nuclear chemistry

Nuclear Stability

• if more than 84 nucleons, nuclide will undergo radioactive decay

• for small nuclei, stable when (A-Z)/Z is !

• large nuclei, (A-Z)/Z is > 1 (1.2- 1.4)

alpha decay

loss of helium nucleus (2 protons and neutrons)

• heavier nuclei

beta (- decay)

loss of an electron

• common for medium sized nuclides

beta (+ decay)

loss of a positron (positively charged electron)

• common for medium sized nuclides

electron capture (beta decay)

gain of an electron

• common for medium sized nuclides

gamma decay

• loss of a high energy photon ( no change in atomic or mass number)

decay series

successive radioactive processes until a stable nucleus is achieved

• usually combination of alpha and beta decay

Radiation detection

• geiger counter - detects high level b-particles

• scintillation counter - more sensitive

half-life

time it takes for the concentration of a species to decrease to ½ of its original value

nuclear stability and energies

E = mc²

for small change in mass → change in energy

• change in mass represents how much energy is needed to break down a nucleus into its components (nucleons)

Binding energies for different nucleons

• MeV - mega electron volt

1. determine mass defect

2. compare mass of atom, and subtract corresponding number of electrons

3. change in mass will be the atomic mass of nucleus - combined mass of 2 protons and 2 neutrons

4. plug into E = mc² (nucleon: divide by nucleon)

nuclear fission

• artificial transmutation (not naturally occurring)

• releases tremendous amounts of energy

• initiated by magic bullet

• for every 1 neutron that is used, three neutrons are produced

  • each of these neutrons can then be used for another fission reactions

    • known as chain reaction

nuclear fusion

• occurs on the sun

requires extremely high temperatures