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Lesson 2 General Physical and Chemical Properties of Transition Elements
├── Atomic mass
├── Atomic radius
├── Metallic character
├── Magnetic properties
└── Catalytic activity

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Atomic mass

Some data (the book’s table
for illustration only):

Element	Atomic mass	Atomic radius (Å)	Density (g/cm³)	m.p. (°C)	b.p. (°C)
Sc	45	1.44	3.10	1397	3900
Ti	47.9	1.32	4.42	1680	3130
V	51	1.22	6.07	1710	3530
Cr	52	1.17	7.19	1890	2480
Mn	54.9	1.17	7.21	1247	2087
Fe	55.9	1.16	7.87	1538	2800
Co	58.9	1.16	8.70	1490	3520
Ni	58.7	1.15	8.90	1492	2800
Cu	63.5	1.17	8.92	1083	2582

Atomic mass→increases gradually with atomic number (nickel is slightly abnormal: it has five stable isotopes giving an average of 58.7 u, so it is lighter than expected relative to Co).

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Atomic radius

Atomic radius→changes only a little along the series and is almost constant from Cr to Cu. Two opposing factors are responsible:

Comparison aspect	Main idea	Keywords
Decrease	effective nuclear charge rises and electrons are added so attraction to the electrons increases (Sc → Cr)	effectivenuclearchargerises
Increase	as 3d electrons increase repulsion between them increases. The two effects nearly cancel so radii are nearly constant — one reason these metals mix easily to make alloys (atoms of nearly equal size replace one another in the lattice)	electronsrepulsionbetweenthem

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Metallic character

Metallic character

all are solids with metallic lustre and good conduction of heat and electricity; they have high melting and boiling points because the metallic bond is strong (both 4s and 3d electrons take part in it); most have high density, which rises with atomic number since the size is almost constant while the mass grows.
Chemical activity varies copper is of low activity, iron is moderate (rusts in moist air), and scandium is very active (displaces hydrogen from water strongly).

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Magnetic properties

Magnetic properties

Comparison aspect	Main idea	Keywords
Paramagnetic	substances (atoms ions or molecules with unpaired electrons) are attracted into an external magnetic field. A spinning unpaired electron creates a tiny magnetic field. The magnetic moment increases with the number of unpaired electrons measuring the magnetic moment therefore tells us how many unpaired electrons there are. Most transition-element compounds are paramagnetic	substancesatomsionsmolecules
Diamagnetic	substances have all electrons paired the opposite spins cancel the magnetic moment is zero and they are weakly repelled by a magnetic field	substanceselectronspairedopposite

Species	d configuration	Unpaired e⁻	Behaviour
Zn (or Zn²⁺)	d¹⁰	0	diamagnetic
Ni²⁺	d⁸	2	paramagnetic
Fe²⁺ (FeCl₂)	d⁶	4	paramagnetic
Fe³⁺ (FeCl₃)	d⁵	5	paramagnetic
Co²⁺ (CoCl₂)	d⁷	3	paramagnetic
Cr³⁺ (Cr₂O₃)	d³	3	paramagnetic
Ti⁴⁺ (TiO₂)	d⁰	0	diamagnetic

Ascending order of magnetic moment for FeCl₂, Cr₂O₃, TiO₂→TiO₂ (0) < Cr₂O₃ (3) < FeCl₂ (4).

✍️ Worked examples

Comparison aspect	Main idea	Keywords
Worked example 2.	Classify as paramagnetic or diamagnetic: CoCl₂ FeSO₄ ZnSO₄ FeCl₃ and arrange them by increasing magnetic moment	ClassifyparamagneticdiamagneticCoCl₂
Co²⁺ (in CoCl₂)	3d⁷ → 3 unpaired → paramagnetic	unpairedparamagnetic
Fe²⁺ (in FeSO₄)	3d⁶ → 4 unpaired → paramagnetic	unpairedparamagnetic
Zn²⁺ (in ZnSO₄)	3d¹⁰ → 0 unpaired → diamagnetic	3d¹⁰unpaireddiamagnetic
Fe³⁺ (in FeCl₃)	3d⁵ → 5 unpaired → paramagnetic. Order: ZnSO₄ (0) < CoCl₂ (3) < FeSO₄ (4) < FeCl₃ (5)	unpairedparamagneticOrderZnSO₄
•	Worked example 3	Workedexample
Mn²⁺, Cu⁺ and Cu²⁺	Mn²⁺ is 3d⁵ (5 unpaired paramagnetic) Cu⁺ is 3d¹⁰ (0 diamagnetic) Cu²⁺ is 3d⁹ (1 paramagnetic)	unpairedparamagnetic3d¹⁰diamagnetic
•	So Cu⁺ compounds are colourless diamagnetic solids in contrast with Cu²⁺ compounds which are paramagnetic	compoundscolourlessdiamagneticsolids

