Page 1 - 2. HA-WS -13 Ch-5 CLASSIFICATION BY DOB.& NEWL.

SAI International School
Class-X

Subject_ Chemistry
Topic- Periodic Classification
Sub topic- Dobereiner’s Classification & Newland's Law of Octave

Lesson Notes

➢ Introduction-
- It is always easy to distinguish items from one another by sorting them on
some basis.

- In malls or in shops we always get the things sorted at their respective
places.

- Kids wear can be bought from kid section which cannot be found in any
other section.

- Grocery shops also align the items in a systematic way.

- Similarly, the 118 elements, that we have, need to be sorted and organized,
in order to study them easily and understand their properties

- There are around 92 well known naturally occurring elements of which 70
are metals and remaining 20 are the non-metal

- Some elements possess characteristics of both metals as well as non-
metals. They are termed as metalloids.
For example- boron, silicon, germanium, arsenic, antimony, tellurium, and
polonium.

 About 200 years back, scientists felt the need for classification and started
classifying the, then existing elements.

Döbereiner was one of the first scientists, who tried to classify the, then existing
33 elements as per their similarities in properties.

• Dobereiner's Classification-
- In 1817 a German chemist Johann Wolfgang Döbereiner arranged the
elements with similar properties into groups.

- Some groups were identified having three elements each. So, he called
these groups ‘Triads’.

- A Triad is a grouping of three elements in the increasing order of their
atomic mass.

The average of the first and third elements' atomic masses is the atomic mass
of the second element.

- Only three triads could be identified from the 33 elements discovered then.

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