Quick answer: Mendeleev arranged elements mainly in increasing atomic mass while placing elements with similar chemical properties in the same groups. His table successfully predicted undiscovered elements and corrected some atomic masses. Its limitations included uncertain hydrogen placement, inability to explain isotopes and anomalous element pairs that did not follow atomic-mass order.
What you will learn
- Basis of Mendeleev’s periodic law
- Groups and periods in Mendeleev’s table
- Prediction of undiscovered elements
- Major merits and historical importance
- Limitations resolved by the modern periodic table
Important questions answered
What is Mendeleev’s periodic law?
The properties of elements are periodic functions of their atomic masses.
What was Mendeleev’s greatest achievement?
He left gaps and predicted the existence and properties of undiscovered elements with impressive accuracy.
Why were isotopes a problem for Mendeleev’s table?
Isotopes have different atomic masses but nearly identical chemical properties, so mass-based placement could not explain them.
How did the modern periodic table solve anomalous pairs?
It arranged elements by atomic number rather than atomic mass.
Who should use this lesson?
This lesson is useful for school students, competitive-exam aspirants, parents supporting a learner and teachers looking for a clear explanation. Watch the complete video, make short notes and then practise the ideas without looking at the solution.
Learn with Lalit Kumar Mishra
Lalit Kumar Mishra is a chemistry educator, student success mentor, author and Founder of Topper Formula, with more than 20 years of teaching experience. Explore more learning and mentoring resources on the Resources page.