Nitrogen Family Lecture Notes

Introduction

• Discussing the nitrogen family (Group 15 elements).
• Expected questions from this part of the chapter.
• Changed slides for better appearance.
• Nitrogen family coverage includes: Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi), Moscovium (Mc).
• Group 15 elements have significant breadth and expected to take over two and a half hours to cover completely.
• PDF notes will be provided after completing the chapter.

Group 15 Elements

Characteristics

• Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth, and Moscovium.
• Moscovium is synthetic and radioactive, less discussed.
• Arsenic (As) and Antimony (Sb) are metalloids; Nitrogen (N) and Phosphorus (P) are non-metals; Bismuth (Bi) is a metal.
• Electronic Configuration: ns²np³, with a half-filled p-orbital providing extra stability ns² np³ leading to -3, +3, +5 oxidation states.

Properties

Atomic and Ionic Radii

• Increases down the group.
• From N to P, there is a significant increase. From As to Bi, there is a smaller increase due to poor shielding of d and f orbitals.

Ionization Enthalpy

• Decreases down the group.
• Higher for N than P, lower as you move downwards.

Electronegativity

• Decreases down the group.
• Higher for As and Sb compared to their neighbors due to the poor shielding of f orbitals.

Density

• Increases down the group.

Physical Properties

• Boiling point and melting point trends, especially noting the strong hydrogen bonding in NH₃.
• Phosphorus comes in three allotropes: white, red, and black (alpha and beta).

Chemical Properties

Oxidation States

• Common oxidation states: -3, +3, +5.
• Stability of +5 decreases & +3 increases as you move down due to inert pair effect.
• Isomers can exist in different oxidation states.
• Specific behavior of Bismuth showing only BiF₅.

Hydrides

• Types: NH₃, PH₃, AsH₃, SbH₃, BiH₃.
• Thermal Stability: Decreases down the group.
• Reducing Nature: Increases down the group.
• Basicity: Decreases down the group.

Halides

• Forms trihalides (MX₃) and pentahalides (MX₅).
• Trihalides are more covalent than pentahalides.
• Nitrogen cannot form MX₅.

Oxides

• Variation in acidity/basicity
• Basicity: Increases down the group.
• Higher oxidation state oxides are more acidic.

Preparation and Uses

Nitrogen (N₂)

• Commercial: Fractional distillation of liquefied air.
• Laboratory Methods:
  • Ba(N₃)₂ → Ba + 3N₂
  • NH₄Cl + NaNO₂ → N₂ + H₂O + NaCl
  • (NH₄)₂Cr₂O₇ → N₂ + Cr₂O₃ + H₂O

Ammonia (NH₃)

• Haber’s Process: N₂ + 3H₂ → 2NH₃
  • Catalyst: Iron
  • Temp: 773 K
  • Pressure: 200 atm
• Physical Properties: Colorless, pungent smell, trigonal pyramidal shape.
• Ammonia as a Lewis base forms complex compounds.

Nitric Acid (HNO₃)

• Preparation:
  • Laboratory: NaNO₃ + H₂SO₄ → HNO₃ + NaHSO₄
  • Oswald Process:
    • 4NH₃ + 5O₂ → 4NO + 6H₂O
    • 2NO + O₂ → 2NO₂
    • 4NO₂ + 2H₂O → 2HNO₃ + NO
• Properties of HNO₃ and reaction behavior.

Allotropes of Phosphorus

White Phosphorus

• Highly reactive, tetrahedral structure, spontaneous combustion in air.

Red Phosphorus

• Less reactive, polymeric structure, formed by heating white phosphorus.

Black Phosphorus

• Alpha Black: Formed at higher temperatures (803 K), does not oxidize in air.
• Beta Black: Formed at lower temperatures (473 K), remains stable in air.

Phosphine (PH₃)

Preparation

• Ca₃P₂ + 6H₂O → 3Ca(OH)₂ + 2PH₃
• P₄ + NaOH + H₂O → PH₃ (from white phosphorus)

Oxoacids of Phosphorus

Types and Structures

• H₃PO₂: Hypophosphorous acid (Reducing agent).
• H₃PO₃: Orthophosphorous acid.
• H₄P₂O₅: Pyrophosphorous acid.
• H₄P₂O₆: Hypophosphoric acid.
• H₃PO₄: Orthophosphoric acid.
• H₄P₂O₇: Pyrophosphoric acid.
• HPO₃: Metaphosphoric acid.
• All structures involve a central phosphorus atom with varying numbers of OH groups, P=O, and P-O-P bonds.

Reactions with Other Compounds of Interest

• Reaction trends with metals and non-metals, properties of phosphorous halides.

Conclusion

• We have covered key topics including: Nitrogen properties, oxides, and compounds; Phosphorus allotropes and compounds; Important preparation methods and reactions.