Activity - The rate at which a source of unstable nuclei decays. Measured in becquerel (Bq), Alpha particle - Made up of two protons and two neutrons (the same as a helium nucleus). Positively charged. Stopped by paper or skin. Has a range in air of a few cm. Highly ionising., Alpha scattering experiment - Observations from this experiment lead to the development of the nuclear model of the atom, Atomic number - The number of protons in an atom, Background radiation - Radiation around us all the time. It comes from natural and man-made sources, Beta particle - A fast moving electron from the nucleus. Negatively charged. Stopped by aluminum. Travels 1m in air., Contamination - The unwanted presence of radioactive atoms, Electron - Negatively charged particles which orbit the nucleus of an atom. Arranged in energy levels, Gamma ray - Electromagnetic radiation from the nucleus of an atom. No charge. Stopped by thick lead., Half-life - The time taken for the number of radioactive nuclei in a sample to halve, Ion - An atom which has lost or gained electrons and become charged, Irradiation - Process of exposing objects to radiatio. The object does not become radioactive , Isotopes - Isotopes of the same element have the same number of protons but different numbers of neutrons., Mass number - The number of protons and neutrons in the nucleus , Neutron - Particles found in the nucleus that have no electrical charge (they are neutral)., Nucleus - Positively charged, found at the centre of the atom. Contains protons and neutrons. Most of the mass of an atom is found here., Plum pudding model - This early model suggested that an atom was a ball of positive charge with electrons embedded in it, Proton - Positively charged particles found in the nucleus of an atom., Radioactive decay - A random process by which an unstable nucleus changes to become more stable.,

Year 9 Physics Atomic Structure Keywords

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