Chapter 4, section 4 Chapter 24 Nuclear Chemistry Chapter 4, section 4 Chapter 24

Atomic Structure Review Atomic # = # of Protons # of Neutrons = Mass # - Atomic # Isotopes have different #’s of neutrons Isotope notation: Carbon-12 = C Nucleon: General term for all protons & neutrons Strong Nuclear Force: Short-range force among nucleons Increases with shorter distance Not the same as an electric force 12 6

Discovery In the 1900’s, only 3 radioactive elements were identified Today, it is known that all elements after bismuth (83) are radioactive The larger the atoms are, the more easily they “fall apart”

Stable vs. Unstable Nuclei Nuclei can be stable or unstable Stable nuclei do not spontaneously change Unstable nuclei spontaneously change to become nuclei of different elements (the number of protons change)

Transmutation Unstable nuclei are naturally “built wrong” and “fall apart” The process by which one element becomes another is called transmutation -the nucleus’ number of protons is changed

Radioactivity (breaking down of nucleus) Radioactivity of an atom depends on the ratio of neutrons (n) to protons (p+) # n # p+

Band of Stability Which atoms are stable? A small atom (atomic # less than 20) is stable if its N/P ratio is very close to 1/1 A large atom (atomic # 20 or more) is stable if its N/P ratio is very close to 1.5/1 Predict the stability of the following: Carbon-12 Hydrogen-3 Mercury-200 Uranium-238

Types of Radiation https://www.youtube.com/watch?v=o-9yt7OAYmE (1min16sec) During radioactive decay, unstable atoms lose energy by emitting radiation The three most common types of radiation are alpha (α), beta (β) & gamma (γ)

alpha (α) particles Po  Pb + α The symbol for an alpha particle is α where 4 is the mass and 2 is the charge These particles are low in energy (they can’t even penetrate foil) If these particles are emitted from an atom, the number of protons decreases Alpha particles are never emitted with beta particles Example: 4 2 Po  Pb + α 210 84 206 82 4 2

beta (β) particles C  N + The symbol for a beta particle is β where 0 is the mass and -1 is the charge These particles are higher in energy than alpha particles (they can penetrate skin) If these particles are emitted from an atom, the number of protons increases Beta particles are never emitted with alpha particles Example: β -1 C  N + 14 6 7 -1

Gamma (γ) particles U  α + Th + 2  The symbol for a gamma particle is γ where 0 is the mass and 0 is the charge These particles are high energy electromag waves They have no mass or charge They have higher energy than beta particles- they are blocked only by thick lead or thick concrete They are used to treat cancer if used “properly” Usually emitted with alpha or beta particles Example: U  α + Th + 2  238 92 4 2 234 90

Positron or Electron Capture If positrons ( e) are emitted, the number of protons decreases (if something is emitted, it will be on the PRODUCT side of the equation) If electrons ( e) are captured, the number of protons also decreases (if something is captured, it will be on the REACTANT side of the equation) When a neutron is captured or emitted, use the symbol ( n) 1 -1 1

Fission and Fusion Nuclear Fission Nuclear Fusion The splitting of a large atom into smaller ones Does not normally occur in nature – Man-generated and used in nuclear in power plants Requires little energy Releases a lot of energy The fusing of lighter atoms into a larger one Occurs in stars (Ex: the sun) Requires a lot of energy Releases 3 to 4 times more energy than fission rxns