Periodic Classification of Elements refers to the arrangement of elements on the basis of the periodic repetition of their properties. It means the elements which exhibit similar properties on a regular interval are placed in the same group.
Table of Contents
Classification of Elements
Elements are the basic units that make up all matter in our surroundings. Earlier, only 31 chemical elements were discovered in 1800. Around 63 new elements were discovered in 1865.
This necessitated the periodic classification of elements as it was difficult to remember the properties of each element. Hence, if we put all the alike elements in the same group we can predict the properties of each element of that group. There are presently 118 elements that we are aware of.
History of Classification of Elements
The Periodic Table which we learn today is not the result of a single effort. There have been several attempts in the past to classify elements, however, few got succeed and even these tables had some drawbacks and hence were revised by new classifications.
Hence, the Modern Periodic table evolved over the period. Some of the successful attempts to classify elements are listed below:
Dobernier Triad
Newland Law of Octaves
Lother Meyer Arrangement
Mendleeves Periodic Table
Modern Periodic Table
Dobernier Triad
In 1829, Dobernier attempted the first-ever classification of elements. He placed 3 elements in a group and stated that the mass of the middle element is equal to the arithmetic mean of the other two elements. He made 3 such groups. The group formed by him is shown below:
In the first group, the atomic mass of Li is 7 and K is 39. If we find the mean of atomic masses of Li and K it will be (7 + 39)/2 = 46/2 = 23 which is the atomic mass of Sodium. This property was followed in the three groups formed.
Drawbacks of Dobernier’s Triad
The drawbacks of the Dobernier’s Triads are discussed below,
Dobernier could only form three such triads out of 30 elements that were known at that time.
Dobernier Triad was not applicable to very low or very high atomic mass elements
In the case of F, Cl, and Br, the rule of arithmetic mean is not valid, although F, Cl, and Br are placed in the same order in the modern periodic table.
Newland Law of Octaves
Newland, a British Chemist made an attempt in 1865 to arrange atoms in increasing order of their atomic mass. He stated that when atoms are arranged on the basis of increasing order of the mass then every eighth element exhibits similar properties. This arrangement was based on his understanding of musical notes where the word repeats after every 7th interval. It is similar to Indian Musical Note Sa, Re, Ga, Ma…..
The elements arranged in Newlands law of Octaves are discussed in the image below,
Drawbacks of Newland Law of Octaves
The drawbacks of the Newland Law of Octaves are discussed below,
It was applicable only to Calcium. After Calcium, every eighth element didn’t resemble the properties.
Dissimilar elements were placed in the same group while similar atoms were placed in different groups. For Example, Iron was placed with Oxygen and Sulphur.
Some groups contain two elements in one place. For Example, Co & Ni.
Lother Meyer’s Arrangement
In 1869, Lother Meyer a German Chemist stated that when elements are arranged in order of increasing atomic mass then elements exhibit similar properties at regular intervals.
Mendleeve’s Periodic Table
Mendeleev in the same year 1869 unknown of the Lother Meyer’s arrangement gave the most successful and detailed periodic table. He stated that “The properties of elements whether physical or chemical are periodic functions of their atomic masses”. Based on his law he arranged all the attempts known at that time in a table called the Periodic Table, which later on became the basis of the arrangement of elements for the Modern Periodic Table. He called the vertical column ‘Groups’ and horizontal rows ‘Periods’.
Features of Mendeleeve’s Periodic Table
Important features of Mendeleeve’s Periodic Table are listed below:
It was the most simplified arrangement of elements based on their properties. One can easily guess the property of elements placed in a particular group.
He corrected the atomic masses of elements such as Beryllium, Gold, Indium, etc.
He left vacant positions for some elements that were not known at that time but he predicted such elements would exist in the future. He added the prefix ‘eka’ to those elements. For Example, Eka Aluminium was Gallium, Eka-Silicon was Germanium.
Drawbacks of Mendeleeve’s Periodic Table
Following are the drawbacks of Mendeleeve’s Defect
The position of Hydrogen was not defined. Hydrogen resembles properties with that of alkali metals as well as halogens but was placed in the group of alkali metals. He couldn’t explain why hydrogen will not be in the halogen group although both are nonmetals.
There exists anomalous pair in the table which would not follow the law of increasing atomic weight. For Example, Argon (39.9 u) was placed before K (39.1) and Co was placed before Ni.
Since the table was based on increasing order of atomic mass but the position of isotopes was not defined as isotopes have different masses.
The position of Lanthanoids and Actinoids was not assigned separately.
Similar atoms were placed in different groups while dissimilar atoms were placed in the same groups. For example, Alkali Metals Li, Na, and K were placed together with Cu, Ag, and Au, even though their properties are quite dissimilar.
Modern Periodic Table
Modern Periodic Table is a long-form periodic classification of elements based on the electronic configuration of elements. Modern Periodic Table has vertical columns called ‘Groups’ and horizontal rows called ‘Periods’. There are 18 Groups and 7 Periods in Modern Periodic Table. The Modern Periodic Table was given by Henry Mosley in 1913.
