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Changes in Matter • Matter can undergo three types of changes. – Physical Change – change in appearance but not identity. – Chemical Change – production of new substances with different properties – same elements just rearranged – usually involves valence electrons. – Nuclear Change – form different element from what you started. • Nuclear changes involve changes in the nucleus of an atom. Radioactivity • Radioactivity – spontaneous emission of rays or particles from certain elements. (like uranium) – also known as radioactive decay – rays and particles emitted from a radioactive source are called nuclear radiation • Radioactivity is an example of a nuclear reaction. – Purpose of radioactive decay is for an unstable nucleus to become stable. – Nuclear reactions begin with unstable isotopes known as radioisotopes. – Atoms become stable when changes occur in the nuclei. – These changes are always accompanied by the emission of large amounts of energy. – Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence of catalysts. – Nuclear reactions of given radioisotope cannot be slowed down, speeded up, or stopped. – Radioactive decay is a spontaneous process. – If the product of a nuclear reaction is unstable, it will decay again. – The process continues until unstable isotopes of one element are changed, or transformed, into stable isotopes of a different element. – These stable isotopes are not radioactive. – Nuclear radiation is emitted during radioactive decay. – There are three main types of nuclear radiation: alpha radiation, beta radiation, and gamma radiation. Types of Radiation Alpha Radiation – An alpha particle (α) is two protons and two neutrons bound together and is emitted from the nucleus during some kinds of radioactive decay. (also referred to a as a helium nucleus) – Alpha particles have a positive charge – In nuclear equations, an alpha particle is written as – Example: • When an atom loses an alpha particle, the atomic number of the product is lowered by two and the mass number decreases by four. • In balanced nuclear equations, the sum of the mass numbers on the right must equal the sum on the left. • This is also true for the atomic numbers. • Alpha particles are the least penetrating type of radiation . – Sheet of paper or the surface of your skin can stop them. Beta Radiation – A beta particle (β) is an electron emitted from the nucleus during some kinds of radioactive decay. – A beta particle is formed when a neutron breaks apart into a proton and an electron. – The proton remains in the nucleus while the electron is ejected. – The -1 refers to the charge of the electron and the 0 refers to the mass. (essentially zero) – Example: • When an atom loses a beta particle, the atomic number of the product is increased by one; however, the mass number remains the same. • Since a beta particle has less charge and much less mass than an alpha particle, beta particles are more penetrating than alpha particles. – Beta particles can pass through paper but are stopped by aluminum foil or thin pieces of wood. Gamma Radiation – Gamma rays () are high-energy waves emitted from a nucleus as it decays. – Gamma rays have no mass and no electrical charge. Therefore, gamma radiation does not alter the atomic number or mass number of an atom. – Nuclei often emit gamma rays along with alpha or beta particles. • Gamma rays are the most penetrating type of nuclear radiation. • Easily pass through paper, wood, and human body (extremely dangerous). • They can be stopped, although not completely, by several meters of concrete or several centimeters of lead. Nuclear Equations and Radioactive Decay • Radium-226 is a radioactive isotope that decays by releasing an alpha particle. Write a nuclear equation for the radioactive decay of radium-226. • Potassium-40 decays by releasing a beta particle. Write a nuclear equation that represents the radioactive decay of potassium-40. Balancing Nuclear Equations Nuclear Equations Sample Problem 1. Identify the product that balances the following nuclear reaction: Reflection • Fill in the following table on your page.