Molecules are specified through Lewis structures, a diagram showing the arrangement of valence electrons among the atoms in a molecule. A valence electron is an electron present in the outermost energy level of an atom. So, if you were to draw out the Lewis Structure of two hydrogens, it would simply be H:H (because each hydrogen atom has one valence 1s). The Lewis Structure for Hydrogen Chloride would be

because chlorine has 7 valence electrons, and hydrogen only has one. However, there are many variations among Lewis Structures, and no one has a correct format.

        There is also the task of naming molecular compounds. This is relatively simple because there is just a lot of prefixes, roots, and suffixes to use. For the number of atoms there are, you match it to its prefix. For example, you can take P2O3. The prefixes used for this is di (2) and tri (3), so you would read it, diphosphorus trioxide.         

This is a picture of Gilbert Newton Lewis, the creator of the Lewis Structure.

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  How do ionic and covalent bonds compare?

  How do you name salts?

  What is a polyatomic ion?