Inorganic chem

• Group 15 Elements


  • Nitrogen
  • Phosphorus
  • Arsenic
  • Antimony
  • Bismuth

  
• Pnicogens


  Group 15 elements and their compounds
• Group 15 Elements


  • Valence shell electronic configuration is ns2 np3
  • Nitrogen and phosphorus are non-metals, arsenic and antimony are metalloids, bismuth is a metal
  • Nitrogen is a diatomic gas, all other elements are solids
  • Nitrogen is diatomic, others are tetratomic
  • Melting point increases from nitrogen to arsenic, boiling point increases down the group
  • Density increases down the group
  • Atomic radii increases down the group
  • All except bismuth exhibit allotropy

  
• Oxidation state


  The total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom
• Stability of +3 oxidation state

  Increases down the group due to inert pair effect
• Stability of +5 oxidation state

  Decreases down the group due to inert pair effect
• Ionization enthalpy


  Ionization energy of nitrogen is very high due to its small size and half-filled highly stable configuration. Decreases down the group.
• Electronegativity


  Decreases from nitrogen to bismuth
• Catenation


  The self-linking of atoms of an element to form chains and rings. Group 15 elements exhibit this property to a lesser extent than group 14 elements due to weaker E-E bonds.

  
• Reactivity of elemental nitrogen

  Highly unreactive due to its strong triple bond, almost as inert as noble gases
• Reactivity of white phosphorus

  Extremely reactive, kept in water, inflammable, can be ignited at 45°C
• Properties of group 15 hydrides (EH3)

  • Thermal stability
  • Basic strength
  • Solubility in water
  • Bond angle
  • Strength of M-H bond

  
• Properties of group 15 hydrides


  NH3 < PH3 < AsH3 < SbH3 < BiH3 (Reducing character, covalent character, rate of combustion)

  
• Trihalides of group 15 elements

  Behave as Lewis acids, order of strength is PCl3 > AsCl3 > SbCl3

  
• Trihalides of nitrogen


  Behave as Lewis bases, order of strength is NF3 < NCl3 < NBr3 < NI3

  
• NCl3 is an explosive compound
• Acidic strength of group 15 pentoxides and trioxides

  Decreases on moving down the group: N2O5 > P2O5 > As2O5 > Sb2O5
• BiOCl is called pearl white
• Preparation of dinitrogen (N2)


  1. Heating ammonium dichromate

  2. Heating sodium azide

  3. Heating barium azide

  
• Reaction of nitrogen with alkali metals


  Does not react with alkali metals except lithium, reacts with alkaline earth metals to give metal nitrides

  
• Reaction of nitrogen with oxygen

  1. Nitrogen burns in oxygen to form nitric oxide

  2. Nitric oxide reacts with more oxygen to form nitrogen dioxide
• Reaction of nitrogen with non-metals

  1. Reacts with hydrogen to form ammonia

  2. Reacts with carbon to form cyanides
• Reaction of nitrogen with calcium carbide

  Calcium cyanamide is formed

  
• Uses of dinitrogen (N2)

  Liquid nitrogen is used as a refrigerant, used in manufacture of nitric acid, ammonia, calcium cyanamide and other nitrogenous compounds, used for filling electric bulbs
• Laboratory preparation of ammonia (NH3)

  Heating ammonium chloride with calcium hydroxide

  
• Industrial preparation of ammonia (NH3) - Haber process


  Nitrogen and hydrogen react at high temperature and pressure in the presence of an iron catalyst
• Properties of ammonia (NH3)

  Colourless gas with pungent odour, extremely soluble in water due to hydrogen bonding, strong Lewis base
• Reaction of ammonia with chlorine

  1. When ammonia is in excess, nitrogen is the main product

  2. When chlorine is in excess, nitrogen trichloride is the main product
• Reaction of ammonia with Nessler's reagent

  Forms a brown precipitate
• Uses of ammonia (NH3)

  Used as a refrigerant, used to produce various nitrogenous fertilizers
• Oxides of nitrogen


  • Nitric oxide (NO)
  • Nitrogen dioxide (NO2)
  • Dinitrogen trioxide (N2O3)
  • Dinitrogen tetroxide (N2O4)
  • Dinitrogen pentoxide (N2O5)

  
• NO2 contains an odd number of valence electrons, on dimerization it is converted to the stable N2O4 molecule with an even number of electrons
• Laboratory preparation of nitric acid (HNO3)

  Reaction of sodium nitrate with concentrated sulfuric acid

  
• Industrial preparation of nitric acid (HNO3) - Ostwald process

  Oxidation of ammonia to nitric oxide, then further oxidation and absorption in water

  
• Physical properties of nitric acid (HNO3)

  Syrupy, colourless, pungent liquid, usually available as 68% and 15.7 M aqueous solution, often yellow due to small concentrations of NO2

  
• Reaction of nitric acid with zinc under different conditions

  1. With excess nitric acid, hydrogen is evolved and zinc nitrate is formed

  2. With dilute nitric acid, zinc dissolves to form zinc nitrate and hydrogen

  
• Reaction of nitric acid with copper under different conditions

  1. With excess nitric acid, nitrogen dioxide is formed

  2. With dilute nitric acid, copper dissolves to form copper nitrate and nitrogen monoxide

  
• Reaction of nitric acid with non-metals

  Reacts with phosphorus to form phosphoric acid, reacts with sulfur to form sulfuric acid
• Brown ring test for nitrates


  Nitrate ion reacts with iron(II) sulfate and sulfuric acid to form a brown ring

  
• Metals like iron, chromium, nickel, aluminum or cobalt become passive or inactive due to the formation of stable oxide layers