Question

Explain your answer.

7. Which atom or ion is given with an excited outer electron configuration?

(A) Na: 3s^1 (B) B: 2p^3 (C) He: 1s^2 (D) H^-1: 1s^2

9. How many unpaired electrons are there in the Ti^3+ ion?

(A) 0 (B) 2 (C) 1

13. Which set contains three isoelectronic species?

(A) Zn, Cd, Hg (B) Br^+, Kr, Rb^- (C) P^3-, Se^2-, I^- (D) F, Na^+, Mg2^+​

Answer 1

7. (B) B; 9. (C) 1; 13. None of the above

Step-by-step explanation:

7. Excited outer electron configuration

(A) Na: 3s. No.

(B) B: 2p³. Yes.

The ground state electron configuration is 2s²2p, so the two 2s electrons have been excited to the 2p level.

(C) He: 1s². No.

(D) H⁻: 1s². No.

9. Unpaired electrons

Tl: [Ar]4s²3d²

Ti³⁺[Ar]3d

There is one unpaired electron.

13. Isoelectronic species

(A) Zn, Cd, Hg

Zn: [Ar]4s²3d¹⁰

Cd: [Kr]5s²4d¹⁰

Hg: [Xe]6s²4f¹⁴5d¹⁰

Not isoelectronic.

(B) Br⁺, Kr, Rb⁻

Br⁺: [Ar]4s²3d¹⁰4p⁴

Kr: [Kr]

Rb⁻: [Kr]5s²

Not isoelectronic.

(C) P³⁻, Se²⁻, I⁻

P³⁻: [Ar]

Se²⁻: [Kr]

I⁻: [Xe]

Not isoelectronic

(D) F, Na⁺, Mg²⁺

F: [He]2s²2p⁵

Na⁺: [Ne]

Mg²⁺: [Ne]

Two isoelectronic species,

There would be three isoelectronic species if you had F⁻ instead of F.