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प्रश्न
State Dobereiner’s Law of Triads with suitable examples.
उत्तर
Dobereiner’s Law of Triads: “When elements are arranged in order of increasing atomic masses, groups of three elements (known as triads), having similar chemical properties are obtained. The atomic mass of the middle element of the triad being equal to the arithmetic mean of the atomic masses of the other two elements.”
Examples:
Similarity in properties
| Element | Lithium | Sodium | Potassium |
| At. weight | 7.0 | 23.0 | 39.0 |
- All of them are metals. Average wt. of sodium 7 + 39/2 = 46/2 = 23
- All have valency 1.
- They react with water form alkalis and hydrogen gas.
Halogen Group:
| \[\ce{Cl}\] | \[\ce{Br}\] | \[\ce{I}\] |
| 35.5 | 80 | 127 |
- All of them are non-metals
- All have valency one (1).
- Each reacts with water to form acid.
APPEARS IN
संबंधित प्रश्न
The arrangement of elements in a group of three is known as ________.
Name the scientist who gave Law of triads in the early classification of elements.
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?
State one example of a Dobereiner's triad, showing in it that the atomic mass of middle element is half-way between those of the other two.
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
Why was Dobereiner's triad discarded?
What was Dobereiner’s basis, of classification of elements?
Write the characteristic of Dobereiner’s triads?
State Dobereiner’s Law of Triads.
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 |
