The p-Block Elements

• The p-block elements are placed in groups 13 to 18 of the periodic table
• Their valence shell electronic configuration is ns2np1–6 (except for Helium which has 1s2 configuration)
• The properties of p-block elements are greatly influenced by atomic sizes, ionisation enthalpy, electron gain enthalpy, and electronegativity
• The absence of d-orbitals in the second period and the presence of d or d and f orbitals in heavier elements starting from the third period onwards significantly affect the properties of elements
• The presence of metals, metalloids, and non-metals in p-block elements brings diversification in their chemistry
• Group 15 includes nitrogen, phosphorus, arsenic, antimony, and bismuth
• As we go down the group, there is a shift from non-metallic to metallic through metalloidic character
• Molecular nitrogen comprises 78% by volume of the atmosphere
• Phosphorus occurs in minerals of the apatite family and is an essential constituent of animal and plant matter
• The important atomic and physical properties of Group 15 elements are given in Table 7.1
• The valence shell electronic configuration of Group 15 elements is ns2np3
• Covalent and ionic radii increase in size down the group
• Ionisation enthalpy decreases down the group due to a gradual increase in atomic size
• The electronegativity value decreases down the group with increasing atomic size
• All elements of Group 15 are polyatomic, with dinitrogen being a diatomic gas and others being solids
• Oxidation states of Group 15 elements include -3, +3, and +5
• The common oxidation states of Group 15 elements are -3, +3, and +5
• Nitrogen exhibits +1, +2, +4 oxidation states in addition to -3
• Phosphorus also shows +1 and +4 oxidation states in some oxoacids
• The stability of +5 oxidation state decreases down the group
• Nitrogen has unique properties due to its small size, high electronegativity, high ionisation enthalpy, and non-availability of d orbitals
• Nitrogen has a unique ability to form pπππππ-pπππππ multiple bonds with itself and with other elements like C and O
• Heavier elements of the nitrogen group do not form pπ-pπ bonds due to the large and diffuse nature of their atomic orbitals
• 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 of 941.4 kJ mol-1
• The single N-N bond is weaker than the single P-P bond due to high interelectronic repulsion of non-bonding electrons, resulting in weaker catenation tendency in nitrogen
• Nitrogen's chemistry is affected by the absence of d orbitals in its valence shell, limiting its covalency to four and preventing the formation of dπππππ-pπππππ bonds
• All elements of Group 15 form hydrides of the type EH3 where E = N, P, As, Sb, or Bi, showing gradation in properties with decreasing stability from NH3 to BiH3
• Nitrogen and other elements of Group 15 form two types of oxides: E2O3 and E2O5, with acidic character decreasing down the group
• Group 15 elements react to form two series of halides: EX3 and EX5, with nitrogen not forming pentahalides due to the absence of d orbitals in its valence shell
• All Group 15 elements react with metals to form binary compounds exhibiting -3 oxidation state
• Dinitrogen is produced commercially by liquefaction and fractional distillation of air, and in the laboratory by treating an aqueous solution of ammonium chloride with sodium nitrite
• Dinitrogen is a colourless, odourless, tasteless, and non-toxic gas with low solubility in water 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 with temperature
• Ammonia is obtained from ammonium salts by decomposition with caustic soda or calcium hydroxide, and is manufactured on a large scale by Haber's process
• The main use of dinitrogen is in the manufacture of ammonia and other industrial chemicals containing nitrogen, as well as in providing an inert atmosphere and as a refrigerant
• Dinitrogen combines with hydrogen at about 773 K in the presence of a catalyst (Haber’s Process) to form ammonia: N2(g) + 3H2(g) → 2NH3(g); Δf H° = –46.1 kJmol⁻¹
• Dinitrogen combines with dioxygen only at very high temperature (about 2000 K) to form nitric oxide, NO: N2 + O2(g) → 2NO(g)
• Ammonia is a colourless gas with a pungent odour, and its freezing and boiling points are 198.4 K and 239.7 K respectively
• Ammonia is highly soluble in water and its aqueous solution is weakly basic due to the formation of OH⁻ ions: NH3(g) + H2O(l) → NH4⁺(aq) + OH⁻(aq)
• Ammonia forms ammonium salts with acids and precipitates the hydroxides of many metals from their salt solutions