Question

 Using Dobereiner's law of triads find the missing number Li (7),Na (---), K(39) *​

Answer 1

Answer:

according to the Dobereiner middle elements atomic mass is arthmatic mean of 1st and 3rd elements mass thus

massof Na. = (7+39)/2=23

Answer 2

Concept:

According to the Dobereiner's law of triads, The atomic mass of the second element in the triad is approximately equal to the arithmetic mean of the atomic masses of first and third element.

Given:

Atomic mass of first element (Li) = 7

Atomic mass of third element (K) = 39

Find:

Atomic mass of second element (Na)

Solution:

Atomic mass of Na = ( Atomic mass of Li + Atomic mass of K ) / 2

Atomic mass of Na = ( 7 + 39 ) / 2

Atomic mass of Na = 46 / 2

Atomic mass of Na = 23

Hence, the atomic mass of the second element in the triad is 23.

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