Sodium chloride (NaCl) is an ionic compound. We can effectively model it as sodium atoms with one electron removed next to chlorine atoms with one electron added. The attractive force between the positive and negative charges holds the crystal together. If we model the sodium and chlorine ions as point charges separated by 0.28 nm, the spacing in the crystal, what is the magnitude of the attractive force between two adjacent ions

The attractive force between the sodium and chloride ions has a magnitude of -2.94 x 10⁻⁹ N

Explanation:

An electron is a negatively-charged particle. The charge on an electron is -1.6 x 10⁻¹⁹ C. This is also known as the fundamental unit of charge, e. A proton has the same charge as as electron but its charge is positive.

The charge on the chloride ion is negative and is due to an electron whereas the charge on the sodium ion is positive and is due to a proton.

The magnitude of the force of attraction between two charges is given by the Coulomb's law: F = Kq₁q₂/r²

where K is a constant = 9 x 10⁹ N.m₂.C⁻², q₁ = -1.6 x 10⁻¹⁹ C, q₂ = +1.6 x 10⁻¹⁹ C, r = 0.28 nm = 0.28 x 10⁻⁹ m

F = {(9 x 10⁹ N.m₂.C⁻²) (-1.6 x 10⁻¹⁹ C) (+1.6 x 10⁻¹⁹ C)} / (0.28 x 10⁻⁹ m)²

F = -2.94 x 10⁻⁹ N

Therefore, the attractive force between the sodium and chloride ions has a magnitude of -2.94 x 10⁻⁹ N

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