Rita and Geeta were studying the chapter on Periodic Classification of Elements. They found an interesting relation between the atomic masses of Li, Na and K. The atomic masses of Li, Na and K are 7, 23 and 39 respectively. They found that the atomic mass of the middle atom Na is the average of the masses of the other two elements. "That is amazing. Let us find out some other groups of three elements having such a relation in their atomic masses", said Rita to Geeta. a. Can you find two other groups of three elements having approximately similar relation between the atomic masses? b. What are such groups of elements called? Who noticed this phenomenon first? c. Do you think such groups were possible in the periodic table?
Answers
Answer:
This is an example of Dobereiner's triads which is a group of three elements. In Dobereiner's triads the atomic masses of elements are arranged in such a way that the atomic mass of middle element is almost the mean of atomic masses of first and third elements.
For example; Ca, Sr and Ba is one of the Dobereiner's triads. Here, atomic masses of Ca, Sr and Ba are 40, 88 and 137 respectively. Atomic mass of Sr that is 88 is almost the mean of atomic masses of Ca and Ba.
Explanation:
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Answer:
the other groups are Ca,Sr,Ba(Alkaline earth metal) and Cl,Be,I (halogens) whose mass relations are given in pics attached.
such groups are called triads
it was first noticed by German chemist, John Dobereiner
such groups are not possible in periodic table because all the elements cannot be put into periodic table in the form of triads having similar chemical properties there was only 3 triads from the elements known.
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