Nuclear Chemistry

Nuclear Reactions Nuclear chemistry is the study of changes in an atom’s nucleus. Nuclear chemistry is the study of changes in an atom’s nucleus. Reactions that involve a change in the nucleus of an atom are called nuclear reactions. Reactions that involve a change in the nucleus of an atom are called nuclear reactions.

Characteristics of Nuclear Reactions Occur when nuclei emit particles and/or rays Occur when nuclei emit particles and/or rays Atoms are often converted into atoms of another element Atoms are often converted into atoms of another element May involve protons, neutrons, and electrons May involve protons, neutrons, and electrons Associated with large energy changes Associated with large energy changes Reaction rates aren’t normally affected by temperature, pressure, or catalyst Reaction rates aren’t normally affected by temperature, pressure, or catalyst

What Causes Nuclear Reactions? The nuclei of some atoms are unstable and may undergo several changes. The nuclei of some atoms are unstable and may undergo several changes. Unstable systems gain stability by losing energy. Unstable systems gain stability by losing energy. Certain atoms lose energy by emitting rays and particles called radiation. Certain atoms lose energy by emitting rays and particles called radiation.

Related Terms This spontaneous emission of radiation is a process called radioactivity. This spontaneous emission of radiation is a process called radioactivity. The process by which unstable nuclei emit radiation to lose energy is called radioactive decay. The process by which unstable nuclei emit radiation to lose energy is called radioactive decay. Radioisotopes, isotopes of atoms with unstable nuclei, undergo nuclear decay. Radioisotopes, isotopes of atoms with unstable nuclei, undergo nuclear decay.

Types of Radiation Alpha Alpha -Composed of alpha particles -Contains 2p + and 2n ⁰ He or α Beta -Composed of beta particles -Fast moving e β or 0 -1 e

Types of Radiation (cont) Gamma Gamma -Not deflected by electric or magnetic fields -High energy electromagnetic radiation (not a particle) -No mass and No charge γ istry/essentialchemistry/flash/radioa 7.swf istry/essentialchemistry/flash/radioa 7.swf istry/essentialchemistry/flash/radioa 7.swf istry/essentialchemistry/flash/radioa 7.swf

Types of Radiation Summary Type of Radiation SymbolCharge Penetrati on AbilityMass alpha 4 2 He 2+ blocked by paper heaviest (4 amu) beta 0 -1 β 1- blocked by metal foil lightest (1/1840 amu) gamma 00γ00γ00γ00γ0 not completely blocked by lead or concrete none

Nuclear Equations Used to express nuclear reactions Used to express nuclear reactions Both sides of the equation must have an equal sum of atomic mass and atomic numbers Both sides of the equation must have an equal sum of atomic mass and atomic numbers Examples: Examples: U  4 2 He Th U  4 2 He Th K  0 -1 β Ca K  0 -1 β Ca Ca  Ca γ Ca  Ca γ

Half-Life The time required for one half of a radioisotope’s nuclei to decay into its products is called a half-life. The time required for one half of a radioisotope’s nuclei to decay into its products is called a half-life. Amt Remaining=(Initial Amt)(1/2) n Amt Remaining=(Initial Amt)(1/2) n -n = # half lives passed Amt Remaining=(Initial Amt)(1/2) t/T Amt Remaining=(Initial Amt)(1/2) t/T -t=elapsed time -T=duration of half life

Example half-life problems: Example half-life problems: - How much of a 100.0g sample of 198 Au is left after 8.10 days if its half- life is 2.70 days? -A 50.0g sample of 16 N decays to 12.5g in 14.4 seconds. What is its half-life? -The half-life of 42 K is 12.4hours. How much of a 750g sample is left after 62.0hours? -What is the half-life of 99Tc if a 500g sample decays to 62.5 g in 639,000 years?

Fission and Fusion The splitting of an atoms nucleus into fragments is called fission. The splitting of an atoms nucleus into fragments is called fission. -Provides energy for nuclear power plants h_viewer.php?oid=2391&mid=59 h_viewer.php?oid=2391&mid=59 h_viewer.php?oid=2391&mid=59 h_viewer.php?oid=2391&mid=59 The combining of atomic nuclei is called fusion. The combining of atomic nuclei is called fusion. -Fuels the sun h_viewer.php?oid=2747&mid=59 h_viewer.php?oid=2747&mid=59 h_viewer.php?oid=2747&mid=59 h_viewer.php?oid=2747&mid=59