electron has moved towards the nucleus. 6.4.1.2 Describing an atom in terms of protons, neutrons and electrons. How to represent atoms. In an atom the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge. All atoms of a particular element have the same number of protons. The number of protons in an atom of an element is called its atomic number. The total number of protons and neutrons in an atom is called its mass number. Atoms of the same element can have different numbers of neutrons. These atoms are called isotopes of that element. Atoms can be represented as shown in this example: 0.5 What is ionisation? How can an atom be ionised? Why do some elements have isotopes? Describe the composition of a given atom in terms of the number of protons and electrons. Explain why atoms have no overall electrical charge, as the number of protons and electrons is equal. Research how atoms can be ionised by making the number of protons different to the number of electrons in an atom. State that the number of protons in a given element is always the same, though the mass number my change. Define the atomic number for an element. Calculate the number of neutrons for a stated element Use simple modelling techniques to show that the number of protons in an isotope of an element remains constant but the number of neutrons changes. Produce a table showing the mass number, atomic number and number of neutrons for an element given in the form . Pass My – Radioactivity, Atomic Structure, Atomic Number and Atomic Mass YouTube:
model’ of the atom. The ‘plum-pudding model’ suggested that the atom was a ball of positive charge with negative electrons embedded in it. The results from thealpha scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. The alpha scattering experiment led to the model’ being replaced by the nuclear model. Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the Draw a diagram to illustrate the ‘plum-pudding model’ of the atom. Explain why the ‘plum-pudding model’ was ‘better’ than the Greek model of the indivisible atom. Describe the alpha scattering experiment What was so amazing about the alpha scattering experiment? Details of these experiments are not required. Explain how the evidence from the scattering experiment led to a change in the atomic model of the atom. Describe the difference between the ‘plum-pudding model’ of the atom and the nuclear model of the atom. Produce a timeline to show how our ideas about atoms have changed since ancient Greek times. coins go straight through without scattering? What conclusion can be drawn about the arrangement of atomic nuclei in a material and the amount of free space between nuclei?
Activity is measured in Becquerel (Bq). 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. 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. to predict which dice will land on a six (or coins on a head)? 6.4.2.1 The nature of different of nuclear radiation. The nuclear radiation emitted may be: an particle (α) – this consists of two neutrons and two protons, it is identical to a helium nucleus a beta particle (β) – a high electron ejected from the nucleus as a neutron turns into a proton 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. Research how with beta decay an electron happens to be in the 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.
a gamma ray (γ) – electromagnetic radiation from the nucleus. a neutron (n) Describe how in beta emission a neutron decays into a proton and an electron, with the electron then being ejected from the nucleus at high speed. Describe gamma rays as being part of the electromagnetic spectrum as well as a type of nuclear radiation. Describe how a neutron can be emitted from a nucleus. 6.4.2.1 The penetration of alpha, beta and gamma radiation through different materials. Properties of alpha particles, beta particles and gamma rays limited to their penetration through materials and their range in air. 0.4 Which type of radiation is the most dangerous? Where do radioactive sources come from? Draw a diagram to illustrate the penetration of the different types of nuclear radiation. Evaluate the use of different shielding materials for use when handling radioactive sources when supplied with relevant data. Explain why gamma sources are usually the most harmful when outside the body and alpha are the most dangerous when inside the body in terms of penetration of the radiation. Demonstrate the penetration of alpha, beta and gamma radiation. Link the penetration of each type of radiation to the nature of the radiation and the uses of the radioactive sources. Plan an experiment to determine the type of radiation emitted by an unknown radioactive source. Produce a risk assessment for this experiment.
6.4.2.2 Nuclear decay equations Nuclear equations are used to represent radioactive decay. In a nuclear equation an alpha particle may be represented by the symbol: and a beta particle by the symbol: The emission of the different types of ionising radiation may cause a change in the mass and/or the charge of the nucleus. For example: Alpha decay causes both the mass and charge of the nucleus to decrease. Beta decay does not cause the mass of the nucleus to change, but it does cause the charge of the nucleus to increase. 0.5 How do atoms change when they undergo radioactive decay? Describe what happens to an atom when it undergoes beta and gamma emission. Calculate how the mass number, the proton number and the number of neutrons in an atom change when it undergoes alpha, beta and gamma emission. State the composition of alpha and beta particles and be able to recall that an alpha particle can be represented as: and a beta particle can be represented as: Complete nuclear decay calculations for alpha and beta decay. The calculations may be in the form of an equation or a table of results showing the same data. Describe in words how the nucleus of an atom changes when it undergoes alpha and beta decay. Model the radioactive decay of alpha and beta sources. Use the model to construct decay equations for alpha and beta decay. Critically analyse the limitations of the models produced by the class.