Periodic Table

Question 1

Explain the difference in atomic radius between Cl- ion and Ca2+ ion (hint: isoelectronic)

Answer 1

Being isoelectronic, both species have the same number of electrons and experience the same shielding effect. Ca2+ ion has higher nuclear charge and its valence electrons are thus more strongly attracted to the nucleus. Hence, size of Ca2+ is smaller than Cl-

OR: Both species are isoelectronic, but Cl- is an anion with valence electrons being less attracted to the nucleus due to lower nuclear charge, hence size of Cl- is larger than Ca2+

Question 2

Compare size of Ca2+ ion vs Ca atom (cationic radius vs atomic radius)

Answer 2

Valence electrons are removed from Ca atom to form the cation. Ca2+ has less electrons and one less shell of electrons. valence electrons are thus less shielded and closer to the nucleus, resulting in smaller radius.