The Modern Periodic Table is a system of representing chemical elements as a table with their corresponding characteristics. The chemical elements in the periodic table are decorated in ascending order of atomic number and classified into periodic, primary group, secondary group. The current periodic table contains 118 known elements. 


John Wolfgang Dobereiner, a German scientist, first attempted to arrange the element in 1829.
John Wolfgang Dobereiner
Alkali Metal Group: The element Lithium Sodium and potassium have similar chemical properties and from triads.
For examples:
  • All the elements are metal.
  • All of them react with water to form alkali and hydrogen gas.
  • All of them has a valency of 1.
Alkali metal:- Group 1: H, Li, Na, K, Rb, Cs, Fr.

Alkaline earth metal group:  The element calcium Strontium and barium have similar chemical properties and form a triad.
For example:
  • All this element are metal.
  • The oxides of all of them are alkaline in nature.
  • All this element have a valency of 2.
Alkaline earth metal:- group 2: Be, Mg, Ca, Sr, Ba, Ra.
Halogen group:  The element chlorine bromine and Iodine have similar chemical properties and form a triad.
For example:
  • All these elements are non-metal.
  • All the elements react with H2O to form acid.
  • All this element has a valency -1.
Halogen group:  group 17: F, Cl, Br, I, At, Ts.

Oxygen Family: 
  • The three elements Sulphur Selenium and Calcium have similar properties. They constitute yet another Dobereiner's triads.
  • Belong to the oxygen family because the first element of this group is Oxygen.


Newland's Law of Octaves:- Newland's started with the element having the lowest atomic mass such as Hydrogen and ended at Thorium, which was the 56th element.
John Alexander Newland
Newland's arrangement of elements is known as " Law of octaves" as in his arrangement every element had the properties similar to that of the first. Eg; the properties of Lithium and Sodium were found to be the same.

Newland's:- First element = Hydrogen(H).
                      Last element = Thorium(Th).
                      Total element = 56.
John Alexander Newland's, an English scientist also attempted to arrange the known elements in 1866.
John Newland's had followed the order of increasing atomic masses to arrange the elements.

The Royal Society, London recognized the work of Newland's much later and awarded with the " Davy Medal" in 1887.


Introduction: Dmitri Ivanovich Mendeleev, a Russian chemist, who successfully attempted to arrange the elements.
Dmitri Ivanovich Mendeleev
Points To Remember:
  • Mendeleev's arranged the elements based on their fundamental property, the atomic mass, as well as on the similarity of chemical property.
  • During the Mendeleev's time, only 63 elements were known.
  • Mendeleev's Periodic Table consists of 8 vertical columns known as "Group" and 7 horizontal rows known as "Periodic".
  • Mendeleev's Periodic Law states that " The property of elements are the periodic function of the atomic masses".
  • Mendeleev's arranged the sequence in inverted fashion so that elements with similar properties could be grouped together.
  • Mendeleev's left space for some elements, which were not discovered at that time, he boldly predicted about the existence of future elements.

Mendeleev's:- First element = Hydrogen(H).
                          Last element = Uranium(U).
                          Total element = 63.


Introduction: In 1913, Henry Moseley, an English Physicist discovered that the atomic number of elements is a more fundamental property in comparison to its atomic mass.
Henry Moseley
Points To Remember:-
  • Based on Moseley's discovery, Mendeleev's periodic law was modified and the atomic number was adopted as the basis of Modern Periodic Table.
  • The modern periodic law, "The properties of elements are the periodic function of their atomic number".
  • 18 vertical columns known as "Group".
  • 7 horizontal rows known as "Periods".
  • Notes: 1. Mercury is a liquid Metal & 2. Bromine is a liquid Non-Metal.
Important Points:-
  • Group-1 = Alkali Metal.
  • Group-2 = Alkaline Earth Metal.
  • Group-(3-12) = Transition elements.
  • Group-13 = Boron family.
  • Group-14 = Carbon family.
  • Group-15 = Nitrogen family or Pnicogens (Produce suffocation).
  • Group-16 = Oxygen family or Chalcogen.
  • Group-17 = Halogen.
  • Group-18 = Noble gases or Inert gases.
GROUP: 1-2 = S-Block => Total 13 elements.
GROUP: 3-12 = D-Block => Total 40 elements.
GROUP: 13-18 = P-Block => Total 37 elements.
Lanthanides & Actinides = F-Block => Total 28 elements.

Total: Elements = 118
             Metals = 91
             Non-Metals = 20
             Metalloids = 7

Metalloids: Boron (B), 
                      Silicon (Si),
                      Germanium (Ge), Arsenic (As),
                      Antimony (Sb), Tellurium (Te),
                      Polonium (Po).


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