Atomic Structure

Atomic number = number of protons = number of electrons (an atom is neutral overall)

Mass number = number of protons + neutrons

So for Boron p=5, e=5, n=11-5 =6

Calcium has the electron arrangement 2,8,8,2 so is in group 2, period 4

Isotope = same element but different number of neutrons in it

e.g. hydrogen has no neutrons, deuterium has 1 neutron and tritium has 2 neutrons, but all have 1 proton and 1 electron and are all the element hydrogen