لاعضوية

• The Sixth lecture, 2023/2024, Pro. Dr. Mohammed Hamid
• Elements of Group VA or 15

  • Nitrogen (N)
  • Phosphorus (P)
  • Arsenic (As)
  • Antimony (Sb)
  • Bismuth (Bi)
  • Ununpentium (Uup)

  
• Pnictogens


  The collective name for the elements of Group VA or 15
• Group VA or 15 elements

  • P-block elements
  • Last differentiating electron is accommodated on np shell
  • Have five electrons in the valency shell
• Ununpentium (115) is a recently discovered synthetic and radioactive element with very little known about its properties
• Electronic configuration of Group VA elements

  • ns^2 np^3 configuration

  1. orbital is paired and three p-orbitals are unpaired
• The penultimate shell is saturated in N, P, As but unsaturated in Sb and Bi
• Elements of Group VA are fairly stable and not so reactive due to their half-filled orbitals
• Physical properties that show gradation in Group VA

  • Metallic and non-metallic character

  Physical state

  Atomic radii

  Ionisation energy

  Electronegativity

  Density

  Allotropy
• Catenation in Group VA elements

  • N, P and As exhibit catenation but less than Group IVA elements

  Bond energies decrease from N-N to P-P to As-As
• Atomicity of Group VA elements

  N2 is diatomic due to multiple bonding

  P4, As4, Sb4 are tetrahedral molecules due to repulsion between non-bonded electrons
• Oxidation states of Group VA elements

  • +5, +3

  Tendency for +3 state increases and +5 state decreases from N to Bi

  N and P also show -3 oxidation state
• Nitrogen exhibits a wide range of oxidation states from -3 to +5

  
• Disproportionation is shown by intermediate oxidation states of N and P in acidic medium
• Valency and bonding in Group VA elements

  Form 3 covalent bonds to achieve stable configuration

  Sb and Bi can form M^3+ ions but are not very stable

  N forms multiple bonds easily, other elements show reluctance

  N has max covalency of 4, other elements can show 5 or 6 due to d-orbitals
• Thermal and electrical conductivity increase down the group due to increased delocalization of electrons
• Occurrence of Group VA elements

  • N: Free in atmosphere, combined in nitrates, proteins, etc.

  1. Not free, 11th most abundant in Earth's crust, in DNA, RNA, ATP, etc.

  As, Sb, Bi: Not abundant, occur as sulphides or oxides

  
• Chemical properties of Group VA elements

  • N is chemically inert due to stable triple bond

  P is highly reactive, heavier elements are less reactive

  Oxides show decreasing acidity from N to Bi
• Oxides formed by elements of group 15

  • X2O3
  • X2O4
  • X3O5

  
• Relationship between electronegativity and acidic character of oxides

  Greater the electronegativity, more the acidic character of the oxide
• Relationship between oxidation state and acidic character of oxides


  Higher the oxidation state, greater the acidic character
• Other oxides formed by nitrogen

  • N2O
  • NO

  
• Bismuth forms bismuth monoxide (BiO)
• Acidic nature of group 15 oxides

  • N2O3 and P2O3 are acidic
  • As2O3 and Sb2O3 are amphoteric
  • Bi2O3 is more basic and less acidic

  
• Bi2O3 shows feeble acidic character as it slightly dissolves in concentrated NaOH solution

  
• Reaction of Bi2O3 with NaOH

  Bi2O3 + 6NaOH → 2Na3BiO3 + 3H2O

  
• Sodium bismuthite


  Product of the reaction of Bi2O3 with NaOH

  
• Acidic nature of group 15 pentoxides


  • N2O5, P2O5 and As2O5 are soluble in water and form acids
  • Sb2O5 and Bi2O5 are insoluble in water but dissolve in alkalies

  
• Acidic nature of group 15 M2O4 oxides


  • N2O4 is most acidic
  • Acidic nature decreases from N to Bi
• Reason for decrease in acidic nature of group 15 oxides from N to Bi


  Decrease in nonmetallic character and increase in metallic character from N to Bi
• In oxides of a particular element, the acidic nature increases as the percentage of oxygen increases or as the oxidation state increases
• H3PO4 is stronger than H3PO3
• Thermal stability of group 15 oxides decreases with increasing atomic number
• Thermal stability of group 15 oxides

  • N2O3 is most stable
  • N2O5 is less stable
  • P2O5 is thermally stable
  • As2O5 and Sb2O5 are less stable
  • Bi2O5 is least stable
• Except P2O5, all the pentoxides show oxidising properties
• N2O5 is the strongest oxidising agent
• Oxides of nitrogen


  • They are structurally different from the oxides of the rest of the group 15 elements
  • This is due to nitrogen's ability to form pπ-pπ multiple bonds which are present in its oxides
  • The rest of the elements do not form multiple bonds and prefer to form cage structures for their oxides

  
• Oxyacids formed by group 15 elements

  • Nitrous acid (HNO2)
  • Nitric acid (HNO3)
  • Hypophosphorous acid (H3PO2)
  • Phosphorous acid (H3PO3)
  • Hypophosphoric acid (H4P2O4)
  • Orthophosphoric acid (H3PO4)
  • Metaphosphoric acid (HPO3)
  • Pyrophosphoric acid (H4P2O7)
  • Arsenious acid (H3AsO3)
  • Arsenic acid (H3AsO4)
  • Antimony oxyacid (H3SbO3)
  • Meta-bismuthic acid (HBiO3)

  
• Strength and stability of group 15 oxyacids


  Decreases gradually with decrease in electronegativity of central atom
• Strength of group 15 oxyacids

  • HNO3 (Strong)
  • H3PO4 (Weak)
  • H3AsO4 (Very weak)
  • H3SbO4 (Weakest)