1.

(a) [BeF_(4)]^(2-) exits, but [BeCl_(6)]^(4-) does not. Give reson. (b). Hydrated beryllium ion exists as [Be(H_(2)O)_(4)]^(2+), whereas hydrated magnesium ion exists as [Mg(H_(2)O)_(6)]^(2+). Give reason.

Answer» <html><body><p></p>Solution :a. `[BeF_(4)]^(2-)` <a href="https://interviewquestions.tuteehub.com/tag/exists-979838" style="font-weight:bold;" target="_blank" title="Click to know more about EXISTS">EXISTS</a>, but `[BeF_(6)]^(4-)` does not. This can be explained on the basis of valence <a href="https://interviewquestions.tuteehub.com/tag/electronic-968847" style="font-weight:bold;" target="_blank" title="Click to know more about ELECTRONIC">ELECTRONIC</a> configuration: <br/> <img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/KSV_INORG_CHM_P1_C05_S01_008_S01.png" width="80%"/> <br/> <a href="https://interviewquestions.tuteehub.com/tag/due-433472" style="font-weight:bold;" target="_blank" title="Click to know more about DUE">DUE</a> to the absence of low-lying `d`-orbitals in beryllium, it cannot expand its coordination number beyond`4`, hence `[BeF_(4)]^(2-)` exists, but `[BeF_(6)]^(4-)` does not.<br/> b. Hydrated beryllium ion exists as `[Be(H_(2)O)_(4)]^(2+)`. <br/> <img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/KSV_INORG_CHM_P1_C05_S01_008_S02.png" width="80%"/> <br/>Due to the presence of only four orbitals of equivalent energy in `Be^(2+)` ion and due to the absence of low-lying `d-`orbitals in `Be^(2+)` ion, it can coordinate with four water molecules only, hence hydrated beryllium ion exists as `[Be(H_(2)O)_(4)]^(2+)`. <br/> Whereas in case of <a href="https://interviewquestions.tuteehub.com/tag/magnesium-1082716" style="font-weight:bold;" target="_blank" title="Click to know more about MAGNESIUM">MAGNESIUM</a>, due to the availability of low-lying d-orbitals of <a href="https://interviewquestions.tuteehub.com/tag/suitable-633281" style="font-weight:bold;" target="_blank" title="Click to know more about SUITABLE">SUITABLE</a> energy, `Mg` can expand its coordination number to 6 <br/> <img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/KSV_INORG_CHM_P1_C05_S01_008_S03.png" width="80%"/><br/> Hence, hydrated magnesium ion exists as `[Mg(H_(2)O_(6))]^(2+)`</body></html>


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