What is #"molecularity"#? And how does #"molecularity"# relate to the melting point/boiling point of a substance?

1 Answer
Nov 10, 2015

Melting points and boiling points are (generally) a good indication of the molecularity of an element.


So what is molecularity? It describes whether the element in question is a discrete molecule or exists as non-molecular species. Metals exhibit metallic bonding, in which there are no discrete molecules, and each metal atom contributes 1 or more of its valence electrons to an electron sea that is presumed to give rise to metallic properties: conductivity to heat and electricity; malleability; and ductility.

On the other hand, network covalent solids, such as diamond or graphite, have exceptionally high melting points, that again can be attributed to the strong #C-C# bonds that make up the solid in 2 or 3 dimensions. Both metals, and network covalent substances exhibit little molecularity.

Low melting points and boiling points are typical of molecular species (high molecularity!). Nitrogen, oxygen, fluorine, and the Noble Gases, are all gases at room temperature, and are comprised of discrete molecular species (diatomic or discrete atomic gases).