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Overview of Transition and Inner Transition Elements

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Estimated time: 46 minutes
Maharashtra State Board: Class 12

Definition: Transition elements

Elements of d-block having incompletely filled (n–1)d orbitals in their atom or in common oxidation states are called transition elements.

Maharashtra State Board: Class 12

Definition: Oxidation state

The charge acquired by an atom when it loses or gains electrons in a compound is called oxidation state.

Maharashtra State Board: Class 12

Definition: Ionisation enthalpy

The energy required to remove an electron from an isolated gaseous atom is called ionisation enthalpy.

Maharashtra State Board: Class 12

Definition: Paramagnetic substance

Substances that are attracted by an external magnetic field due to presence of unpaired electrons are called paramagnetic.

Maharashtra State Board: Class 12

Definition: Diamagnetic substance

Substances that are repelled by a magnetic field and have all electrons paired are called diamagnetic.

Maharashtra State Board: Class 12

Definition: Magnetic moment

The magnetic strength of a substance due to unpaired electrons is called magnetic moment.

Maharashtra State Board: Class 12

Definition: Alloy

A homogeneous mixture of two or more metals or a metal with a non-metal is called an alloy.

Maharashtra State Board: Class 12

Definition: Ferrous alloys

Alloys containing iron as the main metal are called ferrous alloys.

Maharashtra State Board: Class 12

Definition: Non-ferrous alloys

Alloys that do not contain iron as the main metal are called non-ferrous alloys.

Maharashtra State Board: Class 12

Definition: Interstitial compounds

Compounds formed when small atoms like H, C or N occupy interstitial spaces in the crystal lattice of metals are called interstitial compounds.

Maharashtra State Board: Class 12

Definition: Catalyst

A substance that increases the rate of a chemical reaction without being consumed is called a catalyst.

Maharashtra State Board: Class 12

Definition: Metallurgy

The process of extraction of metals from their ores is called metallurgy.

Maharashtra State Board: Class 12

Definition: Mineral

A naturally occurring substance in the earth’s crust containing metal or its compounds is called a mineral.

Maharashtra State Board: Class 12

Definition: Ore

A mineral from which metal can be extracted economically is called an ore.

Maharashtra State Board: Class 12

Definition: Pyrometallurgy

Extraction of metal from ore by heating at high temperature is called pyrometallurgy.

Maharashtra State Board: Class 12

Definition: Hydrometallurgy

Extraction of metal from aqueous solution of its ore using suitable reducing agent is called hydrometallurgy.

Maharashtra State Board: Class 12

Definition: Electrometallurgy

Extraction of metal by electrolysis of molten compound is called electrometallurgy.

Maharashtra State Board: Class 12

Definition: Oxidising agent

A substance that gains electrons and causes oxidation of another substance is called an oxidising agent.

Maharashtra State Board: Class 12

Definition: Gangue

The unwanted impurities like sand, clay, etc., present in an ore are called gangue.

Maharashtra State Board: Class 12

Definition: Calcination

Heating of carbonate ore in limited or no air to remove volatile impurities is called calcination.

Maharashtra State Board: Class 12

Definition: Inner transition elements

The f-block elements placed separately at the bottom of periodic table are called inner transition elements.

Maharashtra State Board: Class 12

Definition: Lanthanoids

The series of 14 elements from atomic number 57 to 71 in which 4f orbitals are progressively filled are called lanthanoids.

Maharashtra State Board: Class 12

Definition: Actinoids

The series of elements from atomic number 89 to 103 in which 5f orbitals are progressively filled are called actinoids.

Maharashtra State Board: Class 12

Definition: Lanthanoid contraction

The gradual decrease in atomic and ionic radii of lanthanoids with increase in atomic number is called lanthanoid contraction.

Maharashtra State Board: Class 12

Definition: Actinoid contraction

The gradual decrease in atomic and ionic radii across the actinoid series is called actinoid contraction.

Maharashtra State Board: Class 12

Definition: Ionization enthalpy

The energy required to remove an electron from an isolated gaseous atom is called ionization enthalpy.

Maharashtra State Board: Class 12

Key Points: Oxidation states and physical properties of first transition series elements

  1. Transition elements show variable oxidation states because they can lose different numbers of 3d and 4s electrons.
  2. The number of oxidation states increases with the increase in the number of unpaired electrons in the 3d orbitals.
  3. Manganese shows the maximum number of oxidation states in the first transition series, ranging from +2 to +7.
  4. All transition elements are metals and generally show typical metallic properties such as hardness, malleability, ductility, and good conductivity of heat and electricity.
  5. Transition metals have high melting and boiling points and form alloys with other metals; however, zinc, cadmium, and mercury are exceptions in some properties.
Maharashtra State Board: Class 12

Key Points: Properties and Trends of First Transition Series Elements

Property General Trend Reason Example Important Note
Atomic Radii Decrease gradually from Sc to Zn Increase in effective nuclear charge; poor shielding by d-electrons Sc (164 pm) > Fe (126 pm) Minor irregular variations occur
Ionic Radii Decrease with increase in oxidation state Higher nuclear charge pulls electrons closer Cr²⁺ (82 pm) > Cr³⁺ (62 pm) M³⁺ ions smaller than M²⁺
Ionisation Enthalpy Slight overall increase across the series Gradual increase in nuclear charge Zn has highest IE₁ (906 kJ/mol) IE₁ < IE₂ < IE₃ for each element
Metallic Character Strong metallic properties Low ionisation enthalpy and presence of d-electrons Fe, Co, Ni Hard, high melting and boiling points
Magnetic Properties Depends on number of unpaired electrons μ = √n(n+2) BM (spin-only formula) Mn²⁺ (5.92 BM) Zn²⁺ is diamagnetic
Colour of Ions Most ions are coloured Due to d–d electronic transitions Cu²⁺ (Blue), Fe³⁺ (Yellow) d⁰ and d¹⁰ ions are colourless
Catalytic & Alloy Formation Show catalytic activity and form alloys Variable oxidation states and similar atomic radii Fe (Haber process), Stainless steel Widely used in industry
Maharashtra State Board: Class 12

Key Points: Properties of d block elements

  1. d-block elements are lustrous, hard, and dense metals with high melting and boiling points and good conductivity.
  2. They form alloys and show paramagnetism, and most of them act as efficient catalysts.
  3. They are electropositive and exhibit variable oxidation states, forming coloured salts and complexes.
  4. They act as good reducing agents and generally form insoluble oxides and hydroxides.
  5. Some d-block elements are biologically important, such as Fe, Co, Cu, Mo, and Zn.
  6. Higher oxidation states are more stable in second and third transition series; the maximum oxidation state is +7 in the first row and +8 in the third row.
 
Maharashtra State Board: Class 12

Key Points: Properties of f-block elements

  1. f-block elements are similar to d-block elements and involve filling of (n–2)f orbitals. They are placed between (n–1)d and ns block elements in the periodic table.
  2. Lanthanoids (atomic numbers 57–71) are called rare earth elements, though they are relatively abundant but difficult to separate due to similar chemical properties.
  3. They are soft, reactive metals with moderate density and high melting and boiling points, resembling alkali and alkaline earth metals in reactivity.
  4. The most common oxidation state is +3, while some elements also show +2 and +4 oxidation states (e.g., Eu²⁺, Yb²⁺, Ce⁴⁺).
  5. Lanthanoids show contraction in ionic radii (lanthanoid contraction) and form basic hydroxides; many of their ions are coloured due to electronic transitions.
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