The primary difference between the modern periodic table and Mendeleev's periodic table is:
The primary difference between the modern periodic table and Mendeleev's periodic table is the arrangement of elements.
Mendeleev's periodic table was organized based on the atomic masses of elements and laid out in a way that elements with similar chemical properties were grouped together. He left gaps in the table for undiscovered elements, predicting their properties based on the trends he observed.
On the other hand, the modern periodic table is organized based on the atomic numbers of elements, which represent the number of protons in an atom's nucleus. In the modern table, the elements are arranged in order of increasing atomic number, and elements with similar properties are placed in the same groups.
Additionally, the modern periodic table includes elements that were not known or discovered during Mendeleev's time, as well as synthetic elements that have been synthesized in laboratories. It also provides more detailed information about each element, including its atomic mass, atomic number, electron configuration, and additional properties.