what is electron deficiency?

in several books one reads about aluminium and boron in particular being electron deficient and forming unusual forms of hydrides. What exactly is electron deficiency and are other elements of other groups electron-deficient too?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

The concept of "Electron deficiency" is comparing the number of vacant orbitals available in a compound, with the number of electrons available to fill them.

In most compounds, the atoms combine their "valence orbitals" to form molecular "bonding orbitals", and these bonding orbitals are each filled with a pair of electrons.

In "electron deficient" compounds, theoreticians are surprised to find that, if they count up the totals, there's not enough electrons to fill up all the "bonding orbitals" they expect to be there.
.....yet the compounds are still stable and strongly bonded together!
So the theoreticians have to scratch their chins and think up new descriptions of the bonding in these compounds, as they don't seem to follow the same rules as others.

Of course, orbitals are just made up theoretical concepts anyways wink so we shouldn't be too surprised that they don't always seem to work like we expected.

WebElements: the periodic table on the WWW [http://www.webelements.com/]

Copyright 1993-20010 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.