NEETChemistryd and f Block Elements
Which of the following periodic trends among transition elements is a direct consequence of lanthanoid contraction?
Options
- AThe atomic radii of 4d series elements are significantly larger than those of the corresponding 3d series elem
- BThe melting points of transition metals reach a maximum near the middle of each series.
- CThe densities of 3d series elements are generally lower than those of the corresponding s-block elements.
- DThe first ionization enthalpies of 5d series elements are generally higher than those of the corresponding 3d
Correct answer
D. The first ionization enthalpies of 5d series elements are generally higher than those of the corresponding 3d
Step-by-step solution
The lanthanoid contraction results in the 5d series elements having atomic radii very similar to those of the corresponding 4d series elements. However, the nuclear charge of 5d elements is higher by 32 units. Because the 4f electrons provide poor shielding, the effective nuclear charge acting on the outer valence electrons in 5d elements is significantly greater. As a result, the first ionization enthalpies of 5d elements are generally higher than those of the corresponding 3d and 4d elements. Option 1 is true but