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.
Lithium, sodium, and potassium are said to be triads in Mendeleev’s periodic table.
Lithium is the first element in the triad and sodium is the second element in the triad (At. mass of Na= 23) and the third element is potassium.
Atomic mass of sodium = At. mass of Li + At. mass of K / 2
= 7 + 39/2
= 23
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