Ancient Warmth
Ancient Warmth

Quick Science Lesson

Published 2021-03-31. Last modified 2021-01-22.
Time to read: about 2 minutes.

How Do Salts Dissolve?

The atomic structure of salt crystals form a lattice, which is composed of alternating positive and negative ions.

Sodium (Na) and chlorine (Cl) ions that make up table salt, neatly arranged as a crystal lattice.
Sodium (Na) and chlorine (Cl) ions that make up table salt, neatly arranged as a crystal lattice.

Water dissolves ionic compounds such as salts, partly because water is a polar molecule. Polar molecules have an asymmetric geometry, which causes them to have an uneven electric charge around them.

A water molecule, showing its polar charges: a negative charge from the oxygen atom in the middle (shown in red), and two hydrogen atoms with positive charges at the ends (shown in blue).
A water molecule, showing its polar charges: a negative charge from the oxygen atom in the middle (shown in red), and two hydrogen atoms with positive charges at the ends (shown in blue).

When a crystal of salt is placed in water, the water molecules collide with the salt’s crystal lattice. Water is attracted to the sodium chloride ions in the crystal lattice because water molecules have positively charged and a negatively charged regions. The positively charged sodium ions in the crystal attract the oxygen ion in water molecules, which are negatively charged. The negatively charged chloride ions in the crystal attract the hydrogen ends of the water molecules because they are positively charged.

When salt dissolves, its ions become surrounded by water molecules. As water molecules bump into the salt’s ions, the crystal lattice starts coming apart.

After coming apart from the salt crystal, the individual Na and Cl ions are surrounded by water molecules. The individual sodium (Na+) ions are surrounded by water molecules with the oxygen atom oriented near the positive ion. Likewise, the chloride (Cl-) ions are surrounded by the hydrogen ions in water molecules, which have the opposite charge.

Salt completely dissolved in water. No salt crystals remain.
Salt completely dissolved in water. No salt crystals remain.

Portions of this section were based on CC licensed material published by Chemistry Concepts Intermediate.
Authored by: Calbreath, Baxter, et al..
Provided by: CK12.org.
Located at: http://www.ck12.org/book/CK-12-Chemistry-Concepts-Intermediate/.
License: CC BY-NC: Attribution-NonCommercial

Elements That Make Water Hard

Hard water ions come from groups 1 through 12 on the period table of elements.

The rounded rectangle encloses all of the elements that make water hard when they dissolve. The arrows point to elements Mg (magnesium) and Ca (calcium). Other elements within the rounded rectangle can also make water hard; for example, Fe (iron) and Na (sodium) are found in water from some areas.

Period table of the elements, modified from Encyclopedia Britannica online.
Period table of the elements, modified from Encyclopedia Britannica online.