The Question is from neet-chemistry , and it was created by the author THIRUPATHI REDDY

Question

Mendeleef’s Periodic Table is upset by the fact that

THIRUPATHI REDDY · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
	**Primary Concept**: Periodic Table and Periodic Trends
	**Related Topics**: Atomic Weight, Chemical Properties, Periodicity
	**Prerequisites**: Basic understanding of the periodic table and its organization.
## SOLUTION PATHWAY
Mendeleev arranged elements primarily by increasing atomic weight, but he also considered their chemical properties. In some cases, he had to switch the order of elements based on their properties to maintain periodicity. This means arranging elements solely by atomic weight sometimes led to discrepancies in the observed trends of properties.

## OPTION ANALYSIS
[A] ✓: Arranging elements solely by increasing atomic weight leads to some elements being out of order in terms of their properties. This is the correct answer. Mendeleev recognized that certain elements, like tellurium and iodine, needed to be placed out of order based on atomic weight to fit properly with their chemical families.  For example, tellurium (atomic weight 127.6) is placed before iodine (atomic weight 126.9) because tellurium's properties are more similar to those of oxygen and sulfur, while iodine's are more similar to those of fluorine and chlorine.
[B] :x: The discovery of noble gases completely disrupted the order of the periodic table. This is incorrect. While the noble gases were unknown to Mendeleev initially, their discovery did not disrupt the existing order. They were added as a new group (Group 18) without affecting the arrangement of the other elements.  Their inert nature also fit well with the periodic trends.
[C] :x: Elements with similar atomic weights always have similar properties. This is incorrect.  This statement is contradicted by several examples in the periodic table.  Cobalt and nickel have very similar atomic weights but distinct chemical properties.  The same is true for many other pairs of elements.
[D] :x: Mendeleev did not account for the existence of isotopes. This is incorrect, but not the primary reason for the 'upset'. While Mendeleev's table did not initially account for isotopes, their discovery later explained some of the minor discrepancies in atomic weights. Isotopes of an element have different atomic weights but the same chemical properties, so their discovery refined, rather than disrupted, the periodic table.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing atomic weight with atomic number: Remember that Mendeleev's table was based on atomic weight, while the modern periodic table is based on atomic number.
		2. Assuming the periodic table was perfect from the start: The periodic table has undergone several revisions and improvements since its initial conception.
	**Quick Tips**:
		1. Remember the key exceptions to the atomic weight order in Mendeleev's table (e.g., tellurium and iodine).
		2. Focus on the relationship between chemical properties and the arrangement of elements in the periodic table.

THIRUPATHI REDDY · Answer

The correct Option is "Arranging elements solely by increasing atomic weight leads to some elements being out of order in terms of their properties."

THIRUPATHI REDDY · Answer

The discovery of noble gases completely disrupted the order of the periodic table.

THIRUPATHI REDDY · Answer

Elements with similar atomic weights always have similar properties.

THIRUPATHI REDDY · Answer

Mendeleev did not account for the existence of isotopes.

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