default_background
✕

Find the best tutors and institutes for Class 11 Tuition

Find Best Class 11 Tuition

Please select a Category.

Please select a Locality.

No matching category found.

No matching Locality found.

Q3.3:
What is the basic difference in approach between the Mendeleev’s Periodic Law and the Modern Periodic Law?

Solution :

Step 1: Foundational Theoretical Frameworks

The distinction between Mendeleev’s Periodic Law and the Modern Periodic Law hinges on the fundamental criterion used to organize the chemical elements. This transition represents the shift from empirical observations based on mass to physical observations based on atomic structure.

Feature Mendeleev’s Periodic Law Modern Periodic Law
Primary Variable Atomic Mass Atomic Number ($Z$)
Fundamental Basis Chemical and Physical properties are periodic functions of atomic masses. Chemical and Physical properties are periodic functions of atomic numbers.
Theoretical Origin Observation of repeating patterns in atomic weight and valency. Moseley's X-ray spectroscopic experiments ($1913$).

Step 2: Analytical Comparison of Approaches

A. Mendeleev’s Approach (Atomic Mass):

  • Mendeleev arranged elements in increasing order of their atomic weights [Mendeleev's Periodic Law, 1869].
  • This approach faced significant limitations, specifically the existence of isotopes (elements with the same atomic number but different mass numbers) and the "anomalous pairs" (e.g., Argon ($39.9$ u) preceding Potassium ($39.1$ u) to fit chemical grouping requirements).
  • The reliance on atomic mass resulted in internal inconsistencies regarding the fundamental nature of periodicity.

B. Modern Periodic Law Approach (Atomic Number):

  • Henry Moseley demonstrated that the frequency of X-rays emitted by an element is proportional to the square of its atomic number ($Z$), rather than its atomic mass [Moseley's Law: $\sqrt{\nu} = a(Z - b)$].
  • Atomic number represents the number of protons in the nucleus, which defines the electronic configuration of an atom. Since chemical properties are determined by the arrangement of valence electrons, the atomic number provides a more robust causal mechanism for periodicity [The Pauli Exclusion Principle and Aufbau Principle].

Step 3: Visualizing the Shift in Periodicity

Atomic Variable (Mass vs. Number) Properties Mendeleev (Mass) Modern (Z)

Step 4: Conclusion of the Paradigm Shift

The transition from Mendeleev to the Modern Periodic Law reflects a fundamental shift from macroscopic properties (mass, which is variable due to isotopes) to microscopic electronic reality (the atomic number, which is constant and governs the filling of subshells $s, p, d, f$). This change resolved the issues of isotope placement and the periodic anomalies inherent in the mass-based system.

Final Solution: The basic difference is that Mendeleev’s Periodic Law classifies elements based on increasing atomic mass, whereas the Modern Periodic Law classifies elements based on increasing atomic number ($Z$). The latter is considered superior because it links periodicity to the electronic configuration of atoms, which inherently determines chemical behavior, thereby resolving discrepancies caused by isotopes and anomalous atomic weight pairings.


More Questions from Class 11 Chemistry Classification of Elements and Periodicity in Properties EXERCISES


CBSE Solutions for Class 11 Chemistry Classification of Elements and Periodicity in Properties


Chapters in CBSE - Class 11 Chemistry


Top Tutors who teach Classification of Elements and Periodicity in Properties

Manjunath  Class 11 Tuition trainer in Bangalore
(101)
superTutorSuper Tutor
locationImg Jayanagar East, Bangalore
experience 4 yrs of Exp students 47 students
greenClock 5902 hrs of classes completed
rsIcon 250 per hour
PhD Organic Chemistry at IIT Madras - One to One Tuition and Group Tuition
Online Classes Online Classes
regularClasses Tutor's home

I take classes for grade 11 of Karnataka State PUC, CBSE, ISC, NIOS and Cambridge or IGCSE AS Levels. I have 4 years of teaching experience.

Reena Roy

Attending this introductory chemistry demonstration session offered an insightful look into the program's academic standard. The instructor demonstrated excellent command of the subject matter, skillfully translating intricate chemical principles into accessible intellectual concepts.

Skills: Chemistry
Also teaches: CET Coaching, Class 10 Tuition and more

(19)
Top Tutor
locationImg Jayanagar 4th block, Bangalore
experience 11 yrs of Exp students 1 student
greenClock 296 hrs of classes completed
rsIcon 400 per hour
Home Science and Psychology teacher with 11 years of total teaching experience.
Online Classes Online Classes

- Helping the student gain confidence in themselves and with respect to the subject. - Thorough preparation with the help of model and previous year question papers. - Understanding the student's learning style and adapting my teaching style accordingly. - Making lessons interesting by using different methods of teaching (Sharing relevant YouTube links and weblinks).

Divya

I like the faculty and I feel I had the best environment for my studies . I learned the new things from my teachers who were very helpful in every way they could. You have been a great lecturer to me, and I fully enjoyed your lectures, you explained everything in detail about the media and early childhood education and way of storytelling etc, referring the notes given to us , it made it easier for me to understand. I'm beyond thankful to have you as one of my lecturer in my Masters. Thank you

Skills: Psychology , Home Science

Deepak Joshi Class 11 Tuition trainer in Bangalore
(50)
Top Tutor
locationImg Ashok Nagar D' Souza Layout, Bangalore
experience 13 yrs of Exp students 4 students
greenClock 1062 hrs of classes completed
rsIcon 700 per hour
Ph.D. Candidate | M.Sc. (Mathematics) | Former Faculty at BYJU'S (7 Years) & DPS Gurgaon (6 Years)
Online Classes Online Classes

13+ years of experience teaching Mathematics for grades 10 to 12. • Consistent record of 100% academic results. • Very friendly and supportive learning environment. • Encourages students to ask questions freely and confidently. • Strong focus on conceptual clarity and problem-solving skills. • Helps students build confidence and excel in Mathematics. • Fee structure for one-to-one classes: ₹800 per hour.

Aryan

He is a very good and experienced teacher who helps he improve at maths significantly. I used to get really bad marks earlier and then I started doing classes with him and I saw a significant improvement in my marks. He is one of the best maths teachers I have ever had.

Skills: Mathematics
Also teaches: Class 9 Tuition, Class 10 Tuition and more

(3)
Top Tutor
locationImg Sector 38, Chandigarh
experience 8 yrs of Exp students 1 student
greenClock 10 hrs of classes completed
Online Classes Online Classes

i am a teacher....I am giving home/online tuition since last 8years..I have a degree in masters of biotechnology...My key skills are best in competition as well as theoratical classes...I worked as biology project head in various institute as well as in various schools for preparing kids for NEET and for other medical entrance exams.

Skills: Biology

(1)
Top Tutor
locationImg Suddagunte Palya Balaji Nagar, Bangalore
experience Less than a yr Exp students 2 students
greenClock 27 hrs of classes completed
rsIcon 1000 per hour
Ph.D. Scholar, Researching on AI (Computer Science) and Exoplanetary Science (Physics).
Online Classes Online Classes

I am a Ph.D. Scholar. I completed my BCA from Calicut University, finished my MCA from Kristu Jayanti College (Autonomous), and currently pursuing my Ph.D. in Christ (Deemed to be University). Now, I am doing my research in Artificial Intelligence (Computer Science) and Exoplanetary Science (Physics). Therefore, I have relevant knowledge and experience in Computer Science and Physics concepts, including advanced topics like AI, ML, DL, NLP, Quantum Mechanics, Astrophysics, etc...

Skills: Physics , Computer Science
Also teaches: Class 12 Tuition, Class 10 Tuition and more

Other Subjects in CBSE - Class 11

Worksheet Icon

Download free CBSE - Class 11 Chemistry Classification of Elements and Periodicity in Properties EXERCISES worksheets

Download Now

Find Best Class 11 Tuition ?

Find Now »