Chemistry students often confuse the concepts of isotopes and ions. Consider the following three species:
1. Neutral potassium atom (K) with mass number 39
2. Potassium ion (K+) with mass number 39
3. Neutral argon atom (Ar) with mass number 40
The atomic numbers are ZK=19 and ZAr=18.
(a) For each of the three species listed, state the number of protons, neutrons, and electrons.
(b) Explain why species 1 and 2 are isotopes or are not isotopes of each other, and why each is or is not an ion.
(c) Despite having different atomic numbers, species 2 (K+) and species 3 (Ar) have the same number of electrons. Describe qualitatively how the heavier nuclear charge in potassium affects the allowed Bohr energy levels of those electrons compared with argon.