Long Answer TypeWhat do you understand by:
(i) electron deficient
(ii) electron-precise and
(iii) electron rich compounds of hydrogen?
Provide justification with suitable examples.
Electron deficient compounds. Hydrides of group 13 (i.e. BH3, AlH3etc.) have lesser electrons to form normal covalent bonds and hence are called electron deficient hydrides. To make up this deficiency, these hydrides generally exist in polymeric forms such as B2H6, B4H10, (AlH3)n etc. They act as Lewis acids i.e. electron acceptors.
(ii) Electron-precise compounds. Electron precise compounds have the required number of electrons to write their conventional Lewis structures. All elements of group 14 form such compounds (i.e. CH4, SiH4, GeH4, SnH4, PbH4), which are tetrahedral in geometry. They do not act as Lewis acids or Lewis bases.
(iii) Electron rich compounds. Electron rich hydrides have excess electrons which are present as lone pairs. Elements of group 15, 16, 17 form such compounds (NH3, PH3, H2O, H2S, HF, HCl etc.). They all behave as Lewis bases i.e. electron donors.
Short Answer TypeWhat characteristics do you expect from an electron-deficient hydride with respect to its structure and chemical reactivity ?
Long Answer TypeWhat do you understand by the term ‘non-stoichiometic hydrides’? Do you expect this type of hydrides to be formed by alkali metals?
Short Answer TypeSaline hydrides are known to react with water violently producing fire. Can CO2, a well-known fire extinguisher, be used in this case? Explain.
What do you expect the nature of hydrides if formed by elements of atomic numbers 15, 19, 23, 44 with dry dihydrogen? Compare their behaviour towards water.
Can Phosphorus with outer electronic configuration 3s23p3 form PH5?
Or
P forms PH3 but not PH5. Comment.
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