AFMC AFMC Solved Paper-2003

  • question_answer
    Which of the following are iso-structural species?

    A) \[NH_{4}^{+}\]and \[NH_{2}^{-}\]

    B) \[CH_{3}^{-}\]and \[CH_{3}^{+}\]

    C) \[SO_{4}^{2-},PO_{4}^{3-}\]and \[[BF_{4}^{-}]\]

    D) \[NH_{4}^{+}\]and \[N{{H}_{3}}\]

    Correct Answer: C

    Solution :

    Hybridizations on a molecule can be determined as follows\[X=SA+\frac{1}{2}(G-V)X=SA+\frac{1}{2}(G-V+a)\]for simple molecule for polyatomic anions   \[X=SA+\frac{1}{2}(G-V+C)\] for polyatomic cation
    Value of X Hybrid state No. of SA No. of L Shape Type of molecule and example
    2 sp 2 0 Linear \[A{{B}_{2}}:Be{{F}_{2}},\] \[C{{O}_{2}},C{{S}_{2}},NO_{2}^{+}\]
    3 \[s{{p}^{2}}\] 3 0 Trigonal planar \[A{{B}_{3}}:B{{F}_{3}},\] \[AlC{{l}_{3}},S{{O}_{3}},\] \[NO_{3}^{-}CO_{3}^{2-}\]
    2 1 Bent \[A{{B}_{2}}L:S{{O}_{2}},\] \[PbC{{l}_{2}},SnC{{l}_{2}},\] \[NO_{2}^{-}\]
    4 \[S{{P}^{3}}\] 4 0 Tetrahedral \[A{{B}_{4}}:C{{H}_{4}},\] \[SiC{{l}_{4}},SO_{4}^{2-},\] \[ClO_{4}^{-}\]
    3 1 Pyramidal \[A{{B}_{3}}L:N{{H}_{3}},\] \[N{{F}_{3}},P{{H}_{3}},PC{{l}_{5}},\] \[{{H}_{3}}{{O}^{+}}\]
    2 2 Bent \[A{{B}_{2}}{{L}_{2}}:{{H}_{2}}O,\] \[NH_{2}^{-}\]
    4 1 See saw \[A{{B}_{4}}L:S{{F}_{4}},\] \[Te{{F}_{4}}\]
    5 \[s{{p}^{3}}d\] 3 2 T shape \[A{{B}_{2}}{{L}_{2}}:Cl{{F}_{3}},\] \[B{{F}_{3}}\]
    2 3 Linear \[A{{B}_{2}}{{L}_{3}}:Xe{{F}_{2}},\] \[I_{3}^{-},Br_{3}^{-}\]
    6 \[s{{p}^{3}}{{d}^{2}}\] 5 1 Square pyramid \[A{{B}_{5}}L:I{{F}_{5}},\] \[Br{{F}_{5}}\]
    4 2 Square planar \[A{{B}_{4}}{{L}_{2}}:Xe{{F}_{4}}\]
    SA = number of atoms or groups around central atom G = valence electrons of central atom V= valency of central atom (number of mono valent atoms or \[2\,\,\times \] number of divalent atoms etc.) a and c = charge on anion and cation respectively (A = central atom B = SA, L = lone pair) \[SO_{4}^{2-},PO_{4}^{3-},BF_{4}^{-}\] have same number of bond electrons have same hybridisation \[s{{p}^{3}}\] so are isostructural (tetrahedral)


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