Classification of Elements and Periodicity in Properties - 1 - JEE MCQ

Generally as we move from left to right in a period, there is regular decrease in atomic radii and in a group as the atomic number increases the atomic radii also increases. Thus the atomic radius of Sn should be less than lanthanides. La > Sn. But due to lanthanide contraction, in case of lanthanides there is a continuous decrease in size with increase in atomic number. Hence the atomic radius follow the given trend:

Ce > Sn > Yb > Lu. 

With increase in atomic number i.e. in moving down a group, the number of the principal shell increases and therefore, the size of the atom increases. But in case of f ­block elements there is a steady decrease in atomic size with increase in atomic number due to lanthanide contraction. As we move through the lanthanide series, 4f electrons are being added one at each step.

The mutual shielding effect of f electrons is very little. This is due to the shape of the f ­orbitals. The nuclear charge, however increases by one at each step. Hence, the inward pull experienced by the 4f electrons increases. This causes a reduction in the size of the entire 4fⁿ shell.

The electronic configurations are as follows;

V:(Ar)3d³4s²

Cr:(Ar)3d⁵4s¹

Mn:(Ar)3d⁵4s²

Fe:(Ar)3d⁶4s²

The second ionization of Cr means removal of electron from the stable configuration of 3d⁵.

The highest second ionization enthalpy is Cr

Hence a is the correct answer.

Isoelectronic species are those which have same number of electrons.

K⁺ = 19 – 1 = 18 ; Ca²⁺ = 20 – 2 = 18

Sc³+ = 21 – 3 = 18 ; Cl^– = 17 + 1 = 18

Thus all these ions have 18 electrons in them.

The Lanthanide Contraction is caused by a poor shielding effect of the 4f electrons. Gd because as atomic number increases, the atomic radius decreases. These electrons are do not shield good, causing a greater nuclear charge.

For isoelectronic species, as the z/e decreases, ionic radius increases
such as ionic radii ∝ 1/z.

(A) For more polarity electronegativity difference should be  more E.N. (P) ≈ E.N. (H)

N–H > As–H > Sb–H > P–H is the order, (B) and (C) more is the size is gaseous phase less is hydration thus less is

hydrated size ∴ more is ionic mobility.

(D) Lattice energy depends on charge of cation and anion and internuclear distance thus order

MgO > SrO > NaF