The Periodic Table:
– Shows elements arranged in increasing atomic numbers/ proton numbers
– Has vertical columns called groups and horizontal rows called periods
The group number of an element shows how many electrons there are in that particular element’s outermost shell (valence electrons).
Eg. Sodium (Na) is in Group I and has 1 valence electron while chlorine (Cl), in Group VII, has 7 valence electrons.
The period in which an element belongs to tells us how many electron shells it has.
Eg. Beryllium (Be) is in the second period and has 2 electron shells while selenium (Se) in the fourth period has 4 electron shells.