Atomic structure and radiation flashcards

Students must understand the structure of the atom, including the roles of protons, neutrons and electrons, and how the nuclear model developed through key experiments. The nucleus is tiny compared to the whole atom and contains almost all its mass. Atoms of the same element can have different numbers of neutrons, making them isotopes. Unstable nuclei release radiation spontaneously in a process called radioactive decay. The three main types of nuclear radiation are alpha, beta and gamma, each with different penetrating power and ionising ability. Students must understand half-life, background radiation, uses and hazards of radiation, and the processes of nuclear fission and fusion. Understanding how to balance nuclear equations and interpret decay series is also required.

1. Card 1

   What are the three particles found in an atom and where are they located?

   Protons and neutrons are in the nucleus at the centre. Electrons orbit the nucleus in shells. The nucleus is tiny compared to the overall size of the atom.

2. Card 2

   What is the mass number and atomic number of an atom?

   The atomic number is the number of protons. The mass number is the total number of protons plus neutrons. In a neutral atom, the number of electrons equals the number of protons.

3. Card 3

   What are isotopes?

   Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. They have identical chemical properties but different masses and may be radioactive.

4. Card 4

   What is alpha radiation and what are its properties?

   An alpha particle consists of 2 protons and 2 neutrons. It is strongly ionising, stopped by a few centimetres of air or a sheet of paper, and carries a charge of +2.

5. Card 5

   What is beta radiation and what are its properties?

   A beta particle is a fast-moving electron emitted from the nucleus when a neutron turns into a proton. It is moderately ionising and stopped by a few millimetres of aluminium.

6. Card 6

   What is gamma radiation and what are its properties?

   Gamma radiation is a high-frequency electromagnetic wave emitted from an unstable nucleus. It is weakly ionising, very penetrating, and reduced significantly only by thick lead or concrete.

7. Card 7

   What is half-life?

   Half-life is the average time it takes for half the radioactive nuclei in a sample to decay. After each half-life the count rate and number of unstable nuclei both halve.

8. Card 8

   What was the Geiger-Marsden experiment and what did it show?

   Alpha particles were fired at gold foil. Most passed straight through, but some were deflected and a few bounced back, showing atoms have a tiny, dense, positively charged nucleus.

9. Card 9

   What is background radiation and give two natural sources?

   Background radiation is low-level radiation always present in the environment. Natural sources include radon gas from rocks and cosmic rays from space.

10. Card 10

    What happens to the nucleus during alpha decay?

    The nucleus loses 2 protons and 2 neutrons, so the mass number decreases by 4 and the atomic number decreases by 2, forming a different element.

11. Card 11

    What is nuclear fission?

    Nuclear fission is the splitting of a large, unstable nucleus (such as uranium-235) into two smaller nuclei, releasing energy and two or three neutrons that can trigger a chain reaction.

12. Card 12

    What is nuclear fusion and why is it difficult to achieve on Earth?

    Nuclear fusion is the joining of two light nuclei to form a heavier nucleus, releasing large amounts of energy. It requires extremely high temperatures and pressures, making it hard to sustain.

• Many students confuse mass number with atomic number, forgetting that mass number is the total of protons plus neutrons, not just the protons.
• Students often think that after one half-life all the radioactive material has gone, rather than understanding that only half the remaining unstable nuclei decay each half-life.
• A common error is stating that beta decay releases an electron that was already orbiting the nucleus, when in fact the electron is created when a neutron converts into a proton inside the nucleus.

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