Chapter 3
Chapter 3
PERIODIC TABLE AND PERIODICITY OF PROPERTIES
Q.1 What are the contributions of Dobereiner, Newland, Luthar Meyer and Mendeleef in the present shape of long form periodic table ?
Dobereiner’s Triads : In 1829, a German scientist, John Dobereiner classified specific elements into groups in order of increasing atomic masses. Each group has three elements. He named these groups as triads.He noticed that the atomic mass of the middle elements was found to be approximately equal to the arithmetic mean of the other two elements. The Dobereiner’s method of classification was failed in arranging all elements. The elements were selected out of those known at that time. Therefore the idea of triads was rejected.
Newland’s Law of Octaves : In 1864, John Newland, an English chemist arranged the elements in the order of their increasing atomic masses. He noticed that the properties of the elements were repeated at every eighth element. Newland called this as the law of octaves. Newland’s classification of a few elements is shown in the following table.
Note:The numbers in parentheses are atomic masses.
Table: Newland’s law of octaves.
I II III IV V VI VII
H
(1) Li
(7) Be
(9) B
(121) C
(12) N
(14) O
(16
F
(19) Na
(23) Mg
(24) Al
(27) Si
(28) P
(31) S
(32)
Cl
(35.5) K
(39) Ca
(40)
From the above table , we can see that the properties of sodium (11Na) and potassium (19K) are similar to those of lithium (3Li). In the same way, chlorine (17Cl) resembles fluorine (9F).
Newland’s classification failed badly while dealing with the heavier elements beyond calcium .
Luthar Meyer’s Atomic Volum Curves : In 1869, a German chemist, Julius Luthar Meyer drew a graph of atomic volume versus atomic mass for a variety of elements. He found that the elements with similar properties occupied alike positions on the curve as shown in following Fig.
For instance, alkali metals (Li, Na, K, Rb, Cs, etc.) occupy the peak positions.
PERIODIC TABLE AND PERIODICITY OF PROPERTIES
Q.1 What are the contributions of Dobereiner, Newland, Luthar Meyer and Mendeleef in the present shape of long form periodic table ?
Dobereiner’s Triads : In 1829, a German scientist, John Dobereiner classified specific elements into groups in order of increasing atomic masses. Each group has three elements. He named these groups as triads.He noticed that the atomic mass of the middle elements was found to be approximately equal to the arithmetic mean of the other two elements. The Dobereiner’s method of classification was failed in arranging all elements. The elements were selected out of those known at that time. Therefore the idea of triads was rejected.
Newland’s Law of Octaves : In 1864, John Newland, an English chemist arranged the elements in the order of their increasing atomic masses. He noticed that the properties of the elements were repeated at every eighth element. Newland called this as the law of octaves. Newland’s classification of a few elements is shown in the following table.
Note:The numbers in parentheses are atomic masses.
Table: Newland’s law of octaves.
I II III IV V VI VII
H
(1) Li
(7) Be
(9) B
(121) C
(12) N
(14) O
(16
F
(19) Na
(23) Mg
(24) Al
(27) Si
(28) P
(31) S
(32)
Cl
(35.5) K
(39) Ca
(40)
From the above table , we can see that the properties of sodium (11Na) and potassium (19K) are similar to those of lithium (3Li). In the same way, chlorine (17Cl) resembles fluorine (9F).
Newland’s classification failed badly while dealing with the heavier elements beyond calcium .
Luthar Meyer’s Atomic Volum Curves : In 1869, a German chemist, Julius Luthar Meyer drew a graph of atomic volume versus atomic mass for a variety of elements. He found that the elements with similar properties occupied alike positions on the curve as shown in following Fig.
For instance, alkali metals (Li, Na, K, Rb, Cs, etc.) occupy the peak positions.