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Catalytic activity

Catalytic activity→transition metals and their compounds are ideal catalysts:

finely divided Ni — hydrogenation of oils;

finely divided Fe — Haber–Bosch N₂ + 3H₂ ⇌ 2NH₃ (about 500 °C, 200 atm);
V₂O₅ — contact process 2SO₂ + O₂ ⇌ 2SO₃, then SO₃ + H₂O → H₂SO₄ (via oleum);
MnO₂ — decomposition of hydrogen peroxide 2H₂O₂ → 2H₂O + O₂ (the catalyst gives a lower-energy path, so the activation-energy barrier on the energy diagram is lower while the net energy released by the forward reaction is unchanged).
Reason:
the 4s and 3d electrons can form temporary bonds between the metal-surface atoms and the reacting molecules.
This raises the concentration of reactants on the surface, weakens bonds inside the reactant molecules and so lowers the activation energy, increasing the reaction rate.
Their ability to exist in several oxidation states also helps them form intermediates.
A catalyst is not consumed, and it does not change the position of equilibrium or the heat of reaction.

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Part 7

📖

🔍 In-Depth Explanations, Deductions & Multi-Book Insights:

Chemistry Thanaweya Amma (2026/2027)

Lesson 2 – General Physical and Chemical Properties of Transition Elements
Detailed Academic Lesson Overview:
The 3d elements exhibit unique physical and chemical characteristics: atomic radius stability across the series, variable oxidation states, catalytic activity, magnetic behaviors (paramagnetism vs. diamagnetism), and colored ions.

🌳 Hierarchy Classification & Conceptual Roadmap

Properties of 3d Elements

├── 1. Atomic Radius & Density

│ ├── Near-constant atomic radius from Cr to Cu due to two opposing factors
│ └── Density increases regularly across the series due to mass increase with constant volume

├── 2. Magnetic Properties & Magnetic Moment (μ)

│ ├── ParamagneticContains unpaired electrons in 3d; attracted to external magnetic field

│ └── DiamagneticAll electrons paired in 3d; slightly repelled by external magnetic field

└── 3. Catalytic Activity & Colored Complexes

Comparison aspect	Main idea	Keywords
├── Superior catalysis	Uses 4s and 3d electrons to form temporary bonds with reactants	Useselectronsformtemporary
└── Colored ions	Absorption of visible light photons to excite unpaired 3d electrons	Absorptionvisiblelightphotons
•	📋 Master Teacher's Blackboard Rules & Exam Secrets	MasterTeacherBlackboardRules
RULE 1	Magnetic moment (μ) increases with the number of unpaired electrons in 3d peaking at Mn²⁺ and Fe³⁺ (5 unpaired electrons μ ≈ 5.9 BM)	Magneticmomentincreasesnumber
RULE 2	Zn²⁺ Sc³⁺ and Ti⁴⁺ are diamagnetic and colorless because they contain zero unpaired electrons in 3d (either 3d⁰ or 3d¹⁰)	diamagneticcolorlessbecausecontain
RULE 3	If an ion absorbs red light it appears green to the human eye (its complementary color). If it absorbs all visible light it appears black if it reflects all it appears white	absorbslightappearsgreen
📊 Detailed Comparison Matrix	Absorbed Colors and Complementary Colors in Transition Chemistry	AbsorbedColorsComplementaryTransition

Absorbed Color	Complementary Color Seen	Aqueous Transition Example
Red	Green	Cr³⁺ hydrated ions (appear green)
Orange	Blue	Cu²⁺ hydrated ions (appear blue)
Yellow	Violet / Purple	Fe³⁺ / KMnO₄ solutions
Violet	Yellow	Fe²⁺ diluted solutions
Blue	Orange	Dichromate (Cr₂O₇²⁻) acidic solution

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Curriculum

Chemistry

Chapter 1 - Transition Elements and Iron Metallurgy

Chapter 2 - Chemical Analysis

Chapter 3 - Chemical Equilibrium

Chapter 4 - Electrochemistry

Chapter 5 - Organic Chemistry

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Lesson 2: General Physical and Chemical Properties of Transition Elements