Chapter 5: Periodic Classification of elements Class 10 Science NCERT – Chapterwise Important Questions & Answers for CBSE Exam Preparation
Class 10 Science Chapter 5: Periodic Classification of elements NCERT Important Questions and Answers for CBSE
Chapter 5: Periodic Classification of elements
1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table. [SEBA 2018]
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
Answer : (b) The number of valence electrons increases.
2. Element X forms a chloride with the formula 
, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as [SEBA 2019]
(a) Na (b) Mg (c) AI (d) Si
Answer : (b) Mg
1. Answer Yes, Döbereiner's triads also existed in the columns of Newlands' Octaves. Both Döbereiner and Newlands were early attempts at classifying elements based on their properties.
Döbereiner's triads grouped three elements with similar chemical properties, and their atomic weights showed a pattern where the middle element's atomic weight was approximately the average of the other two. For example, lithium (Li), sodium (Na), and potassium (K) form a triad with atomic weights: Li (6.9), Na (23), and K (39). The atomic weight of Na (23) is close to the average of Li (6.9) and K (39).
Newlands' Octaves, on the other hand, attempted to classify elements in groups of eight. He noticed that every eighth element had similar properties, which he referred to as "octaves." However, this pattern worked only up to a certain point and did not cover the entire periodic table.
2. Answer : Döbereiner's classification had some limitations:
Limited triads: Not all elements could be grouped into triads, as some elements didn't fit well with others in terms of properties and atomic weights.
Incomplete ordering: Döbereiner's classification didn't cover all known elements at that time, leaving gaps in the periodic table.
Lack of a pattern: There was no clear pattern or explanation for why certain elements formed triads while others didn't.
Ignored other properties: Döbereiner only focused on chemical properties and atomic weights, ignoring other important characteristics of elements.
Not universally applicable: The triads concept worked well only for a few elements and couldn't be extended to all elements known at that time.
These limitations led to the development of more comprehensive periodic table systems, such as Mendeleev's Periodic Table, which addressed these issues and provided a more robust and systematic organization of elements.
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