Features of Modern Periodic Table
The following are the properties of the Modern Periodic Table:
It is based on the atomic number of elements rather than atomic mass.
Since it is based on atomic numbers hence it solved the problem of the position of isotopes.
It allows systematic classification of Elements on the basis of s, p, d, and f on the basis of the subshell in which the last electron enters.
In Modern Periodic Table Metals are on Left Hand Side while Non-Metals are on Left Hand Side. The two sides are connected by d-block elements also known as transition elements
The elements which formed anomalous pairs in Mendeleeve’s Periodic Table got their justified position in this table as the classification is based on atomic number rather than atomic mass.
Lanthanoid and Actinoids were placed in the table separately at the bottom.
It accomodated much larger number of elements and even have spaces for elements which can be discovered in future. Presently there are 118 elements in the table.
Drawbacks of Modern Periodic Table
Although Modern Periodic Table solves all the issues of Mendeleeve’s classification yet it has some drawbacks:
The position of Hydrogen is still not settled as Hydrogen resembles properties of both halogen and Alkali Metals.
Lanthanoids and Actinoids are placed separately at the bottom and are not part of main table.
Modern Periodic Law
Modern Periodic Law became the basis of the Modern Periodic Table. It was given by Henry Mosely in 1913. It states that
Elements’ physical and chemical properties are periodic functions of their atomic numbers and not atomic mass.
Classification of the Elements in the Periodic Table
The elements in the periodic table can be classified in four ways based on their electronic configurations:
Noble gas elements: Noble gases are elements in the modern periodic table’s group 18. The electronic configuration of this group’s first element (helium) is 1s2. The rest of the elements (neon, argon, krypton, xenon, and radon) have an ns2 np6 outer shell electronic configuration. Since the octet of these elements is complete, they are extremely stable.
Representative elements: S-block and p-block elements are examples of representative elements. The elements in groups 1 and 2 are referred to as s – block elements (elements with 1s2 and 2s2 outermost configuration). Groups 13-17 are known as the p-block elements (outermost configuration varies from ns2 np1 to ns2 np5).
Transition elements: Transition elements are elements that belong to groups 3 to 12 and have an outer shell electronic configuration of (n-1)d1-10 ns1-2. These elements are also referred to as d-block elements.
Inner transition elements: The inner transition elements are the lanthanides and actinides series, which are found at the bottom of the periodic table. The 4f and 5f orbitals are partially filled in these elements, giving them unique properties.
Alkali and Alkaline Earth metals: The first two groups on the periodic table’s left side are made up of highly reactive elements (except hydrogen). The Elements of the first group are called Alkali Metals, while the elements of the second group are called Alkaline Earth Metals
Metalloids and non-metals: Metalloids are typically found in a diagonal line on the periodic table’s right side. These are the elements that separate metals on the left side of the periodic table from non-metals on the right. Because these elements have properties of both metals and nonmetals, they are referred to as metalloids.
Some General Trends of Periodicity in Modern Periodic Table
Atomic Radius: It is the distance from the center of the nucleus to the valence shell of the atom. In Modern Periodic Table, Atomic Radius decreases as we go left to right in a period, and the atomic radius increases as we go down the group.
Ionization Potential: It is the ability of an atom to lose electrons from its valence shell. Higher Ionization Potential means difficult to lose electrons while lower ionization potential means easy to lose electrons. As we go down the group ionization potential decreases and as we move left to right in a group ionization potential increases.
Electronegativity: It refers to the ability of shared pairs of electrons by an element in a molecule. Electronegativity decreases as we go down the group and increases as we move left to right in a period. The most electronegative elements are F > O > N.
Metallic Character: Metals are elements that lose electrons and gain positive charge. The ability to lose electrons is given by ionization potential. Hence as we go down the group metallic character increases and as we move left to right in a period metallic character decreases.
Note: It should be noted that the above trend in properties is general in nature. There exist exceptions in between which we will discuss later.
FAQs on Periodic Classification of Elements
Q1: How many Elements are there in Periodic Table?
Answer:
There are 118 elements in Modern Periodic Table.
Q2: Why do we need Periodic Classification of Elements?
Answer:
As there are large number of elements it is difficult to remember properties of each element, hence,we need Periodic Classification of Elements to understand the properties in a more better and efficient way.
Q3: What are the Limitations of the Dobernier Triads?
Answer:
Dobernier Triad was valid for only 9 elements out of 30 elements available at that time. Also it was not valid for very high and low atomic masses of elements.
Q4: What is Modern Periodic Law?
Answer:
Modern Periodic Law states that the physical and chemical properties of elements is a function atomic number of elements and not atomic mass.
Q5: How does Atomic Radius vary in Periodic Table?
Answer:
In Periodic Table, atomic radius increases down the group and increases on moving left to right across periods.
Neeraj Anand, Param Anand
Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations.
In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS".
He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.
CBSE Class 11 Chemistry Syllabus is a vast which needs a clear understanding of the concepts and topics. Knowing CBSE Class 11 Chemistry syllabus helps students to understand the course structure of Chemistry.
Unit-wise CBSE Class 11 Syllabus for Chemistry
Below is a list of detailed information on each unit for Class 11 Students.
UNIT I – Some Basic Concepts of Chemistry
General Introduction: Importance and scope of Chemistry.
Nature of matter, laws of chemical combination, Dalton’s atomic theory: concept of elements, atoms and molecules.
Atomic and molecular masses, mole concept and molar mass, percentage composition, empirical and molecular formula, chemical reactions, stoichiometry and calculations based on stoichiometry.
UNIT II – Structure of Atom
Discovery of Electron, Proton and Neutron, atomic number, isotopes and isobars. Thomson’s model and its limitations. Rutherford’s model and its limitations, Bohr’s model and its limitations, concept of shells and subshells, dual nature of matter and light, de Broglie’s relationship, Heisenberg uncertainty principle, concept of orbitals, quantum numbers, shapes of s, p and d orbitals, rules for filling electrons in orbitals – Aufbau principle, Pauli’s exclusion principle and Hund’s rule, electronic configuration of atoms, stability of half-filled and completely filled orbitals.
UNIT III – Classification of Elements and Periodicity in Properties
Significance of classification, brief history of the development of periodic table, modern periodic law and the present form of periodic table, periodic trends in properties of elements -atomic radii, ionic radii, inert gas radii, Ionization enthalpy, electron gain enthalpy, electronegativity, valency. Nomenclature of elements with atomic number greater than 100.
UNIT IV – Chemical Bonding and Molecular Structure
Valence electrons, ionic bond, covalent bond, bond parameters, Lewis structure, polar character of covalent bond, covalent character of ionic bond, valence bond theory, resonance, geometry of covalent molecules, VSEPR theory, concept of hybridization, involving s, p and d orbitals and shapes of some simple molecules, molecular orbital theory of homonuclear diatomic molecules(qualitative idea only), Hydrogen bond.
UNIT V – Chemical Thermodynamics
Concepts of System and types of systems, surroundings, work, heat, energy, extensive and intensive properties, state functions. First law of thermodynamics – internal energy and enthalpy, measurement of U and H, Hess’s law of constant heat summation, enthalpy of bond dissociation, combustion, formation, atomization, sublimation, phase transition, ionization, solution and dilution. Second law of Thermodynamics (brief introduction) Introduction of entropy as a state function, Gibb’s energy change for spontaneous and nonspontaneous processes. Third law of thermodynamics (brief introduction).
UNIT VI – Equilibrium
Equilibrium in physical and chemical processes, dynamic nature of equilibrium, law of mass action, equilibrium constant, factors affecting equilibrium – Le Chatelier’s principle, ionic equilibrium- ionization of acids and bases, strong and weak electrolytes, degree of ionization, ionization of poly basic acids, acid strength, concept of pH, hydrolysis of salts (elementary idea), buffer solution, Henderson Equation, solubility product, common ion effect (with illustrative examples).
UNIT VII – Redox Reactions
Concept of oxidation and reduction, redox reactions, oxidation number, balancing redox reactions, in terms of loss and gain of electrons and change in oxidation number, applications of redox reactions.
UNIT VIII – Organic Chemistry: Some basic Principles and Techniques
General introduction, classification and IUPAC nomenclature of organic compounds. Electronic displacements in a covalent bond: inductive effect, electromeric effect, resonance and hyper conjugation. Homolytic and heterolytic fission of a covalent bond: free radicals, carbocations, carbanions, electrophiles and nucleophiles, types of organic reactions.
UNIT IX – Hydrocarbons
Classification of Hydrocarbons Aliphatic Hydrocarbons: Alkanes – Nomenclature, isomerism, conformation (ethane only), physical properties, chemical reactions. Alkenes – Nomenclature, structure of double bond (ethene), geometrical isomerism, physical properties, methods of preparation, chemical reactions: addition of hydrogen, halogen, water, hydrogen halides (Markovnikov’s addition and peroxide effect), ozonolysis, oxidation, mechanism of electrophilic addition. Alkynes – Nomenclature, structure of triple bond (ethyne), physical properties, methods of preparation, chemical reactions: acidic character of alkynes, addition reaction of – hydrogen, halogens, hydrogen halides and water.
Aromatic Hydrocarbons:
Introduction, IUPAC nomenclature, benzene: resonance, aromaticity, chemical properties: mechanism of electrophilic substitution. Nitration, sulphonation, halogenation, Friedel Craft’s alkylation and acylation, directive influence of functional group in monosubstituted benzene. Carcinogenicity and toxicity.
To know the CBSE Syllabus for all the classes from 1 to 12, visit the Syllabus page of CBSE. Meanwhile, to get the Practical Syllabus