The elements in the periodic table are arranging according to INCREASING PROTON NUMBERS.
The vertical columns are known as Groups while the horizontal rows are known as Periods.
Elements of the same group have the same number of valence electrons ( outershell electrons)
Eg:
All ements of group 1 have 1 valence electrons;
All elements of group 2 have 2 valence electrons.
Elements of the same period have the same number of electron shells.
Eg:
All elements of period 1 ( Hydrogen and Helium ) have 1 electron shell.
All elements of period 2 (Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Sulphur, Fluorine, Neon ) have 2 electron shells.
There exist a group of elements without any grouping.
These are the transition metals.
Transition metals are characterized by their variable ( more than 1 ) valencies.
Eg:
iron ion exist as iron (II) ion and iron (III) ion;
copper ion exist as copper(I) ion and copper(II) ion.
