in the periodic table. First period (Atomic number and ): This is the shortest period. It contains only two elements (Hydrogen and Helium). Second period (Atomic number to ): This is a short period.
It contains eight elements (Lithium to Neon). Third period (Atomic number to ): This is also a short period. It contains eight elements (Sodium to Argon). Fourth period (Atomic number to ): This is a long period.
It contains eighteen elements (Potassium to Krypton). This includes representative elements and transition elements. Fifth period (Atomic number to ): This is also a long period. It contains elements (Rubidium to Xenon).
This includes representative elements and transition elements. Sixth period (Atomic number to ): This is the longest period. It contains elements (Caesium to Radon). This includes representative elements, transition elements and inner transition elements (Lanthanides).
Seventh period (Atomic number to ): Like the sixth period, this period also accommodates elements. Recently elements have been included by IUPAC. Figure . Modern Periodic Table *(CAS) Chemical Abstract Service | *(IUPAC) International union of Pure and Applied Chemistry Periodic Classificaiton of Elements .
. Features of Groups The vertical columns in the periodic table starting from top to bottom are called groups. There are groups in the periodic table. Based on the common characteristics of elements in each group, they can be grouped as various families.
Group Number Family Alkali Metals Alkaline earth metals to Transition metals Boron Family Carbon Family Nitrogen Family Oxygen Family (or) Chalcogen family Halogens Noble gases The Lanthanides and Actinides, which form part of Group are called inner transition elements . Except 'group ', all the elements present in each group have the same number of electrons in their valence shell and thus have the same valency. For example, all the elements of group have one electron in their valence shells (1s