Atoms

• 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 nucleaus 
• Size-wize it is tiny compared to the rest of the atom 

• Move around the nucleus 
• Negativly charged 
• Tiny, but cover a lot of space 
• The volume of their orbits determines how big the atom is 
• Virtually no mass 
• Arranged in shells around the nucleus.
• The shells explain the whole of Chemistry 

Protons are heavy and positively charged 

Neutrons are heavy and neutral

Electrons are tiny and negatively charged 

              Relative mass       Charge 

Proton           1                    +1

Neutron          1                    0

Electron       0.0005              -1  

• Neutral atoms have no charge overall 
• The charge on the electrons is the same size as the charge on the protons - but opposite 
• This means the number of protons always equals the number of electrons in a neutral atom
• If some electrons are added or removed, the atom becomes charged and is then an ion. 
• The number of neutrtons is not a fixed but is usally about the same as the number of protons.

It is the number of protons in an aom that decides what element it is.

For example... Any atom of the element helium will have 2 protons - and any atom 2 protons will be a helium atom 

Atoms of the same element all have the same number of protons 

-and atoms of diffferent elements will have different numbers of protons 

Elements all have different properties from each other due to differences in their atomic structure