Question

What is an electron – rich hydrides?

Answer 1

In a stable atom there are a total of eight electrons in the outermost shell of the atom. On the basis of outermost shell electrons, it is concluded that if the compound is electron deficient, electron rich or electron precise compound.

Complete step-by-step answer: Hydrides are compounds or ions which have hydrogen atoms bonded to less electronegative elements. Different types of hydrides are distinguished on the basis of different types of bonds such as ionic, metallic or covalent whereas polymeric hydride is identified on the basis of structure.
We know that there are a total eight electrons in the outermost shell of an atom and these electrons define whether the compound is electron deficient or electron rich.
Electron deficient compounds are those compounds which don’t have sufficient number of electrons for the formation of covalent bonds.
Covalent bond is the bond in which atoms are joined by sharing of electrons. This bond is formed when two atoms share their electrons with each other. In such compounds, central metal atoms don’t have a filled octet. Number of electrons in the outermost shell of such compounds is less than eight.
Group 13 compounds generally form such compounds. Examples of electron deficient compounds of hydrogen are borane and aluminum hydride. These compounds generally exist in polymorphic form.

Note: Polymorphism is defined as the ability of a compound to exist in more than one crystalline form. These forms have different arrangements of the atoms in the structure. Electron deficient compounds exist in polymorphic forms in order to complete their electron deficiency.