# Why does water break salt really

A kid asked me this question just the other day, and I said that the positive part of $\ce{H2O}$ attracts the negative $\ce{Cl}$ ion and the negative part of the $\ce{H2O}$ attracts the positive Na ion.

Then he asked me several questions which stumped me:

1. Why doesn't $\ce{NaCl}$ dissolve water instead (break water into $\ce{H}$ and $\ce{O}$)?
2. If $\ce{H2O}$ is electrically neural, why would it attract any ions?
3. Why doesn't $\ce{NaCl}$ stick together, how can one know if one molecule will attract the ions hard enough that the ions breaks away?
4. Why is Na positive and $\ce{Cl}$ negative?

Hopefully someone can help me answer the above questions as I have not done chemistry in years!

The main reason about why water breaks salt is related to the relative permittivity $\epsilon_r$ of water compared to its value in air. In fact,$\epsilon_r= 80$ in water, while its value in air is $\epsilon_r= 1$. Now, if we look at the formula of the Coulomb force, which is responsible of the electrostatic attraction between ${\rm Na}^+$ and ${\rm Cl}^-$ : $$f = \frac{q.q'}{4\pi \epsilon_0\epsilon_r r^2}$$ (Where q and q' are the charges of ${\rm Na}^+$ and ${\rm Cl}^-$, and r is the distance between the two punctual charges).