The main credit for classifying elements goes to Mendeleev for his
most important contribution to the early development of a Periodic table
of elements wherein he arranged the elements on the basis of their
fundamental property, the atomic mass and also on the similarity of
chemical properties. The formulae of their hydrides and oxides were
treated as basic criteria for the classification of the elements.
However, Mendeleev's classification also had some limitations as it
could not assign the position to isotopes. He also left some gaps in the
periodic table.
36aState Mendeleev's Periodic Law.
307 Why did Mendeleev leave some gaps in the Periodic table ?
1
2) If the letter 'R' was used to represent any of the elements in the
group, then the hydride and oxide of carbon would respectively be
represented as
(i) RHA, RO
(i) RH, ROZ
(ii) RH, RO2
(iv) RH₂, RO
2
Answers
Answer:
a. properties of elements are periodic function of their atomic mass.
b.mendeleev leave some gaps for undiscovered elements.
c.RH4,RO2
d i atoms of elements with similar chemical properties but different atomic masses.
Answer:
Earlier attempts of classification of Elements
Johann Dobereiner Triad model
The first attempt on classification of elements have no definite proof as early man started to classify elements based on his needs. But a scientific method of classification was first introduced by the German chemist Johann Dobereiner in 1829. He classified the elements to groups of three. It should be noticed that there was only less number of elements at that time and many were not discovered. A classification method at that time therefore really deserve appreciation. Dobereiner thus created a law based on his classification and was called Law of Triads.
The name triads came as his classification included elements in a group of three. He also noticed that there was relation in the classified group. The middle element, ie, the second element was having somewhat an atomic mass which was equal to the average mass of other two elements in the group. This was the basis of Law of Triads.
After the long list of classifications the works of this two scientists caused an impact on scientific world. Both came up with same work but Mendeleev was the one with dominance. These 2 personalities are given great respect in chemical world for their contributions. They worked independently and was working on the same method of classification. Dmitri Mendeleev, the German chemist was the first to publish. So the credit goes to him. The basis of their classification was increasing order of atomic weights itself. The difference was the consideration of other physical properties like melting point etc. Mendeleev published the his Law in 1869 and was followed for long time.
Mendeleev's periodic law
The properties of elements are periodic functions of their atomic weights.
But this model also had its own limitations. Still all respect the hard work behind the classification method. Later this classification model which had 8 groups was replaced by modern table with 18 groups prepared by Moseley.