Question

In what order did Mendeleev arrange the elements in the periodic table?

Answer 1

Mendeleev proposed a classification in 1869 that listed the elements in order of increasing atomic mass, and clustered elements with similar qualities into families one above the other.

Complete answer:
Mendeleev organised the 63 elements that were known at the time in ascending order of atomic masses. He left a gap in the periodic table if a certain element did not fit into the arrangement. As a result, Mendeleev left several gaps in the periodic table for unknown elements. This aids in the large-scale discovery of elements to a significant extent.
Instead of increasing atomic mass, the current classification of elements ranks them by increasing atomic number.

Additional Information:
Limitations of Mendeleev’s periodic table:-
Position of hydrogen: Hydrogen has an electronic configuration similar to that of an alkali metal. It does, however, exist as diatomic molecules, just like halogen. As a result, hydrogen has no set location.
Position of isotopes: Isotopes were found several years after Mendeleev suggested periodic categorization of elements.
Anomalous position of some elements: Although the elements are grouped in order of increasing atomic mass, the element with the higher atomic mass may precede the element with the lower atomic mass in some situations.

Note:
It's also worth noting that Mendeleev's 1871 arrangement was based on atomic ratios in which elements produced oxides, binary compounds with oxygen, but today's periodic tables are organised by rising atomic numbers, or the number of protons in a certain element.