As valence orbitals is called the orbital in the electron shell of atoms , with valence electrons are occupied. According to the modern atomic picture, chemical bonds are described by the interference of these valence orbitals.
The valence orbitals are the most energetic orbitals that are occupied with electrons in the ground state of the respective atom. Accordingly, they are furthest away from the core .
The valence orbitals of the main group elements include s and p orbitals of the outermost "shell". In the case of the subgroup elements (transition metals), the d orbitals of the second outermost shell are added to these, and in the case of the inner transition elements ( lanthanoids , actinides ) the f orbitals of the third outermost shell. (See also under electron configuration for a description of the orbital occupation)
The extent to which unoccupied d orbitals also influence the chemistry of the main group elements in the ground state is still a matter of controversy. In any case, they are not absolutely necessary to understand the binding relationships.