ATOM

Atoms are the basic building blocks of matter. Anything that takes up space and anything with mass is made up of atoms. An atom is a particle of matter that uniquely defines a chemical element.  It consists of a central nucleus that is surrounded by one or more negatively charged electrons. The nucleus is positively charged and contains one or more relatively heavy particles known as protons and neutrons.

Depending on their composition, the different chemical elements are represented and distinguished in the periodic table. Each of the elements has an atomic number and a mass number.