(d-Block)

(bcc = body centred cubic; hcp = hexagonal close packed; ccp = cubic close packed; X = a typical metal structure). Fig. . : Trends in melting points of transition elements The transition metals (with the exception of Zn, Cd and Hg) are very hard and have low volatility.

Their melting and boiling points are high. Fig. . depicts the melting points of transition metals belonging to d , d and d series.

The high melting points of these metals are attributed to the involvement of greater number of electrons from (n- ) d in addition to the n s electrons in the interatomic metallic bonding. In any row the melting points of these metals rise to a maximum at d except for anomalous values of Mn and Tc and fall regularly as the atomic number increases. They have high enthalpies of atomisation which are shown in Fig. .

. The maxima at about the middle of each series indicate that one unpaired electron per d orbital is particularly