Question
Define the terms:
(i) atomic number
(ii) mass number, of an atom in an element.
Solution
(i) The atomic number (z) is the number of protons present in the nucleus of an atom.
(ii) Mass number (A) is sum of the number of protons (p) and the number of neutrons (n) in the nucleus of an atom.
Thus, A = n + p or = n + z. (z is atomic number.) For example the mass of carbon is 12 u because it has 6 protons and 6 neutrons, 6 u + 6 u = 12 u
