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Zinc is in the d-block of the periodic table, its outer electrons are in 3d and 4s orbitals, and it sits at the end of the first transition series. Yet NCERT says it is not a transition element. This looks like a contradiction until you read the definition carefully. This post applies the definition to three metals, shows how one fact, a full d subshell, explains several of zinc's properties, and notes the research result on mercury that is sometimes raised in class.
Where is this in the syllabus?
The JEE (Main) 2026 syllabus and the NEET (UG) 2026 syllabus open Unit 11, d- and f-Block Elements, with "general introduction, electronic configuration, occurrence and characteristics" of transition elements, followed by trends in the first row including colour and magnetic properties. The JEE (Advanced) 2026 brochure covers d-block oxidation states and their stability. The NCERT Class 12 Chemistry Unit 4, The d- and f-Block Elements (2026-27 reprint), gives the definition and the data used below. Check your own year's syllabus.
What is the definition?
NCERT: "according to IUPAC, transition metals are defined as metals which have incomplete d subshell either in neutral atom or in their ions." It then adds: "Zinc, cadmium and mercury of group 12 have full d¹⁰ configuration in their ground state as well as in their common oxidation states and hence, are not regarded as transition metals." Later in the unit it gives the outer configuration of Zn, Cd, Hg and copernicium (Cn) as (n−1)d¹⁰ns², and notes that their chemistry is still studied with the transition metals because they end the 3d, 4d and 5d series.
So the test has two parts. Look at the atom. If its d subshell is full, look at its common ions too. Only if both are full is the element left out.
Worked example 1: apply the test to Sc, Cu and Zn
Use NCERT's Table 4.2 configurations.
Scandium. Atom 3d¹4s². The d subshell is incomplete in the atom, so scandium is a transition element. Its common ion, Sc³⁺, has no d electrons, but the atom alone is enough. This is NCERT's Example 4.1.
Copper. Atom 3d¹⁰4s¹, a full d subshell. Now check the ion: Cu²⁺ is 3d⁹. Incomplete, so copper is a transition element.
Zinc. Atom 3d¹⁰4s². Its only common ion, Zn²⁺, is 3d¹⁰. Full in both, so zinc is not a transition element.
Copper and zinc have the same full 3d¹⁰ in the atom. The difference is what happens when they form ions.
How does a full d subshell show up in zinc's properties?
Colour. NCERT's Table 4.8 lists aquated Zn²⁺ (3d¹⁰) as colourless, while Cu²⁺ (3d⁹) is blue. NCERT explains colour as an electron being excited from a lower to a higher energy d orbital, which needs a vacancy to move into.
Magnetism. NCERT's spin-only formula is μ = √(n(n + 2)) BM, where n is the number of unpaired electrons.
Cu²⁺, n = 1: μ = √3 = 1.73 BM. Paramagnetic.
Zn²⁺, n = 0: μ = 0. Diamagnetic.
Bonding in the metal. NCERT explains that transition metals have high enthalpies of atomisation because their many unpaired electrons give "stronger interatomic interaction". Its Table 4.2 lists 339 kJ mol⁻¹ for copper and 126 kJ mol⁻¹ for zinc, the lowest in the row; the unit's intext question 4.2 asks you why. With every 3d electron paired, zinc's metallic bonding relies on its 4s electrons. NCERT also notes that, with the exceptions of Zn, Cd and Hg, the transition metals are "very hard and have low volatility".
Oxidation states. NCERT says "the only oxidation state of zinc is +2 (no d electrons are involved)". Its Table 4.2 gives zinc's third ionisation enthalpy as 3837 kJ mol⁻¹, the highest of the row, because a third electron would have to come out of the stable 3d¹⁰ shell.
Worked example 2: a spot-the-odd-one question
Which of Sc³⁺, Ti³⁺, Cu²⁺ and Zn²⁺ are coloured and paramagnetic?
Configurations: Sc³⁺ 3d⁰, Ti³⁺ 3d¹, Cu²⁺ 3d⁹, Zn²⁺ 3d¹⁰.
Unpaired electrons: 0, 1, 1, 0.
Spin-only moments: 0, 1.73, 1.73 and 0 BM.
Ti³⁺ and Cu²⁺ are coloured and paramagnetic; Sc³⁺ and Zn²⁺ are colourless and diamagnetic. NCERT's Table 4.8 agrees: Sc³⁺ colourless, Ti³⁺ purple, Cu²⁺ blue, Zn²⁺ colourless. Note that scandium is still a transition element; the question is about ions, not elements.
What about mercury?
In 2007, Wang, Andrews, Riedel and Kaupp published a paper titled "Mercury is a transition metal: the first experimental evidence for HgF₄". In HgF₄ mercury would be +4, which is 5d⁸, a partly filled d subshell. That would meet the IUPAC test through an ion. It is not a common oxidation state, and it has not changed how NCERT or the exam syllabi classify group 12. For your exam, follow NCERT: Zn, Cd and Hg are not transition elements. Our post on transition metal oxidation states covers the rest of the row.
Which mistakes cost marks?
Saying zinc is a transition metal because it is in the d-block. Position is not the test.
Saying copper is not a transition metal because its atom is 3d¹⁰. Check Cu²⁺.
Writing Zn²⁺ as 3d⁸4s². The 4s electrons leave first, so Zn²⁺ is 3d¹⁰.
Calling Sc³⁺ coloured because scandium is a transition element.
Using the spin-only formula with paired electrons counted.
A practice routine
Write the atom and M²⁺ configurations for Sc to Zn from memory and mark each as complete or incomplete d.
Answer NCERT intext question 4.2 in two sentences.
Classify Cd and Hg using the same two-step test.
Compute spin-only moments for Mn²⁺, Fe²⁺ and Ni²⁺ and compare them with NCERT's table.
Test yourself again after three days; Dunlosky and colleagues (2013) rated spaced practice and practice testing as high utility.
If d-orbital filling still feels shaky, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, each with its own lesson.
Today, explain to someone in one minute why copper is a transition metal and zinc is not.
