Molecular Structure

[Lauren Huang 1H]

If the two lone pairs of Xe in XeF4 are placed opposite each other due to electron repulsion, why is it that the two lone pairs in H20 are placed next to each other?

[yea-lyn pak_1G]

H20 only has four regions of electron density, whereas XeF4 has six regions of electron density. So when drawing the VSEPR model for XeF4, you would start out by drawing the fluorines symmetrically about Xe. Then, when you think about the placing of the two lone pairs of electrons, the most stable placement would be for them to be axial (placed opposite each other). For H20, the lone pairs look like they're next to each other on paper, but if you think about it in a 3D state, one of the hydrogens and the two lone pairs are placed symmetrically around the oxygen, creating a pyramid-like structure.