The water is a lot of H2O molecules with the H's being positively charged and the O's being negatively charged. When you add salt to water it is also negatively charged on one end and positively charged on the other end. The Na is positive and the Cl is negative because the Cl has a much higher electronegativity and so it gets the electrons. So the H2Os go and grab salt molecules and runs off with them. The H's grab the Cl's and the O's gran the Na's and it pulls the solid salt apart.
Why is the freezing point lowered when salt is added to water?
The freezing point is lowered because the heat is being put into the salt molecules so the water can pull them apart. With the higher heat the salt is pulling, the freezing point goes down because you need it to get colder with the salt pulling in more heat. So because the salt is pulling in more heat and moving the molecules faster it causes melting to happen more than freezing. So had I had my water at exactly 32 F and put and ice cube in it it would stay the same size because the water is freezing and the ice is melting at the same rate. If you add salt though then the salt brings in heat and it begins to melt faster than freeze, so with salt the freezing point goes down because with salt it can't freeze as fast because the salt is busy keeping it warm.
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