NCERT Class 11 Chemistry Classification of Elements and Periodicity In Properties

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Classification Of Elements And Periodicity In Properties Class 11 Chemistry NCERT

Class 11 Chemistry students should refer to the following NCERT Book chapter Classification Of Elements And Periodicity In Properties in standard 11. This NCERT Book for Grade 11 Chemistry will be very useful for exams and help you to score good marks

Classification Of Elements And Periodicity In Properties NCERT Class 11

 

CLASSIFICATION OF ELEMENTS AND

PERIODICITY IN PROPERTIES

In this Unit, we will study the historical development of the Periodic Table as it stands today and the Modern Periodic Law. We will also learn how the periodic classification follows as a logical consequence of the electronic configuration of atoms. Finally, we shall examine some of the periodic trends in the physical and chemical properties of the elements.

3.1 WHY DO WE NEED TO CLASSIFY ELEMENTS ?

We know by now that the elements are the basic units of all types of matter. In 1800, only 31 elements were known. By 1865, the number of identified elements had more than doubled to 63. At present 114 elements are known. Of them, the recently discovered elements are man-made. Efforts to synthesise new elements are continuing. With such a large number of elements it is very difficult to study individually the chemistry of all these elements and their innumerable compounds individually. To ease out this problem, scientists searched for a systematic way to organise their knowledge by classifying the elements. Not only that it would rationalize known chemical facts about elements, but even predict new ones for undertaking further study.

3.2 GENESIS OF PERIODIC CLASSIFICATION

Classification of elements into groups and development of Periodic Law and Periodic Table are the consequences of systematising the knowledge gained by a number of scientists through their observations and experiments. The German chemist, Johann Dobereiner in early 1800’s was the first to consider the idea of trends among properties of elements.

By 1829 he noted a similarity among the physical and chemical properties of several groups of three elements (Triads). In each case, he noticed that the middle element of each of the Triads had an atomic weight about half way between the atomic weights of the other two (Table 3.1). Also the properties of the middle element were in between those of the other two members. Since Dobereiner’s relationship, referred to as the Law of Triads, seemed to work only for a few elements, it was dismissed as coincidence. The next reported attempt to classify elements was made by a French geologist, A.E.B. de Chancourtois in 1862.

He arranged the then known elements in order of increasing atomic weights and made a cylindrical table of elements to display the periodic recurrence of properties. This also did not attract much attention. The English chemist, John Alexander Newlands in 1865 profounded the Law of Octaves. He arranged the elements in increasing order of their atomic weights and noted that every eighth element had properties similar to the first element (Table 3.2). The relationship was just like every eighth note that resembles the first in octaves of music. Newlands’s Law of Octaves seemed to be true only for elements up to calcium.

Although his idea was not widely accepted at that time, he, for his work, was later awarded Davy Medal in 1887 by the Royal Society, London. The Periodic Law, as we know it today owes its development to the Russian chemist, Dmitri Mendeleev (1834-1907) and the German chemist, Lothar Meyer (1830-1895). Working independently, both the chemists in 1869 proposed that on arranging elements in the increasing order of their atomic weights, similarities appear in physical and chemical properties at regular intervals. Lothar Meyer plotted the physical properties such as atomic volume, melting point and boiling point against atomic weight and obtained a periodically repeated pattern. Unlike Newlands, Lothar Meyer observed a change in length of that repeating pattern. By 1868, Lothar Meyer had developed a table of theelements that closely resembles the Modern Periodic Table. However, his work was not published until after the work of Dmitri Mendeleev, the scientist who is generally credited with the development of the Modern Periodic Table.


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Chapter 1 Some Basic Concepts of Chemistry
NCERT Class 11 Chemistry Some Basic Concepts Of Chemistry
Chapter 2 Structure of Atom
NCERT Class 11 Chemistry Structure of Atom
Chapter 3 Classification of Elements and Periodicity in Properties
NCERT Class 11 Chemistry Classification of Elements and Periodicity In Properties
Chapter 4 Chemical Bonding and Molecular Structure
NCERT Class 11 Chemistry Chemical Bonding and Molecular Structure
Chapter 5 States of Matter
NCERT Class 11 Chemistry State Of Matter
Chapter 6 Thermodynamics
NCERT Class 11 Chemistry Thermodynamics
Chapter 7 Equilibrium
NCERT Class 11 Chemistry Equilibrium
Chapter 8 Redox Reactions
NCERT Class 11 Chemistry Redox Reactions
Chapter 9 Hydrogen
NCERT Class 11 Chemistry Hydrogen
Chapter 10 The s-Block Elements
NCERT Class 11 Chemistry The s Block Elements
Chapter 11 The p-Block Elements
NCERT Class 11 Chemistry The p Block Elements
Chapter 12 Organic Chemistry – Some Basic Principles & Techniques
NCERT Class 11 Chemistry Organic Chemistry Some Basic Priciples and Techniques
Chapter 13 Hydrocarbons
NCERT Class 11 Chemistry Hydrocarbons
Chapter 14 Environmental Chemistry
NCERT Class 11 Chemistry Environmental Chemistry
Other Chapters
NCERT Class 11 Chemistry Lab Manual Titrimetric Analysis
NCERT Class 11 Chemistry Lab Manual Chemical Equilibrium Ionic Equilibrium
NCERT Class 11 Chemistry Lab Manual Information about Investigatory Projects
NCERT Class 11 Chemistry Lab Manual Introduction
NCERT Class 11 Chemistry Lab Manual ph and ph change in Aqueous Solutions
NCERT Class 11 Chemistry Lab Manual Purification and Criteria of Purity
NCERT Class 11 Chemistry Lab Manual Systematics Qualitative Analysis
NCERT Class 11 Chemistry Lab Manual Basic Laboratory Techniques
Part I Answer to Some Selected Problems
NCERT Class 11 Chemistry Answer of Some Selected Problems
Part I Appendices
NCERT Class 11 Chemistry Appendix 5 Some Useful Conversion Factores
NCERT Class 11 Chemistry Appendix 6 Thernodynamic Data at 298 K
NCERT Class 11 Chemistry Appendix 7 Standard Potentials at 298 K in Electrochemical order
NCERT Class 11 Chemistry Appendix 1
NCERT Class 11 Chemistry Appendix 2 Elements Their Atomic Number and Molar Mass
NCERT Class 11 Chemistry Appendix 3
NCERT Class 11 Chemistry Appendix 4 Physical Constants
Part II Answer to Some Selected Problems
NCERT Class 11 Chemistry Answer to Some Selected Problems

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