surrounded by negatively charged electrons. The radius of a nucleus is less than 1/10,000 of the radius of an atom. Most of the mass of an atom is concentrated in the nucleus. The electrons are arranged at different distances from the nucleus (different energy levels). The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) of by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level). Describe the composition of an atom and draw a fully labelled diagram of an atom showing protons and neutrons in the nucleus with electrons outside the nucleus. Give the charges of all particles within the atom. Calculate the size of an atom given the size of the nucleus and the scale of the nucleus compared to the atom. Describe how the concentration of mass of an atom is not uniform but concentrated on the nucleus of the atom. Describe how electrons are arranged within an atom. Describe and explain how electrons can be moved further away from the nucleus of the atom and how they lose energy to move closer to the nucleus. Explain how the wavelength of the electromagnetic wave emitted by an electron emission spectra are formed.
Atoms turn into positive ions if they lose one or more outer electron(s) Calculate the number of neutrons for a stated element given the number of protons and the mass number. Calculate the mass number for a particular element given the number of protons and neutrons in the atom. Rearrange the equation to find number of protons or number of neutrons and the mass number. Explain how isotopes of elements, all have the same number of protons but have a different number of neutrons. Define isotope. Describe an atom in terms of number of protons, neutrons and electrons when given the following representation . 4.4.1.3 Scientific models of the atom and how these models have changed. New experimental evidence may lead to a scientific model being changed or replaced. Before the discovery of the electron, atoms were 0.6 Why has the model of the atom changed since ancient Greek times? Describe and explain why scientific models are replaced. Model the alpha scattering experiment by flicking a 1p coin through stack of 2p coins. The 1p coin represents the alpha particle and the stack of 2p coins the gold Video clip YouTube: Video clip YouTube:
of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name ‘proton’ was given to these particles. Lastly, in 1932, the experimental work of James Chadwick provided the evidence to show the existence within the nucleus of the neutron. This was about 20 years after the nucleus became an accepted scientific idea. have changed since ancient Greek times. Find out about the origins of the words protons, neutrons and electrons. 4.4.2 Atoms and radiation Spec ref. Summary of the specification content Learning outcomes What most candidates should be able to do Suggested timing (hours) Opportunities to develop Scientific Communication skills Opportunities to develop and apply practical and enquiry skills Self/peer assessment opportunities and resources Reference to past questions that indicate success
4.4.2.1 The radioactive decay of an unstable element. Activity is measured in Becquerel (Bq). Some atomic nuclei are unstable. The nucleus gives out ionising radiation as it changes to become more stable. This is a random process called radioactive decay. Activity is the rate at which a source of unstable nuclei decays and is measured in Becquerel. 0.4 Why are some atoms radioactive? Where does the radiation come from? Describe radioactive decay as a process by which an unstable atom releases radiation. How does activity change with time? Research how nuclear radiation was discovered and who discovered it. State that the part of the atom, which releases the radiation, is the nucleus. Describe how the emission of radiation from a radioactive atom is a random process, but over time the amount of decay can be predicted. Investigate the random nature of radioactive decay by throwing dice or coins. Is it possible to predict which dice will land on a six (or coins on a head)? 4.4.2.1 The nature of different types of nuclear radiation. The nuclear radiation emitted may be: an alpha particle (α) – this consists of two neutrons and two protons, it is identical to a helium nucleus 0.4 Are all radioactive sources the same? Describe the composition of each type of radiation and where relevant, give the particle that the type of radiation is identical to, eg an alpha particle is a helium nucleus. Model alpha, beta, gamma and neutron decay using plasticine and/or stop frame animation. Models should show the atom before and after decay as well as the radiation emitted.
charge of the nucleus to increase. The emission of a gamma ray does not cause the mass or the charge of the nucleus to change. Describe in words how the nucleus of an atom changes when it undergoes alpha and beta decay. Describe how the charge of a nucleus changes as it undergoes alpha and beta decay. 4.4.2.3 The randomness of radioactive decay. Radioactive is random so it is not possible to predict which individual nucleus will decay next. But with a large enough number of nuclei it is possible to predict how many will decay in a certain amount of time. 0.5 How does the activity of a radioactive substance change with time? Can you predict, with accuracy, which atoms in a radioactive substance will decay first? Describe the process of radioactive decay as being a random event analogous to flipping lots of coins – not knowing which coins will fall on heads but knowing about half of them will on any given throw. Demonstrate the randomness of the decay of a radioactive substance by throwing six dice and getting a prediction of the number of dice that will land on a six. Alternatively, drop 20 coins and get students to predict the number that will land on a head. 4.4.2.3 Determination of half-life calculations and graphical methods. 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 from a sample containing the isotope to fall to half of its initial level. 0.6 Define the term half-life. Calculate the half-life of a radioactive source from a decay curve of the radioactive element. Calculate the mass of a radioactive substance remaining after a given time when given the half-life of the substance and the Investigate half-life by throwing a large number of Tillich bricks. Any that land on the side with the odd colour get removed and the number remaining is recorded. Plot a graph
Students should be able to calculate the net decline, expressed as a in a radioactive emission after a given number of half-lives. HT only. initial mass of the radioactive source. of the number of throws against number of cubes remaining. Determine the half-life of the cubes (the number of throws needed to get the number of cubes to reduce by half). This experiment can also be carried out using coins. Is it possible to predict which cubes or coins will land on a certain side? 4.4.2.4 How to handle radioactive sources safely to avoid contamination. Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard. 0.7 Describe how radioactive contamination can occur. If radiation is dangerous, why is it used in schools? How would a person become contaminated by radiation? Explain how the procedure followed by people dealing with radioactive sources reduces the risk of contamination. Compare precautions taken by a teacher handling radioactive sources with those used by, say, in a nuclear power station.
4.4.3.1 Background radiation and sources of it. Background radiation is around us all of the time. It 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. 0.5 Where does background radiation come from? Do we (humans) contribute towards background radiation? Describe sources of background radiation, both man-made and natural. Explain why the level of background radiation is not the same across the planet in terms of altitude, geology and location of nuclear power stations. Describe the effect of nuclear weapons and their testing on the level of background radiation. Pose question: Are people in some exposed to more background radiation than others? If so why? 4.4.3.1 How the amount of background radiation depends on where you live and the job you do. The level of background radiation and radiation dose may be affected by occupation and/ or location. Radiation dose in measured in Sieverts (Sv). 0.5 Evaluate the risks involved to certain groups of people based on their occupations and/or location when supplied with relevant data. Research to see if the number of cases of cancer diagnosed per head of population increases in areas with higher levels of background radiation. Why is it not possible to link all the cases of cancer with levels of background radiation? Pose question: Are we at risk from background radiation? Is this greater or less than other parts of the country and why? PDF
4.4.4 Nuclear fission and fusion (physics only) Spec ref. Summary of the specification content Learning outcomes What most candidates should be able to do Suggested timing (hours) Opportunities to develop Scientific Communication skills Opportunities to develop and apply practical and enquiry skills Self/peer assessment opportunities and resources Reference to past questions that indicate success 4.4.4.1 Nuclear fission. Nuclear fission is the splitting of a and unstable nucleus (eg uranium or plutonium). 0.2 What happens when you split the nucleus of an atom? Can splitting the nucleus of an atom be done at home? What type of radiation is emitted when the nucleus of an atom splits? Draw a diagram to illustrate the fission process. Describe what happens to the nucleus of an unstable atom when it undergoes fission. Model nuclear fission of a uranium nucleus. 4.4.4.1 Spontaneous fission and nuclear fission in power stations. Spontaneous fission is rare. Usually for fission to occur the unstable nucleus must first absorb a neutron. 0.2 Describe and explain how nuclear fission happens in a nuclear power station. State that the reason nuclear fission is used is that the uranium atom decays too slowly naturally. Pose question: with reference to the conditions needed in a nuclear power station for fission to occur, does that affect their attitude towards having more nuclear power stations in the UK?