Question

When sodium chloride, `NaCl`, is dissolved in water, the sodium and chloride ions move apart from one another. Why doesn't the sodium then react explosively with the water, like solid sodium metal does?

Answer 1

It is an interesting question. Dissolved single `Na^+` and `Cl^-` ions do not have the same properties as lumps of solid `Na` metal or quantities of `Cl_2` gas.

Explanation:

While it's true that when a crystal of the ionic substance sodium chloride is dissolved in water the sodium and chloride ions separate from one another, they do not separate to form lumps of sodium metal or to form chlorine gas.

Rather, they remain as single `Na^+` and `Cl^-` ions, surrounded by water molecules. Water is a polar substance, and the negative ends of water molecules are attracted to `Na^+` ions and the positive end to `Cl^-` ions.

Ions of a substance do not have the same properties as larger quantities of the substance, which are differently bonded together.

This is an interesting discussion, since solid sodium chloride contains ionic bonds, solid sodium metal contains metallic bonding and chlorine gas contains covalent bonds.

Answer 2

Yes, only when in their pure forms, not when dissolved

Explanation:

When a substance, such as sodium chloride (a.k.a NaCl, table salt) is dissolved, it breaks up into ions, `Na^+`(aq) and `Cl^-`(aq).

The confusion here is that you assume that sodium metal, `Na`(s), which is highly reactive, is the same as its ionized form, `Na^+`(aq). `Na`(s) is a grayish metal that is incredibly reactive, but `Na^+`(aq) is an ion that, when dissolved in water, is not reactive unless added to another substance. The same goes for chlorine: when it is dissolved ionically (`Cl^-`(aq)), it is unreactive unless added to another substance; however, its gaseous form (`Cl_2`(g)) is deadly