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## Homework Statement

Calculate the attractive force between a pair of Cu

^{2+}and O

^{2-}ions in the ceramic CuO that has an interatomic separation of 200pm.

## Homework Equations

[itex]E_A= -\frac{(z_1\cdot e)(z_2\cdot e)}{4\pi\cdot\epsilon_o\cdot r}[/itex]

Where z_1 and z_2 are the valences of the two ion types, e is the charge of an electron (1.602 * 10^-19 C), epsilon_o is the permittivity of a vacuum (8.85*10^-12 F/m), and r is the distance between the two ions.

[itex]E_n=\frac{m\cdot e^4 \cdot z^2}{2n^2 \cdot \hbar^2}[/itex]

Where m= mass of electron, z= atomic number, e= charge of an electron, n is the energy level.

## The Attempt at a Solution

The problem is that I don't know how to find z_1 and z_2. Do I use [itex]E_n=\frac{m\cdot e^4 \cdot z^2}{2n^2 \cdot \hbar^2}[/itex] to find the energy in the valence electrons? The problem is that I don't know how to use that equation because when I plug in what I think I should for the variables it gives me an answer with units all wrong... Here's an example from another problem where I tried to use that equation...

plugging in 1 for n, 3 for z, 9.11*10^-31 kg for m, -1.602*10^-19 Coulombs for e, and 1.054572×10^-34 J*s for h, we get

E_1= ((9.11*10^-31 kg))*((-1.602*10^-19 C)^4)*(3^2)/(2(1.054572×10^-34 J s)^2) = 2.428×10^-37 s^6A^4/(kg m^4) (second to the 6 amperes to the fourth per kilogram meter to the fourth).

So what to do?