Question #903e4

1 Answer
Mar 20, 2016

Square pyramidal.


In order to be able to determine the molecular geometry of xenon oxytetrafluoride, #"XeOF"_4#, you need to start by drawing its Lewis structure.

To find the number of valence electron you get in one molecule of xenon oxytetrafluoride, add the number of valence electrons of each individual atom that makes up the molecule.

So, xenon oxytetrafluoride will have a total of #42# valence electrons

  • #8# valence electrons are coming from the xenon atom
  • #6# valence electrons are coming from the oxygen atom
  • #7# valence electrons from each of the four fluorine atoms

Now, xenon will be the central atom. It will bond with the oxygen atom via a double bond. This will ensure that oxygen has a complete octet.

The xenon atom will bond with the four fluorine atoms via four single bonds, which will ensure that each of the four fluorine atoms gets a complete octet.

These bonds will account for

#overbrace(1 xx 4)^(color(red)("one double bond")) + overbrace(4 xx 2)^(color(purple)("four single bonds")) = "12 valence e"^(-)#

The remaining #30# valence electrons will be placed as lone pairs - remember that each lone pair of electrons contains two electrons

  • #2# lone pairs on the oxygen atom
  • #3# lone pairs on each of the four fluorine atoms
  • #1# lone pair on the xenon atom

Don't worry about the fact that the xenon atom gets more than eight valence electrons here, it is more than capable of expanding its octet to accommodate these extra electrons.

The molecule's Lewis structure will look like this

Now, molecular geometry depends on the number of regions of electron density that surround the central atom - this is known as the steric number.

Regions of electron density are bonds to other atoms (a single, double, or triple bond counts as one region of electron density) and lone pairs of electrons.

In your case, the xenon atom is surrounded by six regions of electron density

  • a total of five bonds to other atoms
  • one lone pair of electrons

According to VSEPR Theory, a molecule that has a central atom with a steric number equal to six and one lone pair of electrons falls into the #"AX"_5"E"_1# category, i.e its molecular geometry will be square pyramidal.

Indeed, a xenon oxytetrafluoride molecule looks like this