These points are from my teaching guidelines for the Preliminary Chemistry Course, on Module 1 Properties of Matter.
Students are not required to predict the stability of any particular nucleus.
Students are provided the graph of the band of stability of isotopes, showing atomic number A (number of protons) on the horizontal axis, and number of neutrons on the vertical axis.
Students recognise the following patterns in the graph:
- Stable isotopes of the light elements contain approximately a ratio of 1:1 protons and neutrons.
- As A increases, more neutrons than protons are required to maintain stability in the nucleus. The graph bends upwards.
- If a light nucleus contains substantially more protons than neutrons, it is likely to be unstable and emit Beta+ radiation to rid itself of the excess positive charge.
- If a light nucleus contains substantially more neutrons than protons, it is likely to be unstable and emit Beta- radiation to increase the number of protons and decrease the number of neutrons.
- At Z = 200 the proton : neutron ratio increases to 1:1.5 and beyond Z = 208 there are no stable isotopes.
- All nuclei beyond Z = 208 decay, usually by emission of alpha particles, because emission of an alpha particle will move the nucleus quickly towards the band of stability.