Rapid Review
Know how nuclear equations are balanced: The same sums of both mass and atomic
numbers appear on both sides of the equation.
Know the five naturally occurring decay modes:- Alpha emission, in which a helium nucleus, , is emitted from the nucleus.
2. Beta emission in which an electron, − 10 e, is emitted from the nucleus. This is due to
the conversion of a neutron into a proton plus the beta particle.
3. Gamma emission, in which high-energy electromagnetic radiation is emitted from
the nucleus. This commonly accompanies the other types of radioactive decay. It is
due to the conversion of a small amount of matter into energy.
4. Positron emission, in which a positron, , a particle having the same mass as an
electron but a positive charge, is emitted from the nucleus. This is due to a proton
converting into a neutron and the positron. - Electron capture, in which an inner-shell electron is captured by a proton in the
nucleus with the formation of a neutron. X-rays are emitted as the electrons cascade
down to fill the vacancy in the lower energy level.
Know that nuclear stability is best related to the neutron-to-proton ratio (n/p), which
starts at about 1/1 for light isotopes and ends at about 1.5/1 for heavier isotopes with
atomic numbers up to 83. All isotopes of atomic number greater than 84 are unstable
and will commonly undergo alpha decay. Below atomic number 84, neutron-poor isotopes
will probably undergo positron emission or electron capture, while neutron-rich isotopes
will probably undergo beta emission.
Know that the half-life, t1/2, of a radioactive isotope is the amount of time it takes for
one-half of the sample to decay. Know how to use the appropriate equations to calculate
amounts of an isotope remaining at any given time, or use similar data to calculate the
half-life of an isotope.
Know how to use Einstein’s equation E= mc^2 to calculate the amount of energy
produced from a mass defect (the amount of matter that was converted into energy).
+ 1(^0) e
2
(^4) He
Nuclear Chemistry 267