2 marksShort AnswerSection SECTION A

State the criteria used by Mendeleev for creating his Periodic Table. Compare the position of isotopes of elements in the Mendeleev's Periodic Table and in the Modern Periodic Table.

Q: State the criteria used by Mendeleev for creating his Periodic Table. Compare the position of isotopes of elements in the Mendeleev's Periodic Table and in the Modern Periodic Table.

### Criteria used by Mendeleev for creating his Periodic Table: 1. **Atomic Mass:** Mendeleev arranged the elements in the increasing order of their atomic masses. 2. **Chemical Properties:** He grouped elements based on the similarities in their chemical properties, specifically focusing on the formulae of the hydrides and oxides formed by the elements. ### Comparison of the Position of Isotopes: - **In Mendeleev's Periodic Table:** Since Mendeleev's classification was based on increasing atomic masses, isotopes of an element (which have different atomic masses but identical chemical properties) posed a major challenge. They would logically require separate positions based on their masses, but this would violate their chemical grouping. Hence, no separate or satisfactory position could be assigned to isotopes. - **In the Modern Periodic Table:** In the Modern Periodic Table, elements are arranged in the increasing order of their atomic numbers ($Z$). Since all isotopes of a given element have the same atomic number, they are placed in the same position (same slot) in the table, resolving the anomaly completely.

Metals and Non-metals

Mendeleev's Periodic Table

Official Answer

Criteria used by Mendeleev for creating his Periodic Table:

Atomic Mass: Mendeleev arranged the elements in the increasing order of their atomic masses.
Chemical Properties: He grouped elements based on the similarities in their chemical properties, specifically focusing on the formulae of the hydrides and oxides formed by the elements.

Comparison of the Position of Isotopes:

In Mendeleev's Periodic Table: Since Mendeleev's classification was based on increasing atomic masses, isotopes of an element (which have different atomic masses but identical chemical properties) posed a major challenge. They would logically require separate positions based on their masses, but this would violate their chemical grouping. Hence, no separate or satisfactory position could be assigned to isotopes.
In the Modern Periodic Table: In the Modern Periodic Table, elements are arranged in the increasing order of their atomic numbers ( $Z$ ). Since all isotopes of a given element have the same atomic number, they are placed in the same position (same slot) in the table, resolving the anomaly completely.

atomic masschemical propertieshydridesoxidesisotopesatomic numbersame position

Marking Scheme

1State Mendeleev's criteria: Increasing atomic mass (0.5 mark) and similarity in chemical properties/formulae of oxides and hydrides (0.5 mark).
2Position of isotopes in Mendeleev's table: No separate/proper position could be given because they have different atomic masses (0.5 mark).
3Position of isotopes in Modern Periodic Table: Placed in the same position because they have the same atomic number (0.5 mark).

Hint

Think about what fundamental property Mendeleev used to arrange elements versus what property is used in the Modern Periodic Table, and how isotopes differ in these properties.

Quick Oral Answer

Mendeleev used atomic mass and chemical properties (like oxide/hydride formulae) to arrange elements. Isotopes have different atomic masses but the same atomic number. Therefore, they couldn't be placed properly in Mendeleev's table but are placed in the same slot in the Modern Periodic Table.

Analysis & Explanation

Mendeleev's Periodic Law states that the properties of elements are a periodic function of their atomic masses. This formulation meant that isotopes, discovered much later, could not be accommodated easily because isotopes of the same element (e.g., $^{35}\text{Cl}$ and $^{37}\text{Cl}$ ) have different atomic masses. If arranged strictly by mass, they should occupy different slots. However, they exhibit identical chemical behavior. The Modern Periodic Table, proposed by Henry Moseley, resolved this by using atomic number as the organizing principle. Since isotopes have the same number of protons (atomic number), they naturally occupy the exact same position in the Modern Periodic Table.

Common Mistakes

1Confusing atomic mass with atomic number when describing Mendeleev's criteria.
2Failing to mention the formulae of oxides and hydrides as the specific chemical properties Mendeleev studied.
3Stating that isotopes were placed in different groups in Mendeleev's table, whereas they actually had no defined place.

Interesting Facts

Mendeleev left empty spaces in his periodic table for elements that were yet to be discovered, such as Eka-boron, Eka-aluminium, and Eka-silicon, and predicted their properties with astonishing accuracy before they were even found!

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2022?

This question carries 2 marks in the CBSE Class 10 Science 2022 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Mendeleev's Periodic Table" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2022 paper?

This is a Short Answer question from Section SECTION A in the CBSE Class 10 Science 2022 paper.