question_answer 42)

(i) Write down the electronic configurations of the following ions: (a) \[{{H}^{-}}\] (b) \[N{{a}^{+}}\] (c) \[{{O}^{2-}}\] (d) \[{{F}^{-}}\]

Answer:

(a) \[H(l{{e}^{-}})\to 1{{s}^{1}}\] \[{{H}^{-}}(2{{e}^{-}})\to 1{{s}^{2}}\] (b) \[Na(1\,1{{e}^{-}})\to 1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{1}}\] \[N{{a}^{+}}(10\,{{e}^{-}})\to 1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{1}}\] (c) \[{{O}^{2-}}(8{{e}^{-}})\to 1{{s}^{2}},2{{s}^{2}},2{{p}^{4}}\] \[{{O}^{2-}}(10{{e}^{-}})\to 1{{s}^{2}},2{{s}^{2}},2{{p}^{6}}\] (d) \[F(9{{e}^{-}})\to 1{{s}^{2}},2{{s}^{2}},2{{p}^{5}}\] \[{{F}^{-}}(10{{e}^{-}})\to 1{{s}^{2}},2{{s}^{2}}2{{p}^{6}}\] (ii) What are the atomic numbers of the elements whose outermost electrons are represented by: (a) \[3{{s}^{1}}\] (b) \[2{{p}^{3}}\] (c) \[3{{d}^{6}}\] Sol: (a) Configuration of element: \[1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{1}}\] Total electrons = 11 Atomic number =11 (b) Configuration of element: \[1{{s}^{2}},2{{s}^{2}},2{{p}^{3}}\] Total number of electrons =7 Atomic number = 7 (c) Configuration of the element: \[1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}},3{{p}^{6}},3{{d}^{6}}.4{{s}^{2}}\] Total number of electrons = 26 \[\therefore \] Atomic number = 26 Note: In a neutral atom, number of electrons and protons are same. Therefore, atomic number will be equal to the number of electrons. (iii) What atoms are represented by the following configurations? (a) \[[He]2{{s}^{1}}\] (b) \[[Ne]3{{s}^{2}}3{{p}^{3}}\] (c) \[[Ar]4{{s}^{2}}3{{d}^{1}}\] Sol: (a) Configuration: \[[He]2{{s}^{2}}\] Atomic number = \[2+1=3\] Element = Lithium (Li) (b) Configuration: \[[Ne]3{{s}^{2}}3{{p}^{3}}\] Atomic number = 10 + 5 = 15 Element = Phosphorus (P) (c) Configuration: \[[Ar]4{{s}^{2}}3{{d}^{1}}\] Atomic number = 21 Element = Scandium (Sc)