CBSE Class 10 Answered

• In Mendeleev’s periodic table, the noble elements were not included in the table as they were not discovered at that time.

In Modern periodic table, the noble elements were placed in group 18 as a last and separated group.

• In Mendeleev’s periodic table, elements with larger atomic weights were placed before elements with smaller atomic weight without any justified reason.

In modern periodic table, all were arranged systematically with increasing atomic number and weight too.

• In Mendeleev’s periodic table, some different elements were grouped together while some similar elements were placed in different groups. Ex: alkali metals like Li , Na, K were placed with coinage metals Cu, Ag, Au etc.

In Modern periodic table there was no such confusion, the coinage metals have their own position in d-block and alkali metals are placed in s-block elements.

• In Mendeleev’s periodic table, the isotopes were placed in different positions.

In Modern periodic table, the isotopes were assigned same position as they have same atomic number.

• In Mendeleev’s periodic table, elements namely Fe, Co, Ni were placed together in Group VIII.

In Modern periodic table, these elements were placed under d-block elements in different groups.