Question

How many periods & groups were present in Mendeleev's periodic table?

Answer 1

Hint: In chemistry, all elements are arranged in a specific order, according to their physical and chemical properties. This arrangement is known as the periodic table arranged by many scientists according to their research and study.

Complete step by step answer:
Periodic table - It consists of periods and groups. Periods shows a horizontal line while the group is vertical.
 As we know that many scientists try to arrange elements in order. But, some failed and succeeded.
The first arrangement was given by Johann Wolfgang Dobereiner in $1829$. He used the triad to represent them. He had kept along those elements that have a similar property. He gave four successful triads.
The second arrangement was given by John Alexander Newland in \[1866\]. He arranged elements according to increasing mass. He arranged a total of $56$ elements in which the first was hydrogen and the last was thorium.
The next scientist Dmitri Ivanovich Mendeleev arranged elements according to their atomic mass, fundamental property, and chemical property. He arranged a total $63$ element. In this arrangement, there are seven horizontal rows and eight vertical groups.
In this arrangement the first element was hydrogen and the last was uranium.
After these attempts, Henry Moseley arranged elements according to atomic numbers in $1913$. This table is known as the modern periodic table in which total $18$ groups and $7$ elements.

Note:
There were a few limitations of the Mendeleev periodic table like the position of hydrogen was not fixed, the position of isotopes, Anomalous position of pairs of the element, no similarity within sub-groups, no new element would discover, similar element in a different group.