How did mendeleev organize the elements to create a periodic table

By definition, Mendeleev's periodic table was rearranged according to atomic number, hence there are 7 periods (rows) and 18 groups (columns)

Mendeleev proposed to arrange the elements in lines and columns (also called "periods" and "groups") within a rectangle, with their atomic weights in ascending order from left to right within the same line down to the second and so on.

In other words, the elements are ordered by atomic number, which is defined as the number of protons found in the nucleus.

Also, Mendeleev showed that elements with similar chemical properties appeared periodically, giving rise to eight groups.

In this way he reorganized the periodic table leaving holes where an element did not exist, so that it can be discovered.

Finally, in summary, Mendeleev's periodic table was rearranged according to atomic number, hence there are 7 periods (rows) and 18 groups (columns).

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