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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: AllAmericanBreakfast on October 20, 2018, 04:16:44 PM

Title: Why don't salt crystals stick back together?
Post by: AllAmericanBreakfast on October 20, 2018, 04:16:44 PM

Given what I understand of the lattice structure of ionic compounds, it seems like table salt crystals should all stick back together in the salt shaker. After all, they still have that charge along the outer edge, and they're held together by electromagnetic forces, right?

I know that humidity does cause salt to stick back together. But why don't they do it on their own, even in a vacuum?

Title: Re: Why don't salt crystals stick back together?
Post by: Enthalpy on October 23, 2018, 08:41:15 AM

Welcome, AllAmericanBreakfast!

Part of the answer is that the surfaces of the crystals don't match an other due to irregular shape, so just very few chemical bonds can establish simultaneously.

An other part of the answer is that no surface is clean because they're too reactive for that. Within our atmosphere, a new surface (made for instance by breaking a crystal) reacts in nanoseconds and covers itself with a complicated and ill-defined layer, several molecules thick, of oxides, hydroxides, carbonates and more exotic things. When you approach two crystals, it's already too late to establish the strong chemical bonds: the surfaces are "passivated".

I must forget a few dozen reasons more.