What is Mendeleev's periodic table ? give important features and draw back of Mendeleev's table.

Mendeleev’s Periodic Law:

Mendeleev, a Russian Chemist used broader range to physical and chemical properties to classify the elements. The physical and chemical properties of elements are periodic functions of their atomic weights. If the elements are arranged in the order of their increasing 

atomic weights, after a regular interval elements with similar properties are repeated (inert gases were not discovered till then)

Mendeleev’s Periodic Table:

Mendeleev arranged the discovered 63 elements in the periodic table into 7 horizontal rows known as periods and 8 vertical columns known as groups numbered 1 to 8. 

Mendeleev Suggested:

(1) He excluded certain elements and assigned them a separate independent position.

(2) Leaving gaps for the then undiscovered elements 

(3) When the properties of elements did not correspond to what is expected of the group they were named by prefixing Eka to the preceding element e.g. Eka boron (Silicon); Eka silicon (Germanium), Eka aluminum (Gallium); Eka Maganese (Technitium) 

Uses of Mendeleev’s Periodic Table:

(1) Systematic study of the elements 

(2) Atomic weights of elements were determined with the help of periodic table. Atomic weight = Valency × Equivalent weight = Group number × Equivalent weight. 

(3) Atomic weight of elements was corrected. Atomic weight of Be was calculated to be 3 × 4.5 = 13.5 by considering its valency 3. Mendeleev calculated it 2 × 4.5 = 9.

(4) Discovery of new elements – In Mendeleev's periodic table two consecutive members differs by two or three units in the atomic weight. Where this gap was more, the gaps were left in the periodic table.

Defects of Mendeleev's Periodic Table:

(1) Position of hydrogen is uncertain. It has been placed in IA and VIIA groups because of its resemblance with both the groups.

(2) No separate positions are given to isotopes.

(3) It is not clear to which group lanthanides and actinides belong to.

(4) Although there is no resemblance except valency of subgroups A and B, they have been put in the same group.

(5) Order of increasing atomic weights is not strictly followed in the arrangement of elements in the periodic table. For e.g. – Co (At.wt. 58.9) is placed before Ni (58.7) and Ar (39.9) is placed before K (39)

Related Questions:

(1) What are the Amphoteric metals ? gives Examples.

(2) Name of total metalloids present in periodic table ?

(3) Total numbers of elements which are liquid at normal temperature is ?

(4) What are the increasing order of molar conductivity of first group elements in water ?

(5) What is atomic density ? give the periodicity of atomic density in periods and groups.

(6) What is atomic volume ? and what is periodicity of atomic volume in groups and periods ?

(7) Why there are 2, 8 and 8 elements in first, second and third periodic of periods table respectively ? Explain.

(8) In alkali metal group which is the strongest reducing agent in aqueous solution and why?

(9) The electron affinity of sulphur is greater than oxygen. Why?

(10) The first ionization energy of carbon atom is greater than that of boron atom, whereas reverse is true for the second ionization energy. Explain.

(11) The electronegativities of B, Al, Ga are 2.0, 1.5, 1.6 respectively. The trend is not regular. Explain.

(12) Li2CO3 decomposes on heating but other alkali metal carbonates don’t. Explain.

(13) Of all noble metals, gold has got a relatively high electron affinity. Explain.

(14 Ionization energy of Boron is smaller than Beryllium even though effective nuclear charge is higher?

(15) What are the increasing order of ioni radii of first group elements in water ?