Why couldn’t Mendeleev organize the entire table during his research?

Question

Responses

The elements showed no periodic properties.
The elements showed no periodic properties.

The atomic mass was unknown at the time.
The atomic mass was unknown at the time.

Some elements were undiscovered at the time.
Some elements were undiscovered at the time.

The atomic number was unknown at the time.

Answer 1

Dmitri Mendeleev faced several challenges in organizing his periodic table of elements. The correct reason among your options would be:

Some elements were undiscovered at the time.

Although he was able to group many known elements based on their properties and relative atomic masses, there were certainly elements that had not yet been discovered. This limitation affected his ability to create a complete periodic table.

Additionally, while the atomic number concept (which would later be proposed by Moseley) was unknown during Mendeleev's time, Mendeleev's periodic table was primarily organized based on atomic mass, and he recognized periodic trends based on the chemical properties of the elements. The other options regarding periodic properties and atomic masses do not accurately reflect Mendeleev's challenges in completing his table.