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प्रश्न
Can the following groups of elements be classified as Dobereiner's triads?
(a) Na, Si, Cl
(b) Be, Mg, Ca
Give reason for your answer.
(Atomic masses : Be 9 ; Na 23 ; Mg 24 ; Si 28 ; Cl 35.5 ; Ca 40)
उत्तर
(a) The atomic masses of Na, Si and Cl are 23, 28 and 35.5 respectively.
According to Dobereiner's law of triads, when elements are arranged in the increasing order of their atomic masses, a three element group with similar chemical properties is obtained. The atomic mass of the middle element is equal to the arithmetic mean of the atomic masses of the other two.
The above set of elements does not form a triad because arithmetic mean of the atomic masses of Na and Cl `=(23+35.5)/2=29.25`
This value is approximately equal to the atomic mass of silicon, but they do not form a triad because the elements do not exhibit similar chemical properties.
(b) The set of elements Be, Mg and Ca with atomic masses 9, 24 and 40 respectively, form a triad because they have similar chemical properties and the atomic mass of magnesium (Mg) is approximately equal to the average of the atomic masses of beryllium (Be) and calcium (Ca).
The arithmetic mean of the atomic masses of Be and Ca `=(9+40)/2=24.5` which is approximately equal to 24.
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संबंधित प्रश्न
The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation or all the three attempts.
A, B and C are the elements of a Dobereiner's triad. If the atomic mass of A is 7 and the of C is 39, what should be the atomic mass of B?
The three imaginary elements X, Y and Z represent a Dobernener's triad. If the atomic mass of element X is 14 and that of element Y is 46, then the atomic mass of element Z will be:
(a) 28
(b) 60
(c) 78
(d) 72
Did Dobereiners triads also exist in the columns of Newland's Octaves? Compare and find out.
With an example, explain Dobereiner's Triads.
Dobereiner laid down the _______ rule.
In Dobreiner's triads, three elements appear to be arranged in ascending order of their atomic number.
Match the following.
| 1. | Triads | Newlands |
| 2. | Alkali metal | Calcium |
| 3. | Law of octaves | Henry Moseley |
| 4. | Alkaline earth metal | Sodium |
| 5. | Modern Periodic Law | Dobereiner |
Pick out the chemically most reactive elements from the given triads.
Li, Na, K F, Cl, Br
Can the following groups of elements be classified as Döbereiner's triad?
- Na, Si, Cl
- Be, Mg, Ca
Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40 Explain by giving reason.
