear model the atom is mainly empty space
  • Nuclear model mass is concentrated in the centre
21
Q

As some nuclei are unstable, what does this lead to?

A

The other unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable (they fry to balance the number of protons and neutrons in their nucleus or get rid of any excess energy). This process is called radioactive decay

22
Q

What is activity?

A

Activity is the richest source of unstable nuclei decays. Activity is measured in becquerel(Bq)

23
Q

What is count-rate?

A

Count-rate is the number of decays recorded each second by a detector (e.g Geiger-Müller tube)

24
Q

What are the different types of nuclear radiation?

A
  • An alpha particle
  • A beta particle
  • A gamma ray
  • A neutron
25
Q

What are the characteristics of an alpha particle?

A

An alpha particle(a) - This consists of two neutrons and two protons(like a helium nucleus)

They don’t penetrate very far into materials and are stopped quickly - they can only travel a few cm in air and are absorbed by a sheet of paper

26
Q

What are the characteristics of an beta particle?

A
  • A beta particle (B) is simply a fast-moving electron released by the nucleus
  • Beta particles have virtually no mass and a charge of -1
  • They are moderately ionising. They penetrate moderately far into materials before colliding and have a range in air of a few metres
    They are absorbed by a sheet of aluminium (around 5 mm)
  • For every beta particle emitted, a neutron in the nucleus has turned into a proton
27
Q

What are the characteristics of a gamma ray?

A
  • Gamma rays (y) are waves of electromagnetic radiation released by the nucleus
  • They penetrate far into materials without being stopped and will travel a long distance through air
  • This means they are weakly ionising because they tend to pass through rather than collide with atoms. Eventually they hit something and do damage
  • They can be absorbed by thick sheets of lead or metres of concrete
28
Q

What is radiation used for in todays society?

A

Today, to benefit humankind, radiation is used in medicine, academics, and industry, as well as for generating electricity. In addition, radiation has useful applications in such areas as agriculture, archaeology (carbon dating), space exploration, law enforcement, geology (including mining), and many others

29
Q

Note:

A

Check page 197 and see how nuclear equations work

30
Q

What does the emission of different types of nuclear radiation cause?

A

A change in mass or a change of the nucleus

31
Q

What does alpha decay cause?

A

Both the mass and charge of the nucleus to decrease

32
Q

What does beta decau cause?

A

Beta decay does not cause the mass of the nucleus to change but does cause the charge of the nucleus to increase

33
Q

What does gamma ray cause?

A

Gamme ray does not cause the mass or the charge of the nucleus to change

34
Q

Note:

A

Students should be able to use the names and symbols of common nuclei and particles to write balanced equations that show single alpha (a) and beta (B) decay. This is limited to balancing the atomic numbers and mass numbers. The identification of daughter elements from such decays is not required.

35
Q

Is radioactive decay fixed or random?

A
  • Radioactive decay is entirely random
  • So you can’t predict exactly which nucleus in a sample will decay next, or when any one of them will decay
36
Q

What is half-life of a radioactive isotope?

A

You can find out the time it takes for the amount of radiation emitted by a source to halve. It can be used to make predictions about radioactive sources, even though their decays are random.

Half-life can be used to find the rate at which a source decays - its ACTIVITY.
Activity is measured in becquerels, Bq (where 1 Bq is I decay per second)

37
Q

Concept of half-life

A
  • Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.
  • Count-rate is the number of decays recorded each second by a detector, such as the Geiger-Muller tube
38
Q

Note:

A

Hey, AQA says that student should be able to determine the half life of a radioactive isotopes given information

The initial activity of a sample is 640 Bq. Calculate the final activity as a percentage of the initial activity after two half-lives.

1) Find the activity after each half-life.
2) Now divide the final activity by the initial activity, 2 half-lives: 320 ÷ 2 = 160 then multiply by 100 to make it a percentage,ratio or decimal depending on what the question asks for

39
Q

Note:

A

AQA says students should be able to calculate the net secline expressed as a ratio in radioactive admission after a given number of half lives

40
Q

What is radioactive contamination?

A
  • Radioactive contamination is the unwanted presence of materials containing radioactive atoms of other materials
  • The Hazard from contamination is due to the decay of the contaminating atoms
  • The type of radiation emitted affects the level of the hazard
41
Q

What is irradation?

A
  • Irritation is the process of exposing an object of nuclear radiation
  • The irritated object does not become radioactive
42
Q

State the hazards associated with contamination

A
  • Radioactive isotopes may not go where they are wanted
  • It can be difficult to ensure that the contamination is fully removed so small amounts of radioisotope may still be left behind
  • Exposure to radioactive materials can potentially damage healthy cells
43
Q

State the hazards associated with irridation

A
  • it may not kill all bacteria on an object
    it can be very harmful
  • standing in the environment where objects are being treated by irradiation could expose people’s cells to damage and mutation
44
Q

What is the most dangerous radiation outside the body?

A
  • Beta and gamma sources, This is because beta and gamma can penetrate the body and get to the delicate organs
  • Alpha is less dangerous because it can’t penetrate the skin and is easily blocked by a small air gap
45
Q

What is the most dangerous radiation inside the body?

A
  • Alpha sources, because they do all their damage in a very localised area
  • So contamination, rather than irradiation, is the major concern when working with alpha sources
  • Beta sources are less damaging inside the body, as radiation is absorbed over a wider area, and some passes out of the body altogether
  • Gamma sources are the least dangerous inside the body, as they mostly pass straight out - they have the lowest ionising power
46
Q

What precautions must be taken to protect against any hazard that the radiactive source used in the process of irridation may present

A
  • Keeping radioactive sources shielded when not in use, for example in a lead-lined box
  • Wearing protective clothing to prevent the body becoming contaminated
  • Limiting exposure time so less time is spent with radioactive materials
  • Handling radioactive materials with tongs to increase the distance from them
  • Monitoring exposure using detector badges
47
Q

Note:

A

AQA says It is important for the findings of studies into effects of radiation on humans to be published and checked with other side, so that the findings can be checked by peer review

Science Spec Flaschcards (24 decks)

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