Ques. 1AIPMT 2012 (Prelims)
Identify the wrong statement in the following.
- Amongst isoelectronic species, smaller the positive charge on the cation, smaller is the ionic radius.
- Amongst isoelectronic species, greater the negative charge on the anion, larger is the ionic radius.
- Atomic radius of the elements increases as one moves down the first group of the periodic table.
- Atomic radius of the elements decreases as one moves across from left to right in the 2nd period of the periodic table.
Answer
(1) Amongst isoelectronic species, smaller the positive charge on the cation, smaller is the ionic radius.
Solution
As per NCERT, among isoelectronic species, the cation with the greater positive charge will have a smaller radius because of the greater attraction of the electrons to the nucleus; the anion with the greater negative charge will have the larger radius.
⇒ Smaller the positive charge on the cation, larger (not smaller) is the ionic radius, e.g. Na+ > Mg2+ > Al3+.
∴ Statement (1) is wrong.
Statements (2), (3) and (4) are correct: atomic radius increases down a group (new shells are added) and decreases across a period (effective nuclear charge increases).
Answer: (1)