Molecules and Formula unit

Question

some times we are asked to write the equation in particles form. I was wondering what is the difference between molecules and formula unit cause google didn't help.

Answer 1

A formula unit is the lowest whole number ratio of ions represented in an ionic compound. For example: NaCl is the formula unit for sodium chloride, but ,in reality, there are millions of Na's and millions of Cl's in a salt crystal. They are arranged in a crystal lattice. In the case of NaCl, six Na's surround each Cl and six Cl's surround each Na.

A molecule represents a covalent compound such as water. H2O has two hydrogens each bound covalently to the one oxygen.