1. Nuclear Chemistry Chapter 25

2. Nuclear Reactions Occur when nuclei emit particles and/or rays. Atoms are often converted into atoms of another element. May involve protons, neutrons, and electrons. Associated with large energy changes. Reaction rate is not normally affected by temperature, pressure, or catalysts.

3. Discovery of Radioactivity In 1895 Wilhelm Roentgen found that invisible rays were emitted when electrons bombarded the surface of certain materials. The emitted rays were discovered because they caused photographic plates to darken. Roentgen named these invisible high-energy emissions X rays.

4. Discovery of Radioactivity Marie Curie and her husband Pierre isolated the components of the emitted rays. Marie Curie named the process by which materials give off such rays radioactivity; the rays and particles emitted by a radioactive source are called radiation. In 1889, the Curies identified 2 new elements, polonium and radium, n the basis of their radioactivity.

5. Types of Radiation Isotopes are atoms of the same element that have different numbers of neutrons. Isotopes of atoms with unstable nuclei are called radioisotopes. – Radioisotopes- emit radiation to attain more stable atomic configurations in a process called radioactive decay. During radioactive decay, unstable atoms lose energy by emitting one of several types of radiation.

6. The Three Most Common Types of Radiation Alpha (α) Beta (β) Gamma (γ)

7. Alpha (α) Symbol: 4 He 2 The Alpha Particles carry a 2+ charge and are deflected toward the negatively charged plate. They are not very penetrating- single sheet of paper stops alpha particles. Has the same composition as a helium nucleus- two protons and two neutrons. Which is why it has the symbol above. Because Alpha particles consist of neutrons and protons they can only be emitted from the nucleus of an atom. Loss of an Alpha particle by a nucleus results in the formation of a new nucleus, lighter than the original by four mass units. An atom of the uranium isotope of mass 238, upon emitting an Alpha particle, becomes an atom of another element of mass 234. Each of the two protons that form part of the Alpha particle emitted from an atom of uranium-238 possesses a unit of positive electric charge. Because the charge on the uranium-238 nucleus decreases by two units as a result of Alpha emission, the atomic number of the newly formed atom is 2 fewer than that of the original, which was 92. The new atom has an atomic number of 90 and hence is an isotope of the element Thorium. Example:

8. Beta (β) Symbol: 0 β Beta particles carry a -1 charge and are deflected toward the positively charged plate Very fast moving electron that has been emitted from a neutron of an unstable nucleus. The Zero superscript in the symbol indicates the insignificant mass of an electron in comparison with the mass of a nucleus. The -1 Subscript denotes the negative charge of the particle. Example: Beta decay process is the decay of iodine- 131 into xenon- 131 by beta-particle emission The mass number of the product nucleus is the same as that of the original nucleus ( they are both 131), but its atomic number has increased by 1 (54 instead of 53). This changed in atomic number, and thus change in identity, occurs because the electron emitted during the beta decay has been removed from a neutron. Leaving behind proton. Have greater penetrating power than alpha particles. A thin metal foil is required to stop beta particles.

9. Gamma (γ) Symbol: 0 γ 0  Are high-energy electromagnetic radiation.  The emission of gamma rays does not change the atomic number or mass number of a nucleus.  Gamma rays almost always accompany alpha and beta radiation, as they account for most of the energy loss that occurs as a nucleus decays.  Example: gamma rays accompany the alpha-decay reaction of Uranium  Extremely penetrating and can be very damaging to living tissue.  Only partially blocked by lead and concrete.  Gamma rays are also used for diagnostic purposes in nuclear medicine. nuclear medicine  Example:

10. Types of Radioactive Decay Beta Decay- Note that the atomic number of the product nucleus has increased by 1. Alpha Decay- Note that the atomic number decreases by 2 and the mass number decreases by 4 Gamma Emission- Note that the atomic number and mass number do NOT change