Chemical Reaction of Ammonium Chloride and Sodium Nitrite

Group 15 Elements: Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth

• The +3 oxidation state of arsenic, antimony, and bismuth becomes increasingly stable with respect to disproportionation.

Nitrogen's Anomalous Properties

• Nitrogen differs from the rest of the group due to its small size, high electronegativity, high ionization enthalpy, and non-availability of d orbitals.
• Nitrogen has a unique ability to form pπ-pπ multiple bonds with itself and with other elements having small size and high electronegativity (e.g., C, O).
• Nitrogen exists as a diatomic molecule with a triple bond (one s and two p) between the two atoms, resulting in a very high bond enthalpy (941.4 kJ mol).

Properties of Nitrogen

• Nitrogen forms a single N-N bond, which is weaker than the single P-P bond due to high interelectronic repulsion of the non-bonding electrons.
• In the solid and liquid states, nitrogen is associated through hydrogen bonds, accounting for its higher melting and boiling points than expected.
• The ammonia molecule is trigonal pyramidal with the nitrogen atom at the apex, having three bond pairs and one lone pair of electrons.

Ammonia's Properties and Reactions

• Ammonia gas is highly soluble in water, and its aqueous solution is weakly basic due to the formation of OH- ions.
• Ammonia forms ammonium salts with acids, e.g., NH4Cl, (NH4)2SO4, etc.
• As a weak base, ammonia precipitates the hydroxides (hydrated oxides in case of some metals) of many metals from their salt solutions.
• The presence of a lone pair of electrons on the nitrogen atom of the ammonia molecule makes it a Lewis base.

Preparation of Nitrogen

• Nitrogen can be obtained by the reaction of NH4Cl with NaNO2, followed by purification steps to remove impurities.
• Very pure nitrogen can be obtained by the thermal decomposition of sodium or barium azide.

Properties of Dinitrogen

• Dinitrogen is a colorless, odorless, tasteless, and non-toxic gas.
• Nitrogen has two stable isotopes: 14N and 15N.
• It has a very low solubility in water (23.2 cm3 per liter of water at 273 K and 1 bar pressure) and low freezing and boiling points.
• Dinitrogen is rather inert at room temperature due to the high bond enthalpy of the N≡N bond, but its reactivity increases rapidly with a rise in temperature.