Nuclear Chemistry

Isotopes-Review Isotopes are atoms of the same element that have the same # of protons but different # of neutrons or mass. X Atomic mass Atomic number

When the size and mass of the nucleus becomes large (greater than atomic #83), the element is known to be radioactive (unstable) because it decays. Examples: Pu-239 (94 protons), U-238 (92 protons) When the ratio of neutrons to protons is greater than 1:1 (for light nuclei) , the element is also radioactive. Carbon-14, Lithium-7

Natural radioactivity Occurs when nuclei are unstable. For any element, an isotope that is unstable is called a radioisotope.

Particles Emitted When a nucleus decays, it emits particles. Particle Mass Charge Symbol Penetrating Power Alpha 4 amu 2+ , 24He Low Beta 0 amu 1- -, -10e Moderate Positron 1+ + 10e  Gamma none , 00  High

Alpha Decay when an unstable nucleus emits an alpha particle, this is called alpha decay.

Beta Decay When an unstable nucleus emits a beta particle, this is called a beta decay.

Positron Emission When an unstable nucleus emits a positron, it is called positron emission

Writing Nuclear Equations Obeys laws of conservation of mass and charge. See Bb and worksheet for examples.

Natural Transmutation Begins with one nucleus that spontaneously decays. ***Always has ONE REACTANT.

Artificial Transmutation Bombardment of the nucleus with high energy particles. ***Always has TWO REACTANTS.

Fission Reactions Involve the splitting of a heavy nucleus to produce lighter nuclei. Fission reactions produce/capture neutrons. They can become involved in another fission reaction.

If the number of neutrons released is not controlled a chain reaction will occur. This is the type of reaction used in nuclear bombs.

Fusion Reactions Involves the combining of nuclei to produce heavier ones.

In fission and fusion reactions, there appears to be a loss of mass In fission and fusion reactions, there appears to be a loss of mass. However, this mass has been converted to energy by the equation E = mc2

Nuclear vs. Chemical Fission vs. Fusion The energy of nuclear reactions is much greater than the energy associated with chemical reactions. The energy of fission is greater than the energy of fusion.

Half-Life Radioactive substances decay at a rate that is not dependent on temperature, pressure, or concentration. Half-life is the time it takes for half the atoms in a given sample of an element to decay. See Table N for half-lives and modes.

Uses of Radioactivity Dating C-14 used to date organic remains; U-238:Pb-206 for minerals

Uses continued Chemical tracers can follow the path of a material (ex: fertilizer) Industrial applications can test thickness or strength of materials

Uses continued Medical applications must have short half-life and quickly eliminated from body, I-131 thyroid, Tc-99/Co-60 cancer

Dangers of Radioactivity Damage to tissue Gene mutation