Q27 of 52 Page 43

The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.

The arrangement of these elements is known as Dobereiner triad. This triad is a group of three elements.


In 1817, Dobereiner suggested relationship between properties of elements and their atomic weights. The atomic weight of the middle element is approximately equal to the average weights of other two elements.


One example of such as set of elements is lithium, sodium and potassium.


Here, atomic weight of sodium is average weights of the lithium and potassium.


7 (lithium) + 39 (potassium)/2 = 23 (sodium)


More from this chapter

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25

On moving from left to right in a period in the periodic table, the size of the atom.

 26

Which of the following set of elements is written in order of their increasing metallic character?

 28

Elements have been arranged in the following sequence on the basis of their increasing atomic masses.

F, Na, Mg, Al, Si, P, S, Cl, Ar, K


(a) Pick two sets of elements which have similar properties.


(b) The given sequence represents which law of classification of elements?

 29

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

(a) Na, Si, Cl


(b) Be, Mg, Ca


Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40


Explain by giving reason.