Chemistry · Periodic Classification Of Properties · NEET
Being in the d-block only means the last electron went into a d orbital. But the real definition of a transition element is stricter: the element must have a PARTLY filled d orbital either in its neutral atom OR in one of its common ions. Zn is [Ar]3d10 4s2. Its d orbital is already full (d10). When it forms its only common ion, Zn2+, it loses the two 4s electrons and stays 3d10, still full. So Zn never has a partly filled d orbital. The same is true for Cd (4d10 5s2 -> Cd2+ is 4d10) and Hg (5d10 6s2 -> Hg2+ is 5d10). Full d in both the atom and the ion means they fail the definition.
Look at the d orbital. Scandium (Z=21) is [Ar]3d1 4s2, so its ground-state atom already has a partly filled d orbital (3d1). That is enough to call it a transition element. Zinc (Z=30) is [Ar]3d10 4s2, a completely filled d orbital, and its common Zn2+ ion is also 3d10. Since neither the atom nor the ion has a partly filled d orbital, zinc is not a typical transition element. This exact Sc-vs-Zn comparison is a favourite NEET/NCERT question.
No, and this is the whole point. Typical transition elements show variable oxidation states, coloured ions, paramagnetism, and good catalytic activity BECAUSE they have partly filled d orbitals. Zn, Cd and Hg have full d10 orbitals, so: they show mainly one fixed oxidation state (+2), their common ions are white or colourless (not coloured), their common ions are diamagnetic (no unpaired electrons), and they are poor catalysts. They behave more like normal metals than like transition metals.
Metallic bonding strength in transition metals comes from electrons in the (n-1)d orbitals joining the ns electrons in bonding. In Zn, Cd and Hg the d orbitals are completely filled and stable, so those d electrons do NOT take part in metallic bonding. Only the two ns electrons bond. Weaker metallic bonding gives low melting and boiling points and high volatility. This is why mercury is a liquid at room temperature. NCERT lists Zn, Cd, Hg (and Mn) as exceptions to the high melting points of transition metals.
Yes, copper IS a transition element, and this trips many students. The rule says PARTLY filled d in the atom OR in a common ion. Copper's atom is [Ar]3d10 4s1, but its common Cu2+ ion is [Ar]3d9, which has a partly filled d orbital. Similarly silver forms Ag2+ (4d9) in some compounds. So Cu, Ag qualify. But Zn2+, Cd2+, Hg2+ are all d10, never d9, so Zn, Cd, Hg do not qualify. The ion is the deciding factor.
Which among the following electronic configurations belong to main group elements? A. [Ne]3s1 B. [Ar]3d3 4s2 C. [Kr]4d10 5s2 5p5 D. [Ar]3d10 4s1 E. [Rn]5f0 6d2 7s2
Try the real previous-year questions from this chapter — each with the answer and a full solution.
They lie in the d-block, but they are NOT typical (real) transition elements, because they do not have a partly filled d orbital in the atom or in the common +2 ion. Both are d10.
General outer configuration is (n-1)d10 ns2. The d orbitals are completely filled in the ground state and stay filled in the common M2+ ion, so no partly filled d orbital ever exists.
Sc atom is 3d1 (partly filled d, so transition). Zn atom is 3d10 and Zn2+ is also 3d10 (full d, so not a typical transition element).
No. Because their ions have no unpaired d electrons, Zn2+, Cd2+ and Hg2+ compounds are usually white or colourless and diamagnetic, unlike coloured transition-metal ions.
Its full, stable 5d10 electrons do not join the metallic bonding, so only the two 6s electrons bond. This weak metallic bonding gives a very low melting point, keeping Hg liquid.
