Question

What characteristics do you expect from an electron-deficient hydride with respect to its structure and chemical reactions? 

Answer 1

An electron-deficient hydride does not have sufficient electrons to form a regular bond in which two electrons are shared by two atoms e.g., B₂H₆, Al₂H₆ etc. These hydrides cannot be represented by conventional Lewis structures. B₂H₆, for example, contains four regular bonds and two three centered-two electron bond. Its structure can be represented as: 

Since these hydrides are electron-deficient, they have a tendency to accept electrons. Hence, they act as Lewis acids.