The atomic masses of three elements X, Y and Z having similar chemical properties are 7, 23 and 39 respectively.

(a) Calculate the average atomic mass of elements X and Z.

(b) How does the average atomic mass of elements X an Z compare with the atomic mass of element Y ?

(c) Which law of classification of elements is illustrated by this example ?

(d) What could the elements X, Y and Z be ?

(e) Give another example of a set of element which can be classified according to this law.

(a) We have to calculate the average atomic mass of elements X and Z

Avg. atomic mass= Atomic mass of X + Atomic mass of Z

Avg. atomic mass= 7+39/2

Avg. atomic mass= 23

(b) The average atomic mass of elements X and Z is equal to the element Y.

So X, Y and Z elements follow the law of Doberenier’s.

(c) The given elements follow the law of Doberenier.

(d) The atomic mass of X element is 7, so this element is Lithium. The atomic mass of Y element is 23, so this element is Sodium and the atomic mass of Z element is 39 so this element is Potassium.

(e) The three elements chlorine, bromine and iodine also follow the law of doberenier.