What are transition elements? Write two characteristics of transition elements.

Hint: Transition elements are a subset of d block elements. However not all d block elements are considered as transition elements. This is because of their electronic configuration. In order to understand transition elements, take an example of a transition element and a d block element and then compare their electronic configuration to explain their characteristics.

Complete step-by-step answer:
Transition elements or transition metals are elements that have partially filled d orbitals. IUPAC defines transition elements as an element having a d subshell that is partially filled with electrons that are able to form stable cations even with an incomplete d orbital.
All elements present in d block of the periodic table are transition elements except zinc, cadmium and mercury.
Elements present under the f block having incompletely filled orbitals are often referred to as inner transition elements or inner transition metals.
The characteristics of transition elements are :
- A large variety of ligands can bind themselves to the transition elements
- Compounds of transition elements have a characteristic colour due to electron transition in the degenerate orbitals.
- These elements have a large ratio of charge to radius
- Transition elements tend to be hard and they have relatively high densities when compared to elements of the same period.


Note: Zinc, cadmium and mercury are not considered as transition elements although they are part of the d block of the periodic table. This is because they have a completely filled d orbitals and do not have any unpaired electrons in any of their oxidation states.