- D-block elements: The elements whose valence electrons are filled in d-orbital are called d-block elements, d-block elements are also called transitional elements. For example: The elements of group III B, IV B, V B, VI B, VII B, VIII B, I B and II B.
- F-block elements: The elements whose valence electrons are filled in f-orbital are called f-block elements. For example: The elements of Lanthanides and Actinides.
- Valency: The total number of electrons either gained or lost by an atom during their stability is called valency. in a period, valency increases first and then decreases. But in a group, valency remains constant.