Re: Rationalize the statement that SF4 has bond angles of 179 and 103 degrees

Date: Tue Feb 27 04:23:25 2001
Posted By: Sean Hunt, Secondary School Teacher, Science, ISM
Area of science: Chemistry
ID: 982991641.Ch

Message:

Dear Sabrina,

Thank you for contacting the MadSci Network. I will try to answer your question but please refer to the website for Sheffield University’s School of Chemistry. The subject area is Valence Shell Electron Pair Repulsion Theory (VSEPR).

SF4 has sulphur as its central atom.
The sulphur has 6 electrons in its outer shell (6 valence electrons)
Each fluorine atom contributes 1 electron giving a total of a
Adding these two values gives 10 electrons or 5 electron pairs.
This gives a geometry of trigonal bipyramidal.
The angles in this shape are therefore 180 degrees and 120 degrees. See diagram of this shape.

With SF4 one of the electron pairs is not involved in bonding (lone pair). VSEPR predicts that a lone pair will repel bond pairs more than bond pairs repel bond pairs, therefore the bonds will be pushed slightly out of shape, changing the angles to 179 degrees and 103 degrees respectively. It is difficult to predict these angles precisely but you can guess. I hope this helps to answer your question. You should look at drawings or models when studying this subject area.(see the website above) Good luck with your studies.

Sean Hunt
Teacher of Science (ISM,Tanzania)

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