GCSE / Physics
Atomic Structure
Revise GCSE Physics atomic structure, including the structure of atoms, protons, neutrons and electrons, atomic and mass numbers, isotopes, development of the atomic model, radioactive decay, alpha, beta and gamma radiation, nuclear equations, half-life, contamination, irradiation, background radiation, uses and hazards of radiation, nuclear fission and nuclear fusion.
Atomic structure describes how atoms are made from a tiny positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons arranged at different energy levels.
Atoms are extremely small, with a typical radius of about m, while the nucleus is much smaller and contains almost all of the atom’s mass.
The atomic number is the number of protons in the nucleus, and it determines the identity of an element because all atoms of the same element have the same number of protons.
The mass number is the total number of protons and neutrons in an atom, so the number of neutrons can be found using .
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, meaning they have the same atomic number but different mass numbers.
In a neutral atom, the number of electrons equals the number of protons, while an atom becomes a positive ion if it loses one or more outer electrons.
The development of the atomic model changed as new evidence was discovered, moving from early ideas of indivisible atoms to the plum pudding model, then to the nuclear model and finally to the modern model with electrons in energy levels.
Rutherford’s alpha particle scattering experiment showed that most of the atom is empty space and that nearly all of its positive charge and mass are concentrated in a very small nucleus.
Some atomic nuclei are unstable and undergo radioactive decay, a random process in which the nucleus emits radiation to become more stable.
Radioactivity and radiation measurement use activity in becquerels, where Bq means one nuclear decay per second, while count rate is the number of detections recorded each second by a radiation detector.
Alpha radiation consists of two protons and two neutrons, beta radiation consists of a high-speed electron emitted from the nucleus, and gamma radiation is electromagnetic radiation released from the nucleus.
In nuclear equations, both mass number and atomic number must balance; alpha decay reduces mass number by 4 and atomic number by 2, beta decay leaves mass number unchanged but increases atomic number by 1, while gamma emission changes neither.
Half-life is the time taken for the number of undecayed radioactive nuclei, or the activity or count rate of a radioactive sample, to fall to half its original value.
Radioactive contamination occurs when radioactive material gets onto or inside an object, whereas irradiation means exposing an object to nuclear radiation without making the object itself radioactive.
Nuclear fission is the splitting of a large unstable nucleus into smaller nuclei with the release of energy and neutrons, while nuclear fusion joins two light nuclei to form a heavier nucleus and also releases energy.