Cells are the building blocks of life and atoms are the building blocks of cells. Atoms are what make up everything. You may have a billion or so cells but you also have well over a billion atoms that make up that cell.   

In chemistry we spend a lot of time looking at atoms so knowing a bit about what they are made of is always helpful – you couldn’t build a very good car without knowing that it contains an engine. The diagram shows all the main particles that make up an atom and the table below that gives some information about each of the particles:

Let’s look at the charges and at the masses. You have positive protons and negative electrons. In an atom there are equal numbers of each so atoms must be neutral – positive plus negative equals zero. The masses are expressed in atomic mass units (AMU). They have such a small mass that it is better to make a new unit.