---
title: "Why 3d elements are transition; valency characteristics"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:3d-transition-valency"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/3d-transition-valency
site: BCT Engineering
---

# Why 3d elements are transition; valency characteristics

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

- Asked in: 2069 Bhadra, 2+3 marks
- 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/3d-transition-valency
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

Why are 3d-series elements called transition elements? Give their characteristic on the basis of valency.

## Short answer

3d elements are called transition elements because they lie between s- and p-blocks of the periodic table and have an incomplete 3d subshell. They show variable valency as 4s and 3d electrons have similar energies, both take part in bonding; states differ by one unit, common +2, and highest oxidation number equals sum of 4s and 3d electrons up to Mn +7.

## Answer

#### Why 3d elements are called transition elements
The elements Sc to Zn lie between the s-block and p-block elements of the periodic table, and their properties change gradually from the strongly electropositive s-block metals to the less electropositive p-block elements. They have an incomplete 3d subshell, with electrons added to the inner (n−1)d orbitals, so they form a transition between the two blocks.

#### Characteristics based on valency (oxidation state)
- They show **variable valency** because 4s and 3d electrons have nearly equal energies and both take part in bonding.
- Common states: +2 (loss of both 4s electrons) for almost all; +3 for Sc, Ti, Cr, Fe, Co; Mn shows +2 to +7; Cu shows +1 and +2.
- Successive states differ by one unit (Fe²⁺, Fe³⁺), not by two.
- The highest oxidation state equals the sum of 4s and 3d electrons up to Mn (+7). Higher states are oxidising (MnO₄⁻, Cr₂O₇²⁻); lower states are reducing (Fe²⁺).
- Zn shows only +2 and Sc only +3.

## Check yourself

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

1. Why are 3d elements called transition elements?
   A. They transit to noble gases
   B. They lie between s-block and p-block and their properties change gradually between the two
   C. They are all radioactive
   D. They have no valence electrons
   Answer: B. Their properties are transitional between electropositive s-block and less electropositive p-block elements. (Key point: Why 'transition')

2. Why do they show variable valency?
   A. Only 4s electrons exist
   B. Only 3d are used
   C. 4s and 3d electrons have nearly equal energies and both take part in bonding
   D. They have fixed valency
   Answer: C. Similar energies allow multiple states. (Key point: Cause of valency)

3. How do successive oxidation states differ?
   A. By two units
   B. By three units
   C. They do not differ
   D. By one unit, e.g. Fe2+ and Fe3+
   Answer: D. Not by two as in the p-block. (Key point: Step)

4. Which statement is correct?
   A. Higher states (MnO4-) are oxidising; lower states (Fe2+) are reducing
   B. Higher states are reducing
   C. Lower states are oxidising
   D. Both are always inert
   Answer: A. Higher states tend to gain electrons; lower states tend to lose them. (Key point: Oxidising/reducing)

## 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
- [Main characteristics of 3d transition elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3A3d-characteristics) — Engineering Chemistry, chapter 5
- [Why d-block elements are called transition](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awhy-transition-elements) — Engineering Chemistry, chapter 5, asked 2×
- [Transition elements; non-typical 3d element](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-not-typical) — Engineering Chemistry, chapter 5
- [Transition elements; oxidation states of 3d; alloys](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-ox-alloy) — Engineering Chemistry, chapter 5
- [Transition elements; industrial uses of 3d elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-industrial-applications) — Engineering Chemistry, chapter 5

## Related in other subjects

- [Elements of transition curve](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atransition-curve-elements) — Surveying II, chapter 6
- [2D and 3D mesh elements, prism layers](https://www.bctengineer.com/question.md?key=semester_7%2Fapplied_computational_fluid_dynamics%3Amesh-element-types-prism-layers) — Applied Computational Fluid Dynamics, chapter 4