Atoms

All substances are amde up of atoms. There are quite a few different models of the atom - but chemists tend to like this nuclear model best. 

The nucleus:

• It's in the middle of the atom.
• It contains protons and neutrons.
• It has a positive charge becuase of the protons.
• Almost the whole mass of the atom is concentrated in the nucleus.
• But size-wise it's tiny compared to the rest of the atom. 

The electrons:

• They move around the nucleus in energy levels called shells.
• They're negatively charged.
• They're tiny, but they cover a lot of space.
• The size of their orbits determines how big the atom is.
• They have virtually no mass.

Protons are heavy and postively charged. Relative mass 1, Relative charge +1.

Neutrons are heavy and…