C2

Atoms consist of 3 main  particles. These are called protons, neutrons and electrons.

Protons: - positively charged

             - relative mass of 1

             - to find how many protons there are, look at the elements atomic number

Neutrons: - charge of zero

               - relative mass of 1

               - to find how many neutrons there are, find the particles' atomic mass, and then                  subtract the elements atomic number

Electrons: - negatively charged

                - a relative mass of basically nothing

                - to find how many electrons there are, look at the elements atomic number

In the middle of an atom, there is a nucleus. This consists of protons and neutrons. This means that the nucleus has an overall positive charge, and the nucleus accounts for most of the overall mass of the atom.

In the periodic table, the elements are put in increasing order of atomic number (how many protons the element has).

Electrons are arranged in shells outside the nucleus. The innermost shells are always filled up before the others.Each shell has a maximum amount of electrons that they can hold. 

1st shell: 2 electrons

2nd shell: 8 electrons

3rd shell: 8 electrons

4th shell: 12 electrons