About Periodic Table

Periodic Table is a chart in which various elements are arranged such that similar elements are grouped together. Periodic properties are the properties of elements that are related to the electronic configuration of elements and they change periodically.

Periodicity is the repetition of similar properties of elements after certain typical fixed intervals of atomic numbers when the element is arranged in order of their increasing atomic number.

In 1817, Johann Woldgang Dobereiner arranged the elements with similar properties in groups of three called triads. Example : Li (Lithium), Na (Sodium), K (Potassium) and Cl (Chlorine), Br (Bromine),I (Iodine).

In 1866, John Newlands arranged the elements in the order of increasing number of atomic masses in such a way that every eighth element has the properties similar to the first element similar the octaves found in musical notes.

Example :

Li Be B C N O F
Na Mg Al Si P S Cl

In 1869, Dmitri Lvanvich Mendeleev arranged the elements according to his periodic law which states that “The properties of elements are periodic function of their atomic masses”.

In 1913, Henry Mosely showed that atomic number of an element is a more fundamental property that its atomic mass.

The modern periodic law states that The properties of elements are periodic function of their atomic numbers”. The modern periodic table consists of 18 vertical columns called groups and 7 horizontal rows called periods.


  • Valency increases from 1 to 4 and then decreases to 0
  • Atomic radius decreases from left to right
  • Chemical reactivity decreases first and then increases.
  • Metallic character decreases.
  • Non-metallic character increases.
  • Ionization energy increases.
  • Electron affinity increases


  • All elements have the same valency in a group
  • Atomic radius increases from top to bottom
  • Metallic character gets enhanced.
  • Chemical properties are similar in a group.
  • Ionization energy decreases
  • Electron affinity decreases from the top to bottom.
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