Vertical trends

The 3d orbitals' smaller size compared with 4d and 5d has some significant consequences.

1. Electron repulsion is large among electrons in 3d orbitals. Exchange energy influence is more important; also, successive ionization energies (IEs) increase more sharply compared with later series.
2. 3d orbitals are not very much larger than the 3p orbitals of the argon core (3p)⁶. Good overlap with another atom is tough to achieve and covalent or metallic bonding including 3d orbitals is weak compared with 4d and 5d.

One result of the IE trend is that the higher oxidation states are less stable (more strongly oxidizing) as compared with the 4d and 5d series. For instance, in group 7 MnO₄^-is much more strongly oxidizing as compared with ReO₄^-and in group 8 FeO₄ is unknown even though RuO₄ and OsO₄ are stable compounds.

The bond-strength trend 3d<<4d<5d is the opposite of that generally found in main groups. Its affect can be observe in the atomization enthalpies of the elements, reflecting the strength of bonding within the metallic state, and displayed in Fig. 1 for elements of the three series. The extremely high atomization energies of elements like tungsten (5d group 6) are reflected in their very high melting and boiling points, a property significant in applications like electric light bulb filaments. Sublimation energies in the middle of 3d series are much less, partly due to the comparatively poor overlap of 3d orbitals provides weaker bonding, and partly due to the exchange energy stabilization of the free atoms, that have various unpaired electrons (example six with Cr). Compounds with unpaired electrons in the d orbitals are also much common in the 3d series; those of the 4d series more frequently creating low spin configurations or containing d electrons involved in metal-metal bonds.

Among the 4d and 5d series the supposed decrease of IEs and increase of radius is counteracted through the increase of nuclear charge involved in filling the 4f shell before 5d. 5d elements in early groups are extremely similar to the subsequent 4d ones, even though this feature is less noticeable in later groups.