The ions O2$$-$$, F$$-$$, Na+, Mg2+ and Al3+ are isoelectronic. Their ionic radii show
A
a significant increase from O2$$-$$ to Al3+
B
a significant decrease from O2$$-$$ to Al3+
C
an increase from O2$$-$$ to F$$-$$ and then decrease from Na+ to Al3+
D
a decrease from O2$$-$$ to F$$-$$ and then increase from Na+ to Al3+.
Explanation
Amongst isoelectronic ions, ionic radii of anions is more than that of cations. Further size of the anion increases with increase in -ve charge and size of cation decreases with increase in +ve charge. Hence, the correct order is
O2- > F- > Na+ > Mg2+ > Al3+
2
AIPMT 2000
MCQ (Single Correct Answer)
Which statement is wrong ?
A
Bond energy of F2 > Cl2
B
Electronegativity of F > Cl
C
F is more oxidising than Cl
D
Electron affinity of Cl > F
Explanation
Bond energy generally decreases on moving
from top to bottom along a group. It happens due to fact
that size increases on moving down the group and
thus, the two nuclei are far apart and less capable
of holding the two atoms together.
But in case of F2 molecule due to more repulsion in between non-bonding electron pair (2p) of two fluorines (due to small size of F-atom) in comparison to non-bonding electron pair (3p) in chlorine, the bond energy of F2 is less than Cl2.
BE(F2) = 158.5 kJ/mole and
BE(Cl2)= 242.6 kJ/mole
Questions Asked from Periodic Table and Periodicity
On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Indicates No. of Questions
