the periodic table has a load of elements in it.
all the elements have been found which are on there.
chemists usually use the periodic tables as they need to know what element is in the medicine.
all elements are in certain groups.
what the numbers mean
you minus the a mass by the a number to find the number of neutrons.
the atomic mass tells you the number of just protons and electrons in the element.
you can only have a certain amount of electrons on each shell,
shell one = 2 electrons .
shell two = 8 electrons.
shell three = 8 electrons.
shell four has only 18 electrons.