Question

(i) Write the electronic configurations of the following ions: (a) H^– (b) Na⁺ (c) O₂^– (d) F^– 
(ii) What are the atomic numbers of elements whose outermost electrons are represented by (a) 3s¹ (b) 2p³ and (c) 3p⁵? 
(iii) Which atoms are indicated by the following configurations? (a) [He] 2s¹ (b) [Ne] 3s² 3p³ (c) [Ar] 4s² 3d¹.

Answer 1

(i) Electronic configurations of given ions:

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(a) H⁻ :

Hydrogen has 1 electron; H⁻ has one extra electron.

Electronic configuration = 1s²

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(b) Na⁺ :

Sodium has atomic number 11; Na⁺ has lost one electron.

Electronic configuration = 1s² 2s² 2p⁶ = [Ne]

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(c) O²⁻ :

Oxygen has atomic number 8; O²⁻ has gained two electrons.

Electronic configuration = 1s² 2s² 2p⁶ = [Ne]

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(d) F⁻ :

Fluorine has atomic number 9; F⁻ has gained one electron.

Electronic configuration = 1s² 2s² 2p⁶ = [Ne]

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(ii) Atomic numbers of elements with given outermost electrons:

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(a) 3s¹ :

Configuration corresponds to sodium.

Atomic number = 11

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(b) 2p³ :

Configuration corresponds to nitrogen.

Atomic number = 7

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(c) 3p⁵ :

Configuration corresponds to chlorine.

Atomic number = 17

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(iii) Atoms indicated by given configurations:

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(a) [He] 2s¹ :

This configuration represents Lithium (Li).

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(b) [Ne] 3s² 3p³ :

This configuration represents Phosphorus (P).

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(c) [Ar] 4s² 3d¹ :

This configuration represents Scandium (Sc).

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Final Answer:

(i) H⁻: 1s², Na⁺: [Ne], O²⁻: [Ne], F⁻: [Ne]
(ii) Atomic numbers: 11, 7, 17
(iii) Elements: Li, P, Sc