Groups are the vertical column of elements in the Periodic table. They are numbered from 0-7 or 1-8. Elements in the same group have the same number of electrons in the outermost shell i.e. they have the same number of valence electrons. Apart from the eight groups of elements, there are also transition groups of elements which lie between group 2 and 3. Their properties differ from the main group elements.
Periods are horizontal rows of elements, numbered from 1-7. Elements in the same period have the same number of electron shells, i.e. elements in period 1 will have only one shell, which is the K-shell, period 2 has two shells which are K and L shells etc. the number of valence electrons of the elements in the same period increases progressively by one across the period from left to right. Period 6 and 7 are called lanthanide and actinide series respectively. They are also known as inner transition elements.
Note: Group 1 and 2 are called s-block elements because their configuration ends with ‘s’, group 3-8 are called p-block elements because their configuration ends with ‘p’. The transition metals are called d-block elements while the lanthanide and the actinide elements belong to the f-block elements.
