No, a single particle can not be an atom. Atoms are composed of subatomic particles. These particles are: 

Protons

Neutrons

Electrons 

If we consider the hydrogen atom which is the simplest atom has one electron and proton. 

What is the matter? 

Everything which we can touch and see is an example of matter. The smallest constituent of the mater is the atom. 

 

Types of mater:

There are two main types of matter: 

Pure substance

Mixture