---
title: "Transition elements; oxidation states of 3d; alloys"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:tm-ox-alloy"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tm-ox-alloy
site: BCT Engineering
---

# Transition elements; oxidation states of 3d; alloys

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

- Asked in: 2067 Mangsir, 1+3+1 marks
- Video: [8.2- d~Block elements , physical properties [Variable Oxidation States of transition elements ]](https://www.youtube.com/watch?v=nxwnRJDHt2s) — IPL CHEMISTRY
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tm-ox-alloy
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

What are transition elements? Explain the variable oxidation states exhibited by 3d series. Why does the transition elements form alloy?

## Short answer

Transition elements have partly filled d-subshell. Variable oxidation states occur because 4s and 3d electrons have similar energy, enabling both to bond; states differ by one unit (e.g., Mn +2 to +7). Alloy formation is possible due to similar atomic radii, allowing atom substitution in lattices, e.g., steel and brass.

## Answer

#### Transition elements
Transition elements are the d-block elements that have a partly filled d-subshell in the atom or in at least one of their common oxidation states. The 3d series is Sc to Zn (general outer configuration (n−1)d¹⁻¹⁰ ns¹⁻²).

#### Variable oxidation states
Variable oxidation states arise because the 4s and 3d electrons have very similar energies, so both 4s and some or all 3d electrons can be used in bonding. The states differ by one unit (Fe²⁺, Fe³⁺), unlike the p-block where they differ by two.

```text
Ti  +2 +3 +4          Fe  +2 +3
V   +2 +3 +4 +5       Co  +2 +3
Cr  +2 +3 +6          Ni  +2
Mn  +2 +3 +4 +6 +7    Cu  +1 +2
```
- Minimum oxidation state is usually +2 (loss of the two 4s electrons); the maximum equals the total number of 4s + 3d electrons, reached at Mn (+7).
- Stability of higher states falls after Mn because the nuclear charge holds the 3d electrons more tightly.
- Half-filled d⁵ (Mn²⁺, Fe³⁺) and filled d¹⁰ (Zn²⁺) are specially stable.

#### Alloy formation
Transition metals have similar atomic radii, so atoms of one metal can replace atoms of another in the crystal lattice without disturbing the structure. They therefore form alloys readily, such as steel (Fe–C–Cr–Ni), brass (Cu–Zn) and bronze (Cu–Sn).

## Check yourself

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

1. Transition elements are those with
   A. a full d subshell in all states
   B. a partly filled d subshell in the atom or in a common oxidation state
   C. no d orbitals
   D. only p electrons
   Answer: B. The correct option is: a partly filled d subshell in the atom or in a common oxidation state. This follows from the answer on definition. (Key point: Definition)

2. Why do 3d elements show variable oxidation states?
   A. 4s is far above 3d
   B. 3d are not involved
   C. 4s and 3d energies are similar
   D. They have one electron only
   Answer: C. Both can be used for bonding. (Key point: Variable states reason)

3. Which ions are specially stable?
   A. d2
   B. d3 only
   C. d4 only
   D. d5 (Mn2+, Fe3+) and d10 (Zn2+)
   Answer: D. Half-filled and filled d subshells are stable. (Key point: Stability)

4. Why do they form alloys?
   A. Similar atomic radii allow atoms to replace one another in the lattice
   B. Very different radii
   C. They are gases
   D. No metallic bonding
   Answer: A. Steel, brass and bronze are examples. (Key point: Alloys)

## Related in Engineering Chemistry

- [Variable oxidation states of 3d elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Avariable-oxidation-3d) — Engineering Chemistry, chapter 5, asked 6×
- [Variable oxidation states; industrial uses of 3d elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Avariable-ox-applications) — Engineering Chemistry, chapter 5
- [First-row configuration; variable oxidation states](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aconfig-variable-oxidation) — Engineering Chemistry, chapter 5
- [Transition elements; non-typical 3d element](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-not-typical) — 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
- [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