Nuclear Chemistry

ATOMIC REVIEW: Atomic number = # of protons # of neutrons = mass # - atomic # protons & neutrons are in the nucleus

ATOMIC REVIEW: isotopes have different # of neutrons there are 3 forms of isotope notation carbon-12 C 12 6 C

Nucleon = term for all protons & neutrons Strong nuclear force short-range force among nucleons –Increases with shorter distance –NOT the same as an electric force isotopes have different # of neutrons there are 3 forms of isotope notation ATOMIC STRUCTURE carbon-12 C 12 6 C

Stable vs. Unstable Stable nuclei no spontaneous changes Unstable nuclei spontaneously changes to become a nucleus of a different element

Transmutation Unstable nuclei are naturally “built wrong” and “fall apart” An unstable nucleus undergoes transmutation, changing from one element into another –the nucleus changes # of protons!

Why? Radioactivity of an atom depends on the ratio of neutrons (N) to protons (P) How is a nucleus held together?  STRONG NUCLEAR FORCE

Why? Think about it!... protons are all positively charged and want to repel each other Neutrons act as a “nuclear glue” – they increase the strong nuclear force but don’t repel because they have no charge

Band of Stability N/P ratio of stable nuclei Stable small atoms (atomic # less than 20) are near 1/1 ratio Stable large atoms are near 1.5/1 ratio Predict the stability of the following: carbon-12 hydrogen-3 mercury-200 uranium-238

Discovery –In the 1900’s only 3 radioactive elements were identified –Today, all elements after bismuth are radioactive –The larger they are, the more easily they “fall apart”

Radiation Types 1. Alpha (  ) particles 2. Beta (  ) particles 3. Gamma (  ) rays 4. Positron emission 5. Electron Capture (EC )... and more Nuclear reactions have BALANCED nuclear equations!!

 (alpha) Particle it is a helium nucleus symbol: He or  low energy – doesn’t penetrate foil decreases the # of protons never emitted with beta Po  Pb + He

 (beta) Particle it is an electron (from the nucleus) symbol: e or  higher energy - penetrates the skin increases # of protons never emitted with alpha 0 0 C  N + e

 (gamma) Ray high energy electromagnetic wave no mass and no charge higher energy – blocked only by thick lead or thick concrete used to treat cancer usually is emitted with alpha or beta U  He + Th + 2 

Positrons or Electron Capture Positron emission  e –decreases # of protons –(product side of equation) Electron Capture, EC  e (reactant side of equation) –decreases # of protons Neutron captured or emitted  n

Fission & Fusion Nuclear Fission – the splitting of a nucleus into fragments –Very large release of energy –Used in nuclear power plants Nuclear Fusion – the combining of atomic nuclei –Very large release of energy –Occurs in the core of the sun & other stars –Requires high temperatures (5 million K) –Atomic explosions initiate fusion, but can’t be controlled... and many more!

Fission & Fusion Nuclear Fusion – the combining of atomic nuclei –Very large release of energy –Occurs in the core of the sun & other stars –Requires high temperatures (5 million K) –Atomic explosions initiate fusion, but can’t be controlled... and many more!