Bellringer Please turn in your lab notebook to the cabinet In your INB, explain Rutherford’s Gold Foil Experiment and the conclusions he drew from his findings

Ernest Rutherford’s Gold Foil Experiment - 1911 Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foil Particles that hit on the detecting screen (film) were recorded

Rutherford’s Findings Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions: The nucleus is small The nucleus is dense The nucleus is positively charged

Nuclear Chemistry The study of the structure of atomic nuclei and the changes they undergo.

As you may recall, isotopes are atoms of the same element that have different numbers of neutrons. Isotopes of atoms with unstable nuclei are called radioisotopes

Radioactive Isotopes Stable Isotopes -Atoms that do not release protons or neutrons from the nucleus and ARE NOT RADIOACTIVE. Unstable Isotopes - Atoms that spontaneously release protons and neutrons from its nucleus. These isotopes ARE RADIOACTIVE.

Nuclear Reactions Nuclear reactions are different from chemical reactions Chemical Reactions Mass is conserved (doesn’t change) Small energy changes No changes in the nuclei; involve ONLY valance electrons Nuclear Reactions Small changes in mass Huge energy changes protons, neutrons, electrons and gamma rays can be lost or gained

Types of Radiation The effect of an electric field on three types of radiation is shown. Positively charged alpha particles are deflected toward the negatively charged plate.

Figure 4.2: The penetrating power of radiation. © 2003 John Wiley and Sons Publishers Figure 4.2: The penetrating power of radiation.

Products of Natural Radioactivity Mass Particle* Symbol Charge Number Identity Alpha 4 a 2+ 4 Helium nucleus 2 Beta 0 b 1- 0 Electron -1 Gamma 0 g 0 0 Proton of light *Sometimes a stream of any of these types of particles is called a ray, as in gamma ray,

Figure 4.4: The components of α rays, β rays, and γ rays. © 2003 John Wiley and Sons Publishers Figure 4.4: The components of α rays, β rays, and γ rays.

Types of radioactive decay alpha particle emission loss of a helium nucleus.

Types of radioactive decay Beta decay: nuclear changes that accompany the emission of a beta particle (CONVERTS A NEUTRON INTO A PROTON)

b particle emission

particle emission Gamma rays are high-energy (short wavelength) electromagnetic radiation. They are denoted by the symbol. As you can see from the symbol, both the subscript and superscript are zero. Thus, 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.

Induced Nuclear Reactions Scientists can also force ( = induce) nuclear reactions by smashing nuclei with alpha, beta and gamma radiation to make the nuclei unstable or

BALANCING NUCLEAR EQUATIONS 1. The sums of mass numbers (left superscripts) on each side must be equal. 2. The sums of atomic numbers or nuclear charges (left subscripts) on each side of the equation must be equal. Examples: 238U 4He + 234Th 92 2 90 214Pb 0 b + 214Bi 82 -1 83

Balancing Nuclear Equations Complete the following nuclear equations: 1. 217At 213Bi + ? 2. 231Th 0b + ? -1 3. 208Tl 0b + ? 85 83 4He 2 90 231Pa 91 81 208Pb 82

Nuclear Reactions Two types: Fission = the splitting of nuclei Fusion = the joining of nuclei (they fuse together) Both reactions involve extremely large amounts of energy Albert Einstein’s equation E = mc2 illustrates the energy found in even small amounts of matter

Nuclear Fission: Is the splitting of one heavy nucleus into two or more smaller nuclei, as well as some sub-atomic particles and energy. A heavy nucleus is usually unstable, due to many positive protons pushing apart. When fission occurs: Energy is produced. More neutrons are given off.

Nuclear Fission Neutrons are used to make nuclei unstable crash a neutral neutron into a nucleus to release energy

Fission produces a chain reaction

The fusion of hydrogen nuclei Nuclear Fusion joining of two light nuclei into one heavier nucleus. In the core of the Sun, two hydrogen nuclei join under tremendous heat and pressure to form a helium nucleus. When the helium atom is formed, huge amounts of energy are released. The fusion of hydrogen nuclei

Scientists cannot yet find a safe, and manageable method to harness the energy of nuclear fusion. “cold fusion” would occur at temperatures and pressures that could be controlled (but we haven’t figured out how to get it to happen)

Applications Medicine Agriculture Energy Chemotherapy Power pacemakers Diagnostic tracers Agriculture Irradiate food Pesticide Energy Fission Fusion

Half-Life The time required for the number of nuclides (# of protons + # neutrons) to reach half the original Amount remaining of Radioactive Isotope: N = N0 (1/2)n N is remaining amount N0 is the initial amount n is number of half lives that have passed

Half-Life Practice Problems #9 - 10 on page 872

A cancer patient receiving radiation therapy. © 2003 John Wiley and Sons Publishers Courtesy Kelley Culpepper/Transparencies, Inc. A cancer patient receiving radiation therapy.

© 2003 John Wiley and Sons Publishers Courtesy Scott Camazine/Photo Researchers The world’s first atomic explosion, July 16, 1945 at Alamogordo, New Mexico.

© 2003 John Wiley and Sons Publishers Courtesy Shigeo Hayashi Remains of a building after the explosion of the uranium bomb at Hiroshima, August 6, 1945.

Cooling towers of a nuclear power plant. © 2003 John Wiley and Sons Publishers Courtesy David Bartruff/Corbis Images Cooling towers of a nuclear power plant.

© 2003 John Wiley and Sons Publishers Courtesy Sipa Press The nuclear power plant at Chernobyl, after the accident of April 16, 1986.

© 2003 John Wiley and Sons Publishers Courtesy Yucca Mountain Project Construction of a tunnel that will be used for burial of radioactive wastes deep within Yucca Mountain, Nevada.

Disposal of radioactive wastes by burial in a shallow pit. © 2003 John Wiley and Sons Publishers Courtesy Matthew Neal McVay/Stone/Getty Images Disposal of radioactive wastes by burial in a shallow pit.