1.

(i) Write the electronic configuration of the following ions:(a) He+ (b) Mg2+ (c) O2− (d) S2−(ii) What are the atomic numbers of elements whose outermost electrons are represented by:(a) 3s2 (b) 2p5 and (c) 2s1(iii) which atoms are indicated by the following configurations?(a) [He]2s2 (b) [Ne]3s23p5 (c) [Ar]4s23d5

Answer»

(a) He+Number of electrons = 2 − 1 = 1

\(\therefore\) Electronic configuration = 1s1

(b) Mg2+:Number of electrons = 12 − 2 = 10

\(\therefore\) Electronic configuration = 2,8, = 1s2 , 2s2 , 2p6

(c) O2−:Number or electrons = 8 + 2 = 10

\(\therefore\) Electronic Configuration = 2, 8 = 1s2 , 2s22p6

(d) S2−Number of electrons = 16 + 2 = 18

\(\therefore\) Electronic of Configuration = 2, 8, 8 = 1s2 , 2s22p6 , 3s23p6

(ii) (a) 3s2 , Atomic number of elements = 12

(b) For 2p5 , Atomic number of elements = 9

(c) For 2s1 , Atomic number of elements = 3

(iii) 

ElectronicAtomic No.Atom Configuration
(a) [He]2s24Be
(b) [Ne]3s23p517Cl
(c) [Ar]4s23d525Mn



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