11.1.3—Nucleon number and proton number
- Syllabus
- 9702–2028–2029
- Objective
- 11.1.3
- Level
- AS
Proton number identifies the element, while nucleon number counts protons plus neutrons
Proton number Z is the number of protons; nucleon number A is total protons plus neutrons, so neutron number is A−Z.
Z determines chemical identity. A can vary between isotopes while Z remains fixed.
A nuclide with A=23 and Z=11 contains 11 protons and 12 neutrons.
Nucleon number is not the number of electrons, and changing A alone does not create a new element.
ConceptA-Level CAIE Physics AS