WJEC Chemistry for AS: Study and Rev Guide

α particles – cluster of 2 protons and 2 neutrons, therefore positively charged. β particles – fast moving electrons, therefore negatively charged. γ rays – high energy electromagnetic radiation, therefore no charge. Key Terms Grade boost β particles can be considered as being formed when a neutron changes into a proton i.e. 1 0 n → 1 1 p + –1 β QUICKFIRE  Why are victims of radioactive contamination buried in lead coffins? QUICKFIRE  Give the mass number and symbol of the isotope formed when 18 F decays by positron emission. Radioactivity Types of radioactive emission and their behaviour Radiation Nature Effect of electric field Effect of magnetic field Penetrating power α particles clusters of 2 protons and 2 neutrons attracted to negative plate deflected in certain direction least penetrating stopped by a piece of paper β particles electrons attracted to positive plate deflected in opposite direction stopped by a thin sheet of metal (e.g. 0.5 cm of aluminium) γ rays high energy electromagnetic radiation no effect no effect most penetrating may take more than 2 cm of lead to stop them Effect on mass number and atomic number α and β particle emissions result in the formation of a new nucleus with a new atomic number therefore the product is a different element. When an element emits an α particle its mass number decreases by 4 and its atomic number decreases by 2. 238 92 U → 234 90 Th + 4 2 α The product is two places to the left in the Periodic Table. When an element emits a β particle its mass number is unchanged and its atomic number increases by 1. 14 6 C → 14 7 N + –1 β The product is one place to the right in the Periodic Table. In the process of electron capture, the mass number is unchanged and the atomic number decreases by 1. 59 28 Ni + e – → 59 27 Co The product is one place to the left in the Periodic Table. In the process of positron emission, the mass number is unchanged and the atomic number decreases by 1. 12 6 C → 12 5 B + β + The product is one place to the left in the Periodic Table. Pointer A positron is a type of β particle. It has the same mass as an electron and a numerically equal but positive charge. 12 AS Chemistry: Study and Revision Guide