Question

What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev's Periodic Law.

Answer 1

Physical and Chemical properties of the used elements:

1. Mendeleev discovered that element characteristics are connected to atomic mass in a predictable way.
2. He organised the elements in the periodic table so that those with similar properties were placed in the same vertical columns.
3. The atomic mass of an element was the physical property used by him.
4. He used the chemical property of similarity in chemical properties to describe the nature of oxide and hydride produced

Two observations posing challenge:

1. Placing elements in growing order of their atomic masses could not be maintained; the atomic mass of an element has no bearing on its chemical characteristics.
2. Isotopes, on the other hand, were not included in the table because they have unique atomic masses but similar chemical properties.

Hence, for the elements that were yet to be identified, Mendeleev's periodic table did have some gaps. As a result, if a new element is found, it can be assigned to a new group without causing any disruption to the existing ones.