Re: How can NaCl dissolve in water? Can Any one explain this phenomenon in molecular level?



newedana wrote:
> NaCl dissolves well in water. No one could explain yet the mechanism of
> dissolving this NaCl in water in molecular level.

NaCl is not a molecular substance. It is an *ionic* substance.

The dissolution is driven by entropy, although enthalpy is a minor but
non-negligible factor.

In the crystal, Na+ ions and Cl- ions occupy positions in a very
regular array. At the surface of the crystal water can bond itself to
the Na+ using the unshared electron pairs on the oxygen atom -
'donated' to the vacant 2p orbitals on sodium. At the surface of the
crystal water can also bond itself to the Cl- using the H+ - 'shared'
between the filled vacant 2p orbitals on Cl- and the filled 1P orbitals
on oxygen.

This 'solvation' process allows the charge on the respective ions to
become distributed over a larger volume of space - the *solvated* ions
rather than the *bare* ions. The reduction of charge density in this
manner dissipates energy. With the Na+ ions and the Cl- ions wrapped
up in water molecules, they cannot return to their original places in
the crystal lattice.

Tom Davidson
Richmond, VA

.

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