How did Mendeleev's table differ from earlier attempts like Newlands' Law of Octaves?

Mendeleev's table was a significant improvement because it was more comprehensive and had predictive power. While Newlands' Law of Octaves also used atomic mass and observed periodicity, it only worked for lighter elements and failed for heavier ones. Mendeleev, however, prioritized chemical properties, left deliberate gaps for undiscovered elements, and even corrected atomic masses, making his classification far more robust and universally applicable at the time.

What were the most significant merits of Mendeleev's Periodic Table?

The most significant merits include the systematic classification of elements, which simplified their study; the accurate prediction of the existence and properties of several then-undiscovered elements (like Eka-aluminium and Eka-silicon); and the correction of doubtful atomic masses of certain elements (like Beryllium). These achievements validated his law and demonstrated its profound utility in chemistry.

What are 'anomalous pairs' in Mendeleev's table, and why were they a problem?

Anomalous pairs, also known as inverted pairs, refer to instances where Mendeleev had to place an element with a higher atomic mass before an element with a lower atomic mass to maintain the consistency of chemical properties within a group. Examples include Argon (39.9) before Potassium (39.1) and Tellurium (127.6) before Iodine (126.9). This was a problem because it violated his own fundamental principle of arranging elements strictly by increasing atomic mass.

Why couldn't Mendeleev assign a fixed position to hydrogen and isotopes?

Hydrogen's position was problematic because it exhibits properties similar to both alkali metals (Group 1) and halogens (Group 17), making a single, unambiguous placement difficult. For isotopes, since they have different atomic masses but identical chemical properties, Mendeleev's atomic mass-based law would require them to occupy different positions, which contradicts their chemical identity. This issue arose because isotopes were unknown during his time.

Mendeleev's Periodic Law

Q: What is the fundamental principle of Mendeleev's Periodic Law?

Mendeleev's Periodic Law states that the properties of elements are a periodic function of their atomic masses. This means that when elements are arranged in increasing order of their atomic masses, elements with similar chemical and physical properties reappear at regular intervals. This periodicity allowed Mendeleev to group elements with similar characteristics together, forming the basis of his periodic table.

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Dmitri Mendeleev's Periodic Law, proposed in 1869, states that 'The properties of the elements are a periodic function of their atomic masses.' This fundamental principle guided his arrangement of the known elements into a table, which became the precursor to the modern periodic table. Mendeleev observed that when elements were arranged in increasing order of their atomic masses, elements with sim…

Quick Summary

Mendeleev's Periodic Law, proposed by Dmitri Mendeleev in 1869, states that the properties of elements are a periodic function of their atomic masses. This means that when elements are arranged in increasing order of their atomic masses, elements with similar chemical and physical properties recur at regular intervals.

Based on this law, Mendeleev constructed his periodic table, arranging elements into horizontal periods by increasing atomic mass and vertical groups by similar properties. His table was revolutionary for its ability to systematically classify elements, predict the existence and properties of undiscovered elements (e.

g., Eka-aluminium, Eka-silicon), and correct the atomic masses of some known elements. However, it had limitations, including the ambiguous position of hydrogen, the inability to accommodate isotopes, the presence of anomalous pairs (e.

g., Ar-K, Te-I) where atomic mass order was violated, and the lack of a clear placement for lanthanides and actinides. Despite these demerits, Mendeleev's work laid the indispensable foundation for the modern periodic table and our understanding of elemental periodicity.

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Key Concepts

Periodicity and Chemical Properties

Mendeleev's genius lay in recognizing that chemical properties, particularly valency and the formulas of…

Predictive Power (Eka-elements)

One of the most celebrated aspects of Mendeleev's work was his ability to predict the existence and…

Anomalous Pairs and the Atomic Mass Limitation

While atomic mass was the basis of his law, it also led to some inconsistencies. Mendeleev sometimes had to…

Mendeleev's Law: — Properties are periodic function of atomic masses.

Basis: — Increasing atomic mass.

Merits:

- Systematic classification. - Prediction of undiscovered elements (Eka-Al $ightarrow$ Ga, Eka-Si $ightarrow$ Ge). - Correction of atomic masses (e.g., Beryllium).

Demerits:

- Position of Hydrogen. - Position of Isotopes (different mass, same properties). - Anomalous Pairs (Ar-K, Te-I, Co-Ni). - No place for Lanthanides/Actinides. - No explanation for periodicity.

Groups: — Vertical columns (similar properties).

Periods: — Horizontal rows (increasing atomic mass).

My Periodic Law Always Makes Discoveries:

Mass-based (Atomic Mass)

Predicts elements (Eka-Al, Eka-Si)

Leaves gaps

Anomalous pairs (Ar-K, Te-I) - a Demerit

Mass corrections (Beryllium)

Difficult for isotopes & Hydrogen - also Demerits