Question

Which of the following statements is not true about Dobereiner’s law of triads?
A.This law was applicable to all known elements
B.Nitrogen family does not obey the law of triads
C.Dobereiner’s classification was not very useful
D.The atomic mass of the central element of each triad was merely the arithmetic mean of the atomic masses of the other two elements

Answer 1

Hint: We know that before constructing the modern periodic table, there were many attempts to classify elements. Among them, Dobereiner triads, Newlands law of octaves is important.

Complete step by step answer:
First we discuss Dobereiner triads. Law of triads was given by a German scientist whose name is Johann Wolfgang Dobereiner. He observed that the group of three elements could be formed in where all the elements possess similar physical and chemical properties. According to this law of triads, the arithmetic mean of the first and third element of the triad is equal to the atomic mass of the second element. The triads identified by him was, Lithium, sodium, potassium (triad 1), calcium, strontium, barium (triad 2), chlorine, bromine, iodine (triad 3), sulphur, selenium, tellurium (triad 4) and iron, cobalt, nickel (triad 5).

Let's find the incorrect options regarding Dobereiner triads.
-Option A says that this law is applicable to all elements which is not correct as the several known elements at that time do not fit into the triads.
-Option B says that nitrogen family does not follow the law of triads which is correct as only five triads are discovered.
-Option C says that this law is not very successful which is correct as all the newly discovered elements do not fit into the triads.
-Option D says the arithmetic mean of the first and third element of the triad is equal to the atomic mass of the second element which is correct.

So, option A is the correct answer.

Note:
Doberiener’s triads and Newlands law of octaves were the early attempts made to group elements on the basis of their properties. According to Newland’s law of octaves, every eight elements possess similar properties on arranging elements in order of increasing atomic mass.