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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Winga on August 10, 2005, 08:23:00 AM

Title: LCAO
Post by: Winga on August 10, 2005, 08:23:00 AM

Theoretically, the linear combination of 2 atomic orbitals (left figure) will give 1 bonding & 1 antibonding orbitals in almost same extent of energy.

If a pair of e- occupy the bonding orbital, will it stabilize the bonding orbital?
(right figure)

Title: Re:LCAO
Post by: Mitch on August 10, 2005, 11:28:38 AM

This is one of those questions I know you can answer yourself. Draw a horizontal line anywhere on that chart and make its value worth zero. Then determine the energy before the LCAO and then after, and you tell us which one is lower in energy.

Title: Re:LCAO
Post by: Winga on August 10, 2005, 12:56:43 PM

I am not quite sure what you want me to do, you mean using 10Dq (energy) to calculate?

I just want to know that full filled orbitals are stable than unfilled orbitals, (am I right?) can it apply to this case? If yes, should we draw the bonding orbital (when occupied) at lower position from original postion?

Title: Re:LCAO
Post by: Mitch on August 10, 2005, 01:34:32 PM

Well if you defined the nonbonding orbitals as zero energy. Then you will see that when electrons are put into bonding orbitals that their energy is now lower. Maybe, I don't understand your question?

Title: Re:LCAO
Post by: Winga on August 11, 2005, 04:35:04 AM

I mean...from (fig.1), theoretically, the bonding orbital gains stability and the anti-bonding orbital gains destability in same extent (assume they are the same) comparing with AOs.

My question is, does the bonding orbital gain extra stability when it is filled? (fig.2)

Title: Re:LCAO
Post by: Mitch on August 12, 2005, 02:36:49 AM

I doubt it. You actually loose energy. Its called the pairing energy.