Question: Why is light not a element?

Piers Barnes answered on 13 Jan 2017:

Light is not considered to be one of the elements due to the way particles are classified. Light can be considered as a made up of particles – photons. However, photons have a different set of properties to the atoms that form the elements. Photons are a type of (electromagnetic) force carrying particle and we are not aware that they are composed of any other sub-particles, it has no rest mass and is part of the Boson family of particles. This means that there is no restriction on how many can be in the same place in the same state. Atoms are a kind of composite particle consisting of electrons and nucleons (protons and neutrons) which are in turn composed of quarks and gluons, they have a rest mass, and they belong to the Fermion family which means they cannot occupy the same state and position simultaneously.