Radioactive decay - waves and particles Study Guide

Radioactive decay is a natural process where unstable atomic nuclei spontaneously transform into more stable forms by emitting particles and/or energy. This process is represented by nuclear equations, which must be balanced to reflect the conservation of mass number (total number of protons and neutrons) and atomic number (total number of protons). The mass number is written as a superscript before the element symbol, and the atomic number as a subscript. The particles commonly involved in radioactive decay are alpha particles, beta particles, and gamma rays. An alpha particle (α) is identical to a helium nucleus, represented as He. When an alpha particle is emitted, the mass number of the parent nucleus decreases by 4, and the atomic number decreases by 2. A beta particle (β) is an electron, represented as
e. Beta decay occurs when a neutron in the nucleus changes into a proton, emitting an electron and an antineutrino. This means the mass number remains unchanged, but the atomic number increases by 1. Gamma rays (γ) are high-energy electromagnetic radiation and carry no mass or charge, so their emission does not change the mass number or atomic number of the nucleus; they are often emitted alongside alpha or beta decay. When writing these equations, ensure that the sum of the mass numbers on the reactant side equals the sum of the mass numbers on the product side, and similarly for the atomic numbers. This rigorous balancing allows us to identify unknown particles or resulting nuclei in a decay series.

Every atom consists of a central nucleus surrounded by electrons. These electrons are not randomly scattered; instead, they occupy specific energy levels or shells at varying distances from the nucleus. Electrons closer to the nucleus have lower energy, while those further away have higher energy. The arrangement of these electrons is unique for each element and determines its chemical properties. This arrangement is dynamic and can change. When an atom absorbs electromagnetic radiation (like light or X-rays), an electron can gain enough energy to jump to a higher energy level further from the nucleus. This is an excited state, which is unstable. Conversely, when an electron falls from a higher energy level to a lower one, it emits a photon of electromagnetic radiation, losing energy in the process. The energy of the emitted photon corresponds to the difference in energy between the two levels.

Atoms are electrically neutral because they have an equal number of positively charged protons in the nucleus and negatively charged electrons. However, an atom can lose one or more of its outermost electrons. When this happens, the balance of charge is disrupted, and the atom becomes a charged particle called an ion. Specifically, if an atom loses electrons, it will have more protons than electrons, resulting in a net positive charge, and it is called a positive ion or cation. The removal of electrons requires energy, known as ionisation energy. This process is crucial in many physical and chemical phenomena, including the formation of ionic bonds and the operation of certain detectors in nuclear physics. Understanding these processes helps explain how matter interacts with energy and how elements behave.