Скачать или смотреть Periodic classification of Elements | Class 10 science | chapter 5 | One SHOT | NCERT |One Biology

Periodic classification of Elements Class 10 science chapter 5 One SHOT |NCERT One Biology
Classification of elements in some pattern based on some properties
In 1817, J W Dobereiner, a German
chemist arranged the elements with similar properties into groups and term them as TRIADS.
Triad arranged in order of increasing atomic masses and the atomic
mass of the middle element was roughly the average of the atomic masses
of the other two elements
In 1866 John Newlands an English scientist, arranged the elements in the order of increasing atomic masses.
Every eighth element had properties similar to that of the first elements like musical notes so he called it the ‘Law of Octaves’. It is known as ‘Newlands’
Law of Octaves’.

Mendeleev russian scientist also uses same patern of atomic masses in increasing order for arrangements of elements
.he gave term groups and periods
. There are certain limitaion in above three theoriesso finally came modrern periodic table by H . Moseley

atomic masses increases in groupn and periods

In groups number of valence electrons remain same and number of shells increases
In periods number of valence electrons rincreases by one unit and number of shells iremain same