UNIT 15: NUCLEAR CHEMISTRY

Nuclear Radiation When Henri Becquerel placed uranium salts on a photographic plate and then developed the plate, he found a foggy image. The image was caused by rays that had not been observed before. For his discovery of radioactivity, Becquerel shared the 1903 Nobel Prize for Physics with Marie and Pierre Curie.

Radioactivity Radioactivity - the process by which materials spontaneously give off rays and particles Radiation - the penetrating rays and particles emitted by a radioactive source

Radioactivity In chemical reactions, atoms lose, gain or share electrons. In nuclear reactions, the nuclei of unstable isotopes, called radioisotopes, gain stability by undergoing changes. An unstable nucleus releases energy by emitting radiation during the process of radioactive decay.

Source of Nuclear Radiation Strong Nuclear Force stronger than electric repulsive force over very short distances. binds protons and neutrons together in the nucleus. + +

Source of Nuclear Radiation larger nucleus, more electric repulsion less stable (more radioactive) (Z > 83) Electric Force Electric Force Strong Nuclear Force Strong Nuclear Force

Types of Radiation The three main types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation. These three types of radiation deflect differently as they pass between a pair of electrically charged plates. Alpha particles (α) and beta particles (β) are deflected in opposite directions—alpha particles toward the negative plate and beta particles toward the positive plate. Gamma rays are undeflected. Applying Concepts Why are gamma rays not deflected?

Alpha Radiation Alpha radiation consists of helium nuclei, called alpha particles, that contain two protons and two neutrons and have a + 2 charge parent element daughter element Mass # - decreases by 4 Atomic # - decreases by 2

Radiation is emitted during radioactive decay Radiation is emitted during radioactive decay. a) Uranium-238 undergoes alpha decay to form thorium-234. b) Carbon-14 undergoes beta decay to form nitrogen-14. Interpreting Diagrams What particle is emitted in each decay process?

Beta Radiation An electron resulting from the breaking apart of a neutron in an atom is called a beta particle.

Beta Radiation Carbon-14 emits a beta particle as it undergoes radioactive decay to form nitrogen-14. parent element daughter element Mass # - stays the same Atomic # - increases by 1

Radiation is emitted during radioactive decay Radiation is emitted during radioactive decay. a) Uranium-238 undergoes alpha decay to form thorium-234. b) Carbon-14 undergoes beta decay to form nitrogen-14. Interpreting Diagrams What particle is emitted in each decay process?

Gamma Radiation A high-energy photon emitted by a radioisotope is called a gamma ray. The high-energy photons are electromagnetic radiation.

Types of Nuclear Radiation The penetrating power of nuclear radiation varies with the type.

Types of Nuclear Radiation The penetrating power of nuclear radiation varies with the type.

Types of Nuclear Radiation The penetrating power of nuclear radiation varies with the type.

Types of Nuclear Radiation The penetrating power of nuclear radiation varies with the type.

Types of Nuclear Radiation The penetrating power of nuclear radiation varies with the type.

Types of Nuclear Radiation The penetrating power of nuclear radiation varies with the type.

Types of Nuclear Radiation The penetrating power of nuclear radiation varies with the type. Alpha particles are the least penetrating. Gamma rays are the most penetrating.

Types of Radiation

Section Quiz. 1. Certain elements are radioactive because their atoms have more neutrons than electrons. an unstable nucleus. a large nucleus. more neutrons than protons.

Section Quiz. 2. An unstable nucleus releases energy by emitting radiation. thermal vibrations. a chemical reaction. giving off heat.

Section Quiz. 3. Which property does NOT describe an alpha particle? 2+ charge a relatively large mass a negative charge low penetrating power

Section Quiz. 4. When a radioactive nucleus releases a high- speed electron, the process can be described as oxidation. alpha emission. beta emission. gamma radiation.