Question

Explain the following observation giving an appropriate reason for each.
The enthalpies of atomisation of transition elements are quite high.

Answer 1

The transition elements are considered as those elements which have partly filled d orbitals. It is considered as the element which has the partially filled d subshell with electrons or the element which has the tendency to form stable cations with the incompletely filled orbital of d. These transition elements in the modern periodic table are generally present from group 3 to group 12. Even the groups which consist of the lanthanides and the actinides are known as the transition elements.

Complete step-by-step answer: The energy of atomisation is defined as the change in the enthalpy or energy when one mole of the bonds are broken completely to obtain the atoms in the gaseous phase. For the molecules which are diatomic in nature their energy of atomisation usually equal to the enthalpy of bond dissociation.
The enthalpies of the atomisation of transition elements are generally quite high because as they have unpaired electrons due to which they tend to show strong metallic character, as they can easily lose an electron or two so that they could gain positive oxidation state which tends to make them more stable. Whereas the transition elements which do not unpaired electrons have less energy of atomisation because they have the tendency to break the metal metal bonds easily as these bonds will be weaker than the others.
The enthalpy of the atomisation is determined by the extent of the metallic bonding shown by the element. If the metallic character increases the energy of atomisation increases. In the transition metals the elements have some unpaired electrons with them which causes strong metallic bonding as they can lose their electrons to form metallic bonds and the interelectronic attractions are more which results in quite high enthalpy of atomisation.

Note: The transition element zinc does not have any unpaired electrons in it so it has least enthalpy of atomisation. As it does not have unpaired electrons so it cannot lose any electron to form metallic bonds. So it has low enthalpy of atomisation as the bonds present between the zinc atoms are weak as it requires lower energy to break them.