Based on "I Believe in Father Christmas" by Greg Lake
In memory of the moment in my second year when this all made sense -

and dedicated to my Dad, who looks to the sky with excited eyes every Christmas




SF6 has twelve electrons -
Its bonds are sp3d.
But how can d-orbitals bond, if
They're so high in energy?
(I remember those Sixth Form textbooks
Where bonds are bonds, with two electrons shared:
Things are what they are by VSEPR
And you just blame it all on lone pairs.)

They sold me a cubic point group -
They sold me two e1gs:
They're occupied, and non-bonding
And from the fluorine SALCs.
And I believed in MO theory,
As I saw the bond order was less than one -
And the molecule swam through MO diagrams
With three-centre-four-electron bonds.

Eight e in four bonding MOs -
t1u and a1g -
e1g can't overlap, 'cos
Nothing on S has the same symmetry.
SF6 is hypervalent -
The "lone pairs" are ligand-based -
Electron density is okay on fluorine*,
So it all works out, just the same.

*Because it's electronegative - but I just couldn't get that into the song!



© Aimee Hartnell, December 2001