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What are electron deficient compounds ? Are BCl_(3) and SiCl_(4) electronsdeficient species ? Explain |
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Answer» Solution :Species in which the central atom eitherdoes not have eight electrons in the valence shell or those which have 8 electronsin the valenceshell but can EXPAND their covalency beyond 4 due to the PRESENCE of d-orbitals, are called electron deficientmolecules. For EXAMPLE. (i) In `BCl_(3)`, the centralboron atom has only six electrons. Therefore, it is an electrons deficient compound. As such, it ACCEPTS a pair of electrons from `NH_(3)` to form an adduct  (ii) In `SiCl_(4)`, the central Si atom has 8 electrons but it can expandits covalency beyond 4 due to the presenceof vacant d-orbitals. Thereforein principle, `SiCl_(4)` shouldalso be an electron-deficient molecule but, in fact it does not accept two more `Cl^(-)` ions to form `[SiCl_(6)]^(2-)` becauseof the following two reasons. (i) Six large sized `Cl` atoms cannot be accommodated AROUND small `Si` atom. (ii) Due to bigger size of `Cl`, interaction betweenlone pairs of chlorine atom and the empty d-orbitals silicon atom is weak. |
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