The Question is from neet-chemistry classification-of-elements-and-periodicity-in-prop , and it was created by the author Mr. S M HUSSAIN

Question

Which of the following pairs of elements would have been placed in the SAME group in Mendeleev's periodic table but DIFFERENT groups in the modern periodic table?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
	**Primary Concept**: Mendeleev's Periodic Table vs. Modern Periodic Table
	**Related Topics**: Periodic trends, Group classification, Atomic weight vs. Atomic number
	**Prerequisites**: Basic understanding of periodic table organization.
## SOLUTION PATHWAY
**Given Information**:
	Pairs of elements and the question of their grouping in Mendeleev's and the Modern Periodic Table.
**Method & Steps**:
	1. **Mendeleev's Table**: Elements were arranged based on increasing atomic weight and similar chemical properties.
		Reasoning: Mendeleev prioritized chemical properties over strict atomic weight order in some cases to ensure elements with similar reactivity fell within the same group.
	2. **Modern Periodic Table**: Elements are arranged based on increasing atomic number (number of protons) and electronic configuration, which dictates chemical properties.
		Working: The modern periodic table reflects the periodic recurrence of similar electronic configurations, leading to predictable trends in chemical properties.
	3. **Analyzing the pairs**: We need to find a pair placed in the same group by Mendeleev (similar properties) but separated in the modern table (different electronic configurations/group numbers).
		Result: Tellurium (Te) and Iodine (I) fit this description.
		Verification: Mendeleev placed Te (127.6 amu) before I (126.9 amu) due to Te's properties being more similar to elements in group 16 (chalcogens like sulfur and selenium). The modern table places I in group 17 (halogens) and Te in group 16 based on atomic number (52 for Te and 53 for I) and electronic configurations.
## OPTION ANALYSIS
[A] ✓: Tellurium (Te) and Iodine (I) - As explained above, Mendeleev placed these together based on properties, while the modern table separates them based on atomic number and electronic configuration.
[B] :x: Sodium (Na) and Potassium (K) - Both are alkali metals and reside in the same group in both periodic tables.
[C] :x: Calcium (Ca) and Magnesium (Mg) - Both are alkaline earth metals and reside in the same group in both periodic tables.
[D] :x: Iron (Fe) and Cobalt (Co) - These transition metals are adjacent in both tables, although their precise placement within the d-block might have subtle differences based on electron filling rules, they were broadly in the same 'group' (as understood in Mendeleev's time) due to similar properties.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing atomic weight with atomic number: Remember Mendeleev used weight, while the modern table uses number.
		2. Overlooking the importance of chemical properties in Mendeleev's classification: He prioritized chemical similarities even if it meant slightly deviating from strict atomic weight order.
	**Quick Tips**:
		1. Remember the Te/I anomaly as a classic example of the difference between the two tables.
		2. Visualize the periodic table and the positions of the elements to reinforce your understanding of group classifications.

Mr. S M HUSSAIN · Answer

The correct Option is "Tellurium (Te) and Iodine (I)"

Mr. S M HUSSAIN · Answer

Sodium (Na) and Potassium (K)

Mr. S M HUSSAIN · Answer

Calcium (Ca) and Magnesium (Mg)

Mr. S M HUSSAIN · Answer

Iron (Fe) and Cobalt (Co)

NEET Chemistry Classification of Elements and Periodicity in Properties MCQs

Select Topic

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

NEET Subjects

Our Bots

Company