## Can the following groups of elements be classified as Dobereiner’s triad?

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Answer
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Dobereiner triads are those in which elements are arranged in such a way that the
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atomic mass of the middle
**

*element*

*is the mean**of the atomic masses of the first and third element.*

(a) Na, Si, Cl

Atomic mass of Na = 23 amu

Atomic mass of Si = 28 amu

Atomic mass of Cl = 35.5 amu

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The mean of first and third
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elements i.e Na and Cl= (23 + 35.5)/2 =
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29.25
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Since the
atomic mass of Si is
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not equal to the mean
**
of atomic masses of first and third elements
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,
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this is
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not a Dobereiner’s Triad.
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(b) Be, Mg, Ca

Atomic mass of Be=9 amu

Atomic mass of Mg=24 amu

Atomic mass of Ca= 40 amu

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The mean of first and third
**
elements i.e. Be and Ca= (40 + 9)/2 =
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24.5
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Since the atomic mass of Mg is
**
equal to the mean
**
of atomic masses of first and third elements, this
**
is a Dobereiner’s Triad.
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