Bohr's Classification Of Elements
Periodic Properties of Class 11
Elements may be classified into four groups on the basis of the number of incomplete shells present in them
- s- and p-orbitals of the outermost shell of these elements are filled. The outermost electronic configuration is ns2np6.
- Helium is also inert gas but its electronic configuration is 1s2
Representative or Normal Elements:
- The outermost shell of these elements is incomplete. The number of electrons in the outermost shell is less than eight.
- Inner shells are complete
- s-and p-block elements except inert gases are called normal or representative elements.
- The last two shells of these elements namely the outermost and penultimate shells are incomplete
- The last shell contains one or two electrons and the penultimate shell may contain more than eight up to eighteen electrons.
- Their outermost electronic configuration is similar to d-block elements i.e. (n-1)d1-10 ns1-2.
- According to the latest definition of transition elements, those elements which have partly filled d-orbitals in a neutral state or any stable oxidation state are called transition elements. According to this definition Zn, Cd, and Hg (IIB group) are d-block elements but not transition elements because these elements have d10 configuration in neutral as well as in stable +2 oxidation state.
Inner Transition Elements:
- In these elements last three shells i.e. last, penultimate, and pre-penultimate shells are incomplete.
- These are related to IIIB i.e. group 3.
- The last shell contains two electrons. The penultimate shell may contain eight or nine electrons and the pre-penultimate shell contains more than 18 upto32 electrons.
- Their outermost electronic configuration is similar to ƒ-block elements i.e. (n-2)ƒ1-14 (n-1)s2 (n-1)p6 (n-1)d0-1ns2
- Elements of the seventh period after atomic number 92 (i.e. actinides) are synthetic elements and are called transuranic elements.