Atoms

An atom contains a nucleus in the centre


This nucleus consists of protons and neutrons


Electrons surround the nucleus in specific shells (aka. energy levels)


Protons, neutrons and electrons are all known as sub-atomic particles


Each subatomic particle has a different charge and mass


Particle      Charge       Mass     
Proton           +1              1
Neutron          0               1
Electron         -1       Negligible


To remember that the proton is positive - Positive Proton
To remember that the neutron is neutral - Neutral Neutron


A way to remember the two sub-atomic particles that have a mass is by remembering that the mass of an atom is contained within the nucleus, so this must be the proton and the neutron


The atomic number of an element shows the number of protons in the nucleus
In an element, this is equal to the number of electrons surrounding the nucleus of the atom
Because the two particles with a charge are equal, the atom is neutral as the positive protons and the negative electrons cancel out each others charge


The mass number of an element shows the number of protons and neutrons in the nucleus


To calculate the number of neutrons in an atom, subtract the mass number from the atomic number