Term
| 7.1.1 Describe a model of the atom that features a small nucleus surrounded by electrons. |
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Definition
Students should be able to describe a simple model
involving electrons kept in orbit around the nucleus
as a result of the electrostatic attraction between
the electrons and the nucleus. |
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Term
| 7.1.2 Outline evidence that supports a nuclear model of the atom. |
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Definition
An outline and interpretation of the Geiger-Marsden experiment.
- alpha particles were fired at thin gold foil
- against expectations, the particles didn't pass through or rebound back, but most spread out. |
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Term
| 7.1.3 Outline one limitation of the simple model of the nuclear atom. |
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Definition
The problem with this theory was that accelerating charges are known to lose energy. If the orbiting
electrons were to lose energy they would spiral into the nucleus. The Rutherford model cannot explain
to us how atoms are stable. |
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Term
| 7.1.4 Outline evidence for the existence of atomic energy levels. |
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Definition
| When the electrons moved from a high energy state to a lower energy state they emitted a photon of light. The frequency of the light depends on the difference between the energy levels. As there are a fixed number of energy levels only a few wavelengths of light are given out. This results in a line spectrum. Each individual element has distinct energy levels and therefore the emission spectra can be used to identify them. |
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Term
| 7.1.5 Explain the terms nuclide, isotope and nucleon. |
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Definition
Nuclide – protons and neutrons that form a nucleus
Isotope – nuclei that have the same number of protons but a different number of neutrons.
Nucleon – The collective name for particles that are found in the nucleus (protons and Neutrons) |
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Term
| 7.1.6 Define nucleon number A, proton number Z and neutron number N. |
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Definition
Nucleon Number, A – The number of protons and neutrons that are in the nucleus.
Proton Number, Z – The number of protons that are in the nucleus.
Neutron Number, N – The number of neutrons that are in the nucleus. |
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Term
| 7.1.7 Describe the interactions in a nucleus. |
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Definition
- According to our knowledge, a nucleus should not be stable. The protons in the nucleus are positive charges so should repel each other. There must be another force in the nucleus that overcomes the electrostatic repulsion and hold the nucleus together. This force is called the STRONG NUCLEAR FORCE.
- Strong nuclear forces must be very strong to overcome the electrostatic forces. They must also have a very small range as they are not observed outside of the nucleus. |
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Term
| 7.2.1 Describe the phenomenon of natural radioactive decay. |
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Definition
| The uninitiated process of decay of unstable atomic nuclei. |
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Term
7.2.2 Describe the properties of alpha (α) and beta (β) particles and gamma
(γ) radiation. |
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Definition
α - low penetrability, path length a few cm, in E and B fields behaves like a positive charge
β - medium penetrability, path length less than 1m, in E and B fields behaves like a negative charge
γ - high penetrability, path length effectively infinite, not deflected in E and B fields |
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Term
7.2.3 Describe the ionizing properties of alpha (α) and beta (β) particles and
gamma (γ) radiation. |
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Definition
| All are ionising. This means that wwhen they go through a substance, collisions occur which cause electrons to be removed from atoms. |
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Term
7.2.4 Outline the biological effects of
ionizing radiation. |
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Definition
Ionisations can occur in DNA or RNA, which can cause mutations or death.
Short term immediate consequences:
High dose
- can effect the central nervous system, leading to loss of coordination and death within days
Medium dose
- can damage stomach and intestine, leading to diarrhoea and possibly death within weeks
Low dose
- loss of hair, bleeding, diarrhoea
Long term:
- growth of malignant cancer cells |
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Term
7.2.5 Explain why some nuclei are stable
while others are unstable. |
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Definition
- relative numbers of protons and neutrons and the forces involved
- A low amount of neutrons per proton increases the electrostatic repulsion between the particles, which cannot be fixed with the strong nuclear force, as it's short range. |
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Term
7.2.6 State that radioactive decay is a
random and spontaneous process and that the rate of decay decreases
exponentially with time. |
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Definition
| Exponential decay need not be treated analytically. It is sufficient to know that any quantity that reduces to half its initial value in a constant time decays exponentially. The nature of the decay is independent of the initial amount. |
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Term
| 7.2.7 Define the term radioactive half‑life. |
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Definition
| The time taken for half of an amount of radioactive material to decay. |
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Term
7.3.1 Describe and give an example of an
artificial (induced) transmutation. |
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Definition
Prompting nuclear reactions to happen by bombarding a nucleus with a nucleon, alpha particle or another small nucleus.
Typical nuclear fission reaction used in power plants:
235U + 1n -> 141Ba + 92Kr + 3*1n |
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Term
7.3.3 Define the term unified atomic mass
unit. |
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Definition
| One twelfth of the mass of a carbon-12 atom. |
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Term
7.3.5 Define the concepts of mass defect, binding energy and binding energy per
nucleon. |
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Definition
Binding energy: The amount of work required to pull apart the constituents of a nucleus.
mass defect: The difference between the mass of a nucleus and its parts. Results from energy transformations related to binding energy.
binding energy per nucleon: the ratio of binding energy to the amount of nucleons |
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Term
7.3.6 Draw and annotate a graph showing
the variation with nucleon number of
the binding energy per nucleon.
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Definition
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Term
7.3.8 Describe the processes of nuclear
fission and nuclear fusion. |
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Definition
Fission: A large nucleus is split into two smaller ones, which increases the binding energy per nucleon.
fusion: joining up two small nuclei to form a big one. this also increases the binding energy per nucleon. |
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Term
| 7.3.10 State that nuclear fusion is the main source of the Sun’s energy. |
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Definition
| Nuclear fusion is the main source of the Sun’s energy. |
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