Transition Elements – Chemistry Notes

1. Introduction

Transition Elements: Elements that are found between group two and three of the periodic table.

General Properties:

Variable oxidation states
Form colored compounds
Good conductors of electricity and heat
Act as catalysts in many reactions
Form complex ions

2. Copper (Cu)

Atomic Number: 29

Electronic Configuration: [Ar] 3d¹⁰ 4s¹

Occurrence: Found as native copper, or as ores like Cu₂S (chalcocite), CuFeS₂ (chalcopyrite), CuCO₃.Cu(OH)₂ (malachite).

A. Physical Properties of Copper

Reddish-brown metal, malleable and ductile
Good conductor of electricity
High melting point: 1083°C

B. Chemical Properties of Copper

Does not react with cold water
Reacts with hot concentrated nitric acid to give NO₂ gas:
3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O
Reacts with concentrated sulfuric acid on heating:
Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O

C. Tests for Copper

Flame Test: Green-blue flame
Ammonia Test: Add NH₃(aq) to Cu²⁺ → deep blue complex [Cu(NH₃)₄]²⁺ forms
Sodium Hydroxide Test: Cu²⁺ + 2NaOH → Cu(OH)₂ (blue precipitate)

3. Iron (Fe)

Atomic Number: 26

Electronic Configuration: [Ar] 3d⁶ 4s²

Occurrence: Found as ores like Fe₂O₃ (hematite), Fe₃O₄ (magnetite), FeCO₃ (siderite).

A. Physical Properties of Iron

Silvery-gray metal, magnetic
Moderate melting point: 1538°C
Good conductor of heat and electricity

B. Chemical Properties of Iron

Reacts slowly with cold water, rapidly with steam to form Fe₃O₄: 3Fe + 4H₂O → Fe₃O₄ + 4H₂
Reacts with dilute acids to form salts and hydrogen: Fe + 2HCl → FeCl₂ + H₂
Forms oxides and hydroxides: Fe²⁺ (ferrous) and Fe³⁺ (ferric)

C. Tests for Iron

Fe²⁺ Test: Add NaOH → Fe(OH)₂ green precipitate; oxidizes to brown Fe(OH)₃
Fe³⁺ Test: Add K₃[Fe(CN)₆] → blue precipitate (Prussian blue)
Flame Test: Golden-yellow flame

4. Comparison of Cu and Fe

Property	Copper (Cu)	Iron (Fe)
Color	Reddish-brown	Silvery-gray
Melting Point	1083°C	1538°C
Oxidation States	+1, +2	+2, +3
Reaction with water	Does not react	Slowly reacts with cold water, rapidly with steam
Flame Test	Green-blue	Golden-yellow
OH⁻ Test	Cu²⁺ + 2OH⁻ → Cu(OH)₂ (blue)	Fe²⁺ + 2OH⁻ → Fe(OH)₂ (green); Fe³⁺ + 3OH⁻ → Fe(OH)₃ (brown)

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