Chemistry · Periodic Classification Of Properties · NEET
Write the full configuration, then look at the sub-shell that received the LAST (highest-energy) electron. If it is an s sub-shell, it is s-block. If p, it is p-block. If (n-1)d, it is d-block. If (n-2)f, it is f-block. Example: Na = [Ne]3s^1, last electron in 3s, so s-block. Cl = [Ne]3s^2 3p^5, last in 3p, so p-block. V = [Ar]3d^3 4s^2, the filling that defines it is the inner 3d, so d-block.
Copper is a d-block element. Cu = [Ar]3d^10 4s^1. Even though the configuration is written ending in 4s^1, copper sits in Group 11 in the middle of the table and its chemistry comes from the inner (n-1)d electrons. The block is decided by the (n-1)d orbitals being filled across the row, not by which orbital is written last. So Cu is d-block (a transition metal), NOT s-block.
s-block: ns^1 to ns^2 (Groups 1 and 2). p-block: ns^2 np^1 to ns^2 np^6 (Groups 13 to 18). d-block: (n-1)d^1-10 ns^0-2 (Groups 3 to 12). f-block: (n-2)f^1-14 (n-1)d^0-1 ns^2 (the lanthanoids and actinoids at the bottom). Learn these four patterns and you can place almost any element.
They lie BETWEEN the s-block (very metallic) and the p-block (more non-metallic), so they form a transition or bridge in properties. In them the inner (n-1)d orbitals are being filled. They are all metals, often form coloured ions and show variable oxidation states. NCERT calls Group 3 to 12 the d-block or transition elements.
The f-block is the two rows placed separately at the bottom: Lanthanoids (Ce, Z=58 to Lu, Z=71) and Actinoids (Th, Z=90 to Lr, Z=103). Their last electron enters the inner (n-2)f orbital, so they are called inner-transition elements. They are drawn below the main table only to keep the table compact; chemically they belong in period 6 and period 7 of Group 3.
s-block = 2 groups (1 and 2). p-block = 6 groups (13 to 18). d-block = 10 groups (3 to 12). f-block = 14 columns (the inner-transition rows). This matches the orbital capacity: s holds 2 electrons, p holds 6, d holds 10, f holds 14. That is why block width equals orbital capacity.
By electron configuration helium is 1s^2, so it looks like an s-block element. But because it is a noble gas with a fully filled valence shell and behaves like Group 18, it is placed in the p-block (noble gases) in the periodic table. This is a special exception NCERT points out, and NEET can test it.
Which among the following electronic configurations belong to main group elements? A. [Ne]3s^1 B. [Ar]3d^3 4s^2 C. [Kr]4d^10 5s^2 5p^5 D. [Ar]3d^10 4s^1 E. [Rn]5f^0 6d^2 7s^2
It is because of inability of ns^2 electrons of the valence shell to participate in bonding that:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The type of atomic orbital that receives the last (highest-energy) electron. s, p, d or f sub-shell being filled gives the s-, p-, d- or f-block. This is the single rule to remember.
Main group elements are the s-block plus the p-block (Groups 1, 2 and 13 to 18). Transition elements are the d-block (Groups 3 to 12), where inner (n-1)d orbitals fill. See the next concept for a full comparison.
Yes. NCERT states all d-block (transition) and all f-block (inner-transition) elements are metals. They often show variable oxidation states and coloured ions.
Only to keep the table narrow and readable. The lanthanoids and actinoids really belong in Group 3 of periods 6 and 7, but placing 14 extra columns inline would make the table too wide.
Often yes. s-block = reactive metals, low ionization enthalpy, ionic compounds. p-block = both metals and non-metals, includes noble gases. d-block = transition metals, coloured ions, variable valency. f-block = inner-transition metals. Knowing the block is a fast first step in most periodicity questions.
