# Homework Help: Lattice binding energy

1. Sep 18, 2011

### devillenator

1. The problem statement, all variables and given/known data

In a crystal lattice of MgO, the Mg is surrounded by 6 Oxygen atoms as shown.
Assume that the ions all behave as point charges.

If the system behaves as though there were separate interactions between Mg and each of
the Oxygen ions what is the total binding energy of the Mg ion?

2. Relevant equations

$$F_c = -K/a^2$$
$$F=\frac{dE}{da}$$
$$F=F_c+F_R$$

3. The attempt at a solution

so I'm quite confused with this question.

I can find the coulombic force of attraction using $$F_c = -K/a^2$$ if i take a to be the equilibrium bond length and look up values for the ionic radii.

Now that i know the attraction force i can then work out the repulsive force as at the equilibrium bond length the attractive force is balanced by the repulsive force.

my problem is that because the forces balance the net force is zero , so what is the total binding energy of the iron.

2. Sep 20, 2011

### devillenator

would anyone agree that the question is asking for the electron binding energy and that i was trying to find the wrong thing?

im still stuck with this.

Thanks
Sean