Question

The energy-separation curve for two atoms, a distance, r, apart is: U(r)=−A/r^m+B/r^n

Derive and expression for the stiffness of the bond at the equilibrium spacing, in terms of A, B, m, n, and r0.
S=dF/dr at r=r0:


This is wrong answer for S:
Am/r^(m+1) - Bn/r^(n+1)

Answer 1

still looking for what F is.

Answer 2

F is dU/dr, but can't be "r" in answer, only A, B, m, n and r0

Answer 3

Well, if F is dU/dr, and U is a function of r, then there will certainly be r in the answer.

But, you want F(r) at r=r0, so geez, just plug in r0!

Am/r0^(m+1) - Bn/r0^(n+1)

There are other ways of expressing that, but that's another exercise.

Answer 4

I tried this yesterday and doesn't work