Re: Questions about Highschool chemistry

Posted by Uncle Al on Feb 03, 2004 at 19:49

Re: Questions about Highschool chemistry (RG)

To a first approximation, put the lone pairs as far from each other as possible, then put in the bonds. You have 4 electrons left over or two lone pairs, plus four Xe-F bonds to make six total orbital lobes. A good first guess is an octahedral coordination sphere.

Put Xe at the center of the octahedron. Put the two lone pairs at opposite apices. Now the four fluorines form a square-planar array at the equator, which is correct for XeF4.

XeF6 is a nasty beast. It has a stereoactive lone pair and six fluorines to give a pseudo 7-coordinate structure that is fluxional (constantly rearragnes to give iitelf back with atom positions scrambled.

There are more sophisticated treatments that have better predictive power in nasty and complex cases.

Uncle Al
(Do something naughty to physics)

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