Question

Which of the following elements have the highest melting points?

• A. Metals of the 5d transition series
• B. All the d block transition metals have melting points that are close to each other
• C. Metals belonging the 3d transition series
• D. Metals of the 4d transition series

Answer 1

The correct option is A Metals of the 5d transition series

The transition metals (with the exception of Zn, Cd and Hg) are very hard,
have low volatility and exhibit high melting and boiling points. The high melting points can be explained by the extensive involvement of greater number of electrons from (n-1)d in addition to the ns electrons in the interatomic metallic
bonding.
In any row (3d 4d or the 5d series), the melting points of these metals peak near the middle (Cr, Mo and W respectively). One unpaired electron per d orbital particularly maximizes the interatomic interaction. As a rule of thumb, we can say that greater the number of valence electrons, stronger is the resultant bonding.
Another generalization is that the metals of the 4d and 5d transition series have greater enthalpies of atomization than their 3d counterparts. Hence, 5d elements have the highest melting and boiling points.