Question

What was Dobereiner's law??
What was d drawbacks??​

Answer 1

Answer:

It is a law proposed by dobernier to classification of elements.

Explanation:

Traid means a set of three elements. dobernier classified all elements in to traids and said that for each and every traid the atomic weight of middle element is equal to average of Atomic weights of other two elements.

Eg: (S, Se, Te).[16th group elements].

Draw backs : it was failed because it is applicable to only few elements and failed to explain for further discovered elements.

However, it is basic classification of elements in periodic table.

Answer 2

Answer:

Dobereiner's law of triads :

Dobereiner arranged the three elements in a triad in an increasing order of atomic mass and showed that the atomic mass of the middle element was approximately equal to the mean of the atomic masses of the other two elements.

Drawbacks of Dobereiner's law of triads :

1. All the known elements at that time could not be classified into the Dobereiner's triads.

2. It was an approximation and not the correct value.

3. The more fundamental property of the passed elements i. e. atomic number is not seen in Dobereiner's law of triads.

4. It is proved false in case of isotopes as they have same chemical properties but different atomic masses.

Explanation:

1. Elements are classified for the easiness of their studies.

2. Dobereiner was the first to classify the elements based on atomic masses of the elements.

Concepts:

1. Triad :

The group of three elements each, having similar chemical properties is called triad.

2. Atomic mass :

The sum of number of protons and neutrons present in the nucleus of an atom is called atomic mass.

3. Atomic number :

The number of either protons present in the nucleus or the electrons moving in the shells is called atomic number.

Illustration of Dobereiner's law of triads :

1. Lithium, sodium and potassium form Dobereiner's triad.

2. They show similar chemical properties.

3. Their atomic masses are as follows :

Element ⟶ Atomic mass

Li ⟶ 6.9

Na ⟶ 23

K ⟶ 39.1

According to Dobereiner's law of triads, the atomic mass of the middle element is approximately arithmetic mean of the atomic masses of the other two elements.

$\frac{6.9 + 39.1}{2}$

It is approximately the 23.0 atomic mass of sodium.

Thus, the atomic mass of sodium (23) is the average of the atomic masses of lithium (6.9) and potassium (39.1).

Few more examples of Dobereiner's triads :

1. S (32.1), Se (79.0), Te (127.6)

2. Be (9.0), Mg (24.3), Ca (40.1)