write short note on mendeleev's periodic law
Answers
Mendeleev's Periodic table .
→ When Mendeleev started his work , 63 elements were known at that time .
→ He examined the relationship between the atomic masses of the elements and their physical and chemical properties .
→ Mendeleev concentrated on the compounds formed by elements with oxygen and hydrogen .
Classification criteria :-
1. The formulae of the hydrides and oxides formed by an element were treated as one of the basic properties of an element foe its classification.
2. He then took 63 cards and on each cards he wrote down the properties of one element. He sorted out the elements with similar properties and pinned the cards todether on the wall .He observed that most of the elements got a place in the periodic table and were arranged in the order of increasing atomic masses .
On this basis , Mendeleev formulated a periodic law .
→ Which states that " The properties of elements are the periodic function of their atomic masses .
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Answer:
Explanation:According to Mendeleev’s Periodic Law, “Physical and chemical properties of elements are periodic function of their atomic masses”.
Mendeleev classified elements according to their atomic masses and arranged these elements in increasing
order of their atomic masses.
Mendeleev classified periodic table into horizontal rows and vertical coloumns. The horizontal rows are called as periods and vertical columns are called groups. Mendeleev’s Periodic Table contains seven horizontal rows and nine vertical columns.
The elements with similar properties comes into same group.
Mendeleev also left gaps in his periodic table for undiscovered elements like aluminum, silicon and Boron in
his periodic table and named them Eka-Aluminium, Eka-silicon and Eka-Boron.
Mendeleev not only predicted the existence of Eka-Aluminium, Eka-silicon and Eka-Boron but also described
the general physical properties of these elements.
These elements discovered later and named as Gallium, Germanium and Scandium.
Mendeleev's periodic table could predict the properties of several elements on the basis of their position in the
periodic table.
Mendeleev's periodic table could accomodate noble gases when they were discovered.
Demerits of Mendleev's periodic table:
The position of isotopes could not explained.
Wrong order of atomic masses of some elements could not be explained.
Position of Hydrogen could not be assigned in a periodic table.