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ChemistryMediumClass 12

Group 15 ā€” Nitrogen family, allotropes of P, structures

p-block Elements (Class 12 ā€” Groups 15, 16, 17, 18)

10

JEE Qs

8%

Hard

75

min

Prioritize understanding the anomalous behavior of Nitrogen and the structural and property differences among the allotropes of Phosphorus, along with key reactions.

šŸ§® Key Formulas

Nā‰”N (triple bond in dinitrogen)
P4 (tetrahedral structure of white phosphorus)
P4 + 3NaOH + 3H2O ā†’ PH3 + 3NaH2PO2 (Disproportionation of white P)
NH4Cl + NaNO2 ā†’ N2 + 2H2O + NaCl (Preparation of N2 from ammonium nitrite)

āœ… Key Points for JEE

  • 1Nitrogen exhibits anomalous behavior due to its small size, high electronegativity, high ionization enthalpy, absence of d-orbitals, and ability to form stable pĻ€-pĻ€ multiple bonds.
  • 2Understand the general periodic trends down Group 15 for atomic and physical properties (atomic size, ionization enthalpy, electronegativity, metallic character, melting/boiling points, density).
  • 3Master the preparation, properties, and structural differences of the allotropes of Phosphorus: White P (discrete P4 tetrahedral, highly reactive, poisonous, luminescent), Red P (polymeric, less reactive, non-poisonous), and Black P (most stable).
  • 4Focus on the distinct chemical reactivity trends down the group, especially towards hydrogen (hydrides), oxygen (oxides), halogens (halides), and metals, noting the preferred oxidation states.
  • 5Memorize key specific reactions like the preparation of N2 and the disproportionation of white phosphorus in alkali.

āš ļø Common Mistakes

  • āœ•Confusing the stability and reactivity differences between white, red, and black phosphorus; specifically, the high reactivity and poisonous nature of white P vs. the inertness of red P.
  • āœ•Incorrectly applying general p-block trends to nitrogen without considering its anomalous behavior, especially regarding its inability to expand its octet and form d-orbital mediated bonds.
  • āœ•Overlooking the structural details of P4 (tetrahedral) and how it leads to ring strain and high reactivity, compared to the polymeric structures of red and black phosphorus.

NCERT Chapters

  • Class 12 Chemistry Part I Ch 7: The p-Block Elements