Metallic Behaviour

All the transition elements are metals -- there are no non-metallic or metalloid d-block elements. Like metals generally, they are good conductors of both heat and electricity; of all known elements, silver has the single highest electrical conductivity at room temperature. Unlike the soft, low-melting metals of group 1 and group 2, the transition metals (with the exception of the group-11 elements, copper, silver and gold, which are comparatively soft) are hard solids, a consequence of strong metallic bonding involving both s and d electrons.

Most transition elements crystallise in one of three classic close-packed or near-close-packed lattice arrangements characteristic of true metals: hexagonal close packed (HCP), cubic close packed / face centred cubic (FCC), or body centred cubic (BCC). Scanning across the 3d, 4d and 5d series (Figure 4.2), these three structure types account for the overwhelming majority of transition metals, with only a few exceptions such as lanthanum's double hexagonal close packed (DHCP) structure and mercury's unusual rhombohedral (RHO) structure at the very end of the 5d series (mercury is, famously, a liquid at room temperature, the only metal that is).

Melting point across a transition series follows a characteristic rise-then-fall pattern rather than a simple monotonic trend. Moving from left to right along the series, melting point first increases, because the growing number of unpaired d electrons becomes increasingly available for strong metallic (and partially covalent, d-orbital-overlap) bonding between neighbouring atoms. The melting point reaches a maximum around the middle of the series, then decreases again as the d electrons progressively pair up (rather than remaining unpaired and available for inter-atomic bonding) toward the end of the row. In the first (3d) series concretely: melting point rises from scandium (m.p. 1814 K) up to a maximum of 2183 K at vanadium, staying nearly as high (2180 K) at chromium, before falling away. Manganese in the 3d series (and technetium, the corresponding element in the 4d series) show anomalously LOW melting points relative to their neighbours, breaking the smooth trend. That the maximum melting point occurs near the middle of the series, close to where the d⁵ configuration is reached, indicates that a half-filled d⁵ configuration is especially favourable for strong interatomic (metallic) attraction, since it maximises …