Question

What are the main features of Mendeleev's periodic table?

Answer 1

Hint: Mendeleev gave a uniform periodic table in which he arranged elements. The modern periodic table although is based on atomic number, many features are taken from Mendeleev's periodic table. Recall the gaps left by Mendeleev as he predicted an element will take its place that will be discovered later.


Complete step-by-step answer:
The periodic table also called the periodic table of elements is a tabular display of elements based on their atomic number. Before atomic number, atomic mass was considered the basis for arranging elements.
Mendeleev was the first to arrange elements in the tabular form in increasing order of atomic mass. He left a complete column for inert gases which weren’t discovered yet. This is the 18th group of the modern periodic table.
Along with that he left spaces in other groups of his periodic table as he predicted that another element is going to be placed there which will be discovered later.
In this manner, he left a gap below aluminium and germanium. As he did not know the elements, he named them as eka- aluminium and eka- silicon. He even predicted the approximate masses of the two elements.
Later when other elements were discovered, eka- aluminium was the element gallium which is placed below aluminium in the modern periodic table. Similarly, germanium took the place of eka-silicon which is below silicon in the modern periodic table.


Note: The periodic table presented by Mendeleev had some drawbacks as well like,
- Unable to locate hydrogen in the periodic table,
- Increase in atomic mass was not regular while moving from one element to another,
- The isotopes of one element could not be placed or represented in the periodic table.