Revision: Std XII >> Transition and Inner Transition Elements MAH-MHT CET (PCM/PCB) Transition and Inner Transition Elements

The elements in which the last electron enters the d-orbital of penultimate shell, i.e. (n – 1) d orbital, where n is the outermost shell, are known as d-block elements or transition elements.

The minerals which contain high percentage of atom and from which a metal can be extracted conveniently and profitably are called ores, e.g. bauxite is an ore of aluminium.

The science and technology regarding the extraction of metals from ores and their purification for use is called metallurgy.

The naturally occurring chemical substances in the earth’s crust, containing inorganic salts, solid silicons, matte, etc., obtainable by mining, are called minerals, e.g. bauxite and kaolinite.

Roasting is the process of heating concentrated ore to a high temperature in the presence of air. The process is usually carried out for sulphide ores.

The product obtained by the combination of gangue with flux is called slag.

The substance added to get rid of gangue in the extraction of metal is called flux.

Most of the elements occur in nature as in combined state as minerals. The chemical composition of minerals is fixed.

Minerals from which metals can be extracted profitably are known as ores.

If minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it. These minerals are called ores.

If an ore is a carbonate or a hydrated oxide, it is heated in the absence of air to a temperature that is high but insufficient to melt the ore. The process is known as calcination.

The impurities (sand, silt, soil, gravel, etc.) present in the ore are called gangue.

Elements with atomic numbers greater than 92 are called Transuranium.

The elements beyond lawrencium, element number 103. Elements from atomic number 93 to 103 are now included in the actinoid series, and those from 104 to 118 are called postactinoid elements.

Trends in Atomic Properties:

• Radius ↓ (Sc → Zn)
• Ionisation enthalpy ↑ (irregular)
• Oxidation states variable (+2, +3 common)
• Magnetic → due to unpaired e⁻
• Metallic nature present

General Properties:

• Colour → d–d transition (d⁰, d¹⁰ = colourless)
• Complex formation → vacant d-orbitals
• Catalysis → variable oxidation states
• Interstitial compounds → hard, high m.p.
• Alloys → due to similar size

Potassium Permanganate (KMnO₄)

Preparation:

2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O

K₂MnO₄ → KMnO₄ (by oxidation)

Chemical Properties:

Acidic medium:

• MnO₄⁻ → Mn²⁺

Oxidises:

• I⁻ → I₂
• Fe²⁺ → Fe³⁺
• S²⁻ → S
• H₂C₂O₄ → CO₂

Neutral / Alkaline medium:

MnO₄⁻ → MnO₂

I⁻ → IO₃⁻

Potassium Dichromate (K₂Cr₂O₇)

Preparation:

• FeCr₂O₄ → Na₂CrO₄ (fusion)
• Na₂CrO₄ → Na₂Cr₂O₇ (acidification)
• Na₂Cr₂O₇ → K₂Cr₂O₇ (with KCl)

Chemical Properties (Acidic medium):

• Cr₂O₇²⁻ → Cr³⁺

Oxidises:

• I⁻ → I₂
• S²⁻ → S

Physical Properties: 

• Lustrous, hard, high-density

• High melting & boiling points

• Good conductors (heat & electricity)

• Malleable + high tensile strength

• Paramagnetic (due to unpaired electrons)

• Good catalysts 

Chemical Properties:

• Electropositive metals

• Show variable oxidation states

• Form coloured compounds & complexes

• Act as good reducing agents

• Form insoluble oxides & hydroxides

• Some metals (Fe, Co, Cu, Mo, Zn) are biologically important

• Catalyse biological reactions

• Reactive metals occur in combined form (as oxides, sulphides, etc.), while unreactive metals like gold and silver occur in the free state.
• Minerals are natural metal compounds; those from which metals can be extracted economically are called ores, and impurities present in ores are called gangue.
• The complete process of extracting and purifying metals from ores is called metallurgy.

Physical Properties:

• Silvery white, soft metals with moderate density
• Good conductors of heat and electricity

Basic Character:

• Hydroxides are ionic and basic
• Basicity decreases from La(OH)₃ to Lu(OH)₃

Ionisation Enthalpy:

• Gradually decreases from La to Lu with irregularities

Oxidation States:

• The most common oxidation state is +3
• Also show +2 and +4

Colour and Spectra:

• Colour due to f–f transitions

Atomic and Ionic Radii (Lanthanoid Contraction):

• Radii decrease from La to Lu
• Due to the poor shielding of the 4f electrons

Magnetic Property:

• Most lanthanoids are paramagnetic

Chemical Reactivity:

• Form:
  • Oxides: Ln₂O₃
  • Hydroxides: Ln(OH)₃
  • Halides: LnX₃
  • Nitrides: LnN
  • Carbides: LnC₂

General electronic configuration: \[[Xe]4f^{0-14}5d^{0-2}6s^{2}\]

• Elements in which the last electron enters the 5f-orbital (Th to Lr)
• Second inner transition series (Z = 90 to 103)
• General electronic configuration: \[5f^{1-14},6d^{0-1},7s^{2}\]
• Show irregular electronic configurations
• Stability associated with f⁰, f⁷, f¹⁴ configurations
• Examples of exceptions:
  • Am: [Rn] 5f⁷ 7s²
  • Cm: [Rn] 5f⁷ 6d¹ 7s²

• Silvery white metals with high density and high melting/boiling points
• All are radioactive
• Show variable oxidation states (common: +3; higher states in early elements)
• Strong reducing agents and highly reactive
• React with O₂, halogens, H₂, S (similar to lanthanoids)
• React with hot water to form hydroxides and H₂ gas
• Atomic and ionic radii decrease from Ac to Lr (actinoid contraction)
• 5f orbitals show poor shielding → irregular electronic configuration
• Electron distribution in 5f orbitals is less certain than 4f (lanthanoids)