# What is the basic unit of matter.?

$\text{The atom..........}$
There are about 100 or so different types of atoms, i.e. elements, which are all conveniently listed on the Periodic Table. Each individual atom contains massive particles with positive charge, and negatively charged particles with ZERO rest mass, that are conceived to whizz about the positively charged nuclear core. The number of positively charged particles in the nucleus gives $Z$, $\text{the atomic number}$, and this number defines the identity of the element. $Z = 1$, the element is hydrogen; ......$Z = 6$, the element is nitrogen; .........$Z = 79$, the element is gold.