Electron rich hydrides have excess electrons that are present as lone pair. A pair of electrons occupying an orbital in an atom or molecule and not directly involved in bonding is called as lone pair of that atom. For example, Nitrogen has 5 electrons in its valence shell, therefore its valency is 3. Nitrogen forms a covalent bond which is formed by sharing of electrons. It will share 3 electrons with another atom and 2 electrons will remain in its valence shell. The remaining 2 electrons are its lone pair.