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AH Physics > 4. Atomic Structure > Flashcards

4. Atomic Structure Flashcards

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1
Q

What is the radius of an atom?

A

The radius of an atom is about 1 × 10-10 metres

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2
Q

Describe the basic structure of an atom

A

The basic structure of an atom is a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons

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3
Q

Where is most of the mass of an atom concentrated?

A

Most of the mass of an atom is concentrated in the nucleus

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4
Q

Compare the radius of a nucleus to the radius of the atom

A

The radius of a nucleus is less than 1/10 000 (10,000 times smaller) of the radius of an atom

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5
Q

Describe the arrangement of electrons

A

Electrons are arranged at different distances from the nucleus (different energy levels)

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6
Q

Give 2 facts about energy levels

A
  • Each energy level is at a fixed distance from the nucleus
  • Energy levels that are further away from the nucleus are at a higher energy than those which are closer to the nucleus
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7
Q

Explain the 2 ways an atom’s electron arrangement can be changed

A

An atom’s electron arrangement can be changed through:
- Absorbing electromagnetic radiation - where electrons move further away from the nucleus to a higher energy level
- Emmitting electromagnetic radiation - where electrons move closer to the nucleus to a lower energy level

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8
Q

Describe and explain the overall charge of atoms

A

Atoms have no overall charge as the number of electrons is equal to the number of protons in the nucleus

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9
Q
A
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10
Q

What is the atomic number?

A

The atomic number is the number of protons in an atom

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11
Q

What is the mass number?

A

The mass number is the total number of protons and neutrons in an atom

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12
Q
A
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13
Q

What are isotopes?

A

Isotopes are atoms of the same element, which have the same number of protons but different number of neutrons, so they have different masses

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14
Q

How do atoms become positive ions?

A

Atoms become positive ions when they lose one or more of their outer electrons

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15
Q

What may lead to a scientific model being changed or replaced?

A

New expermental evidence that doesn’t agree with the existing theory

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16
Q

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

A

Before the discovery of the electron, Dalton thought that were atoms tiny spheres that could not be divided

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17
Q

What happened in 1897?

A

In 1897, J.J Thomson discovered the electron which led to his proposal of the plum pudding model

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18
Q

What did the plum pudding model suggest?

A

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

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19
Q

How was the plum pudding model disproved?

A

The plum pudding model was disproved by the results from Rutherford’s alpha particle scattering experiment

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20
Q

Describe what happened in the alpha particle scattering experiment?

A
  • A beam of alpha particles were aimed at a thin gold foil
  • Most of the alpha particles passed straight through the gold foil without changing direction
  • Some were slightly deflected but passed through the foil
  • Very few particles bounced back off the gold foil
21
Q

What were the results of the alpha particle scattering experiment?

A

Rutherford concluded that:
- Most of the atom consisted of empty space as most alpha particles went straight through the gold foil
- The nucleus must have a strong positive charge as some alpha particles were slightly deflected
- The mass of the atom must be concentrated at the centre as very few numbers of alpha particles rebounded by more than 90°

This became known as Rutherford’s nuclear model

22
Q

What did Niels Bohr do?

A

Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances

23
Q

Why was Bohr’s model accepted?

A

The theoretical calculations of Bohr agreed with experimental observations.

24
Q

What did James Chadwick do?

A

20 years after the nucleus became an accepted scientific
idea and the nuclear model, James Chadwick demonstrated the existence of neutrons

25
Q

Explain the process of radioactive decay

A
  • Some nuclei of atoms are unstable becaue they have too many or too few neutrons
  • The nucleus gives out radiation as it changes to become more stable
  • This is a random process
26
Q

What are the 4 ways nuclear radiation can be emitted?

A

Nuclear radiation can be emitted by:
- An Alpha particle (α)
- A Beta particle (β)
- A Gamma ray (γ)
- A neutron (n)

27
Q

Describe an alpha particle

A

An alpha particle consists of two neutrons and two protons, it is the same as a helium nucleus

28
Q

Describe a beta particle

A

A beta particle is a high speed electron ejected from the nucleus as a neutron turns into a proton

29
Q

What is a gamma ray?

A

A gamma ray is electromagnetic radiation from the nucleus

30
Q
A
31
Q

What is ionising power?

A

Ionising power is the ability of radiation to change an uncharged atom into a charged ion

32
Q

What is activity?

A

Activity is the rate at which a source of unstable nuclei decays

33
Q

What is activity measured in?

A

Activity is measured in becquerel (Bq)

34
Q

What is count rate?

A

Count-rate is the number of decays recorded each second by a
detector (eg Geiger-Muller tube)

35
Q

Complete it and state whether it is alpha or beta decay

A

Alpha decay

36
Q

Complete it and state whether it is alpha or beta decay

A
37
Q

What effect does alpha decay have on the mass and charge of the nucleus?

A

Alpha decay causes both the mass and charge of the nucleus to decrease

38
Q

What effect does beta decay have on the mass and charge of the nucleus?

A

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

39
Q

What effect do gamma rays have on the mass and charge of the nucleus?

A

The emission of a gamma ray does not cause the mass or the
charge of the nucleus to change

40
Q

What is half-life?

A

The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it
takes for the count rate (or activity) from a sample containing the
isotope to fall to half its initial level.

41
Q

Net decline

A

NOT SURE

42
Q

What is radioactive contamination?

A

Radioactive contamination is the unwanted presence of materials
containing radioactive atoms on other materials

43
Q

What is the hazard caused by radioactive contamination?
What is the level of the hazard caused by radioactive contamination?

A

The decay of radioactive atoms, which emit radiation
The level of danger / hazard is determined by the type of radiation emitted

44
Q

What is irradiation?

A

Irradiation is the process of exposing an object to nuclear radiation.
The irradiated object does not become radioactive

45
Q

What precautions should be taken to protect from alpha radiation

A

Gloves can protect against alpha radiation
Lead clothing can protect from beta and gamma radiation
Lead shielding can also be used

46
Q

Why it is important for the findings of studies into the effects of radiation on humans to be published and shared with other scientists?

A

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

47
Q

State one fact about background radiation

A

Background radiation is around us all of the time

48
Q

Where does background radiation come from?

A

Background radiation comes from:
- Natural sources such as rocks and cosmic rays from space
- Man-made sources such as the fallout from nuclear weapons
testing and nuclear accidents

49
Q

What factors affect the level of background radiation and radiation dose?

A

The level of background radiation and radiation dose may be
affected by occupation and/or location

AH Physics (11 decks)

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