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NUCLEAR CHEMISTRY
RADIOACTIVITY
 Radioactive means the nuclei of an atom changes
spontaneously and emits energy
 Nucleons are particles in the nucleus: protons and neutrons
 Isotopes have the same number of protons but different
numbers of neutrons
NUCLEAR EQUATIONS
 Most nuclei are stable. Radionuclides are unstable and
spontaneously emit particles and/or electromagnetic
radiation
 U-238 is radioactive
o It emits alpha particles(Helium-4 particles)
 When a nucleus decomposes in this manner, we say it has
decayed
 In nuclear equations, the total number of nucleons is
conserved
o 92238U 90234 Th + 42 He
TYPES OF RADIOACTIVE DECAY
 3 Types
o Alpha radiation is the loss of a He particle
o Beta radiation is the loss of an electron
o Gamma radiation is the loss of a photon
 Nucleons can undergo 2 other types of decay
o Positron emission ( same mass as an electron but
positive charge)
o Electron capture ( nuleus captures an electron from
the electron cloud)
NUCLEAR STABILITY
 Nuclei undergo decay to achieve stability
 If an isotopes mass number is greater than its atomic
weight, i.e. Carbon-16, the nucleus will try to gain protons
and lose neutrons. This results in Beta decay
 If the mass number is less, i.e. Carbon-11, the nucleus will
try to lose protons and gain neutrons. This results in
positron emission or electron capture
ENERGY CHANGES
 Einstein showed mass and energy are proportional: E = mc2
 If a system loses mass, it loses energy( exothermic)
 If a system gains mass, it gains energy ( endothermic)
 Since c2 is a very large number, small mass changes create
large energy changes
NUCLEAR BINDING ENERGY
 The mass of a nucleus is less than the mass of its nucleons
 This is termed mass defect
 Nuclear binding energy is the energy required to separate a
nucleus into nucleons
 The binding energy is related to the mass defect, E = mc2
HALF-LIFE
 Radioactive decay is a first order process: rate = kN
 Each isotope has a characteristic half-life
 Half-life is not affected by temperature, pressure or
chemical composition
 Half lives range from seconds to millions of years