How Can I Calculate Exact Bond Energy for S and P Orbitals?

[pixelpuffin]

I need some maths for a program to determine the exact (or as close as it can be mathed) bond energy of bonds from the first two rows of the periodic table S and P orbitals
all the websites I can find tell you what the average bond energy for a specific common bond is but that won't do for these maths
wikipedia says "bond energy: requires lengthy calculations, even for the simplest bonds"
but wikipedia doesn't have any of the lengthy math there
either how this is calculated or a link to such calculations would be much appreciated

 

[DrDu]

These calculations require the approximate solution of the Schroedinger equation for the electrons of the molecule in question and are far to complicated to be done by hand. There are many dedicated quantum chemistry programs available to do this kind of calculations. Maybe accurate bond energies can be most easily be obtained using density functional theory programs.
see e.g.,
http://en.wikipedia.org/wiki/Density_functional_theory

 

[pixelpuffin]

I would like to simplify the equation as far as I can to get the average strength of any given bong in kj/mol
would it be inaccurate to say that for example any hydrogen carbon bond in which one of the carbons other orbitals is taken by one other atom is of a constant energy
if not why so
if so this would require only that i know the bond energy of hydrogen carbon when one other orbital is filled and thusly any given bond in which a defined number of bonds are filled would have the same result every time (unless my random example happened to be a strange exception to a common rule)