No, a photon is not an atom. A photon is a fundamental particle of light and other forms of electromagnetic radiation. It is a quantum of the electromagnetic field and carries energy and momentum. Photons have no mass and travel at the speed of light in a vacuum.
On the other hand, an atom is the basic unit of matter and consists of a nucleus made up of protons and neutrons, surrounded by electrons. Atoms are the building blocks of molecules and have mass.
In summary, photons and atoms are fundamentally different entities. Photons are massless particles of light, while atoms are the smallest units of matter that retain the properties of an element.