---
title: "Why d-block elements are called transition"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:why-transition-elements"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/why-transition-elements
site: BCT Engineering
---

# Why d-block elements are called transition

Engineering Chemistry · Chapter 5: 3-d Transition Elements and their Applications

- Asked in: 2075 Baisakh, 1+2 marks; 2072 Asoj, 2 marks (asked 2 times)
- Video: [What are transition elements? and Why are they called so?](https://www.youtube.com/watch?v=EMGfj3CKS5c) — Explained Chemistry
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/why-transition-elements
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

Why are transition elements called so? Are all d-block elements transition elements? Justify your answer with reason.

## Short answer

They are called transition elements because their properties are transitional between s-block (electropositive) and p-block (electronegative) elements. By IUPAC definition, a transition element must have an incompletely filled d subshell in the atom or a common ion. Not all d-block elements are transition; Zn, Cd and Hg have d¹⁰ in atom and M²⁺ ion, so they are d-block but not transition.

## Answer

#### Why they are called transition elements
The d-block elements lie between the s-block (strongly electropositive, ionic compounds) and the p-block (electronegative, covalent compounds). Their properties are transitional between these two, so they are called **transition elements**. By the IUPAC definition, a transition element is one that has an incompletely filled d subshell, either in the atom or in any of its common ions.

#### Are all d-block elements transition elements?
**No.** Zn, Cd and Hg (group 12) have the configuration (n−1)d¹⁰ ns² in the atom and the d¹⁰ configuration in their only common ion (M²⁺ = d¹⁰). The d subshell is completely filled in both, so they do not show the typical transition properties (variable oxidation states, coloured ions, paramagnetism, strong catalytic activity). They are d-block elements but not transition elements. Cu (Cu²⁺ is d⁹) and Sc (Sc has 3d¹ in the atom) are considered transition elements because of the incomplete d subshell in the atom or in a common ion.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why are d-block elements called transition elements?
   A. Their properties are transitional between s-block and p-block
   B. They transit across space
   C. They only change state
   D. They are radioactive
   Answer: A. They lie between the electropositive s-block and electronegative p-block. (Key point: Name origin)

2. Which defines a transition element?
   A. Any element in group 3 to 12
   B. Incompletely filled d subshell in the atom or a common ion
   C. Any element with an s electron
   D. Only elements with full d
   Answer: B. This is the IUPAC definition. (Key point: IUPAC definition)

3. Why are Zn, Cd, Hg not transition elements?
   A. They have d5
   B. They have no electrons
   C. They have d10 in both the atom and the M2+ ion
   D. They are gases
   Answer: C. The d subshell is completely filled. (Key point: Zn Cd Hg)

4. Why is Cu considered a transition element?
   A. Cu2+ is d10
   B. Cu has no d electrons
   C. Cu is an s-block metal
   D. Cu2+ is d9, an incomplete d subshell
   Answer: D. Incomplete d in a common ion qualifies it. (Key point: Cu)

## Related in Engineering Chemistry

- [Transition elements; why so called; 3d configurations](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-called-config) — Engineering Chemistry, chapter 5
- [Why 3d elements are transition; valency characteristics](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3A3d-transition-valency) — Engineering Chemistry, chapter 5
- [d-block elements; 3d configuration; non-typical metals](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Adblock-config-not-typical) — Engineering Chemistry, chapter 5
- [Complex formation by transition elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Acomplex-formation-tm) — Engineering Chemistry, chapter 5, asked 11×
- [Transition elements; first series configuration](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awhy-transition-elements-typical) — Engineering Chemistry, chapter 5
- [Transition elements; configuration; paramagnetism](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-config-paramagnetism) — Engineering Chemistry, chapter 5

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