Molecular Advent Day 21: Salt

who am I to say…

Yet another molecule that you will find on your Christmas dinner (unless you are deprived due to high blood pressure! Mark Wonnacott, Nano Simbox developer, explores this molecule – is it a molecule? Or an ionic compound? Or both? Discuss….


The molecular bonds we usually think of are “covalent”: two atoms each cling tightly to the same electron to form a direct connection that is difficult to break. Salt (or Sodium Chloride), however is made up of atoms connected by “ionic bonds” – the atoms themselves have become charged ions (by the transferring electrons) and are attracted to any oppositely charged atom like a magnet.

Molecules of covalently bonded atoms have a very particular structure, where each bonded pair of atoms share a particular electron between them, but in an ionic compound, all the positive atoms are loosely attracted to all the negative atoms with no atom caring particularly which negatively charged atoms it bonds with.

Water molecules have a positively charged side and a negatively charged side and those sides are just as attractive to ions as ionically bonding with other ions – because of this, water is able to slip between the ionic bonds and separate the ions of the compound from each other – in other words: dissolve it!