Question

write the achievements of Mendeleev's Periodic table and limitations of Newland's law of octaves? 5 marks​

Answer 1

Answer:

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Explanation:

•) The achievements by Mendeleev were:

•Mendeleev kept some blank spaces in the periodic table for the elements that were yet to be discovered.

Eg:- Eka-aluminium, Eka-boron, Eka-silicon.

•He also predicted properties of some elements which were yet to be discovered.

Eg:- The properties of Eka-aluminium predicted by Mendeleev and those of element gallium were almost the same.

•When noble gases were discovered, they could be placed in a new group without disturbing the order.

The formula of the hydrides and oxides formed by an element were treated as one of the basic the properties of an element for its classification.

•) Limitations of law of octaves: The law of octaves has the following limitations ;

(A) The law of octaves was found to be applicable only upto calcium. It was not applicable to elements of higher atomic masses.

(B) Position of hydrogen along with fluorine and chlorine was not justified on the basis of chemical properties.

(C) Newlands placed two elements in the same slot to fit elements in the table. He also placed some unlike elements under the same slot. For example, cobalt and nickel are placed in the same slot and in the column of fluorine, chlorine and bromine. But cobalt and nickel have properties quite different from fluorine, chlorine and bromine. Similarly, iron which has resemblances with cobalt and nickel in its properties has been placed for away from these elements.

Thus, it was realized that Newlands’ law of octaves worked well only with lighter elements. Therefore, this classification was rejected.

Answer 2

Answer:

1. MENDELEEV ARRANGED THE ELEMENTS IN INCREASING ATOMIC MASSES.
2. HE LEFT SPACES FOR THE ELEMENTS THAT WERE STILL LEFT TO BE FOUND LIKE GALLIUM, SCANDIUM AND GERMANIUM.
3. ACCOMODATE NOBLE GASES WHEN THEY WERE DISCOVERED WITHOUT DISTURBING THE ORIGINAL ARRANGEMENT.

LIMITATION OF NEWLAND'S LAW OF OCTAVES-

• IT WAS APPLICABLE UPTO CALCIUM(FOR LIGHTER ELEMENTS ONLY)
• PROPERTIES OF NEW DISCOVERED ELEMENTS DIDNOT FIT INTO HIS LAW OF OCTAVE.
• to fit elements into a stable newlands sportive even two element together in one slot and that too in the column of unlike elements having very different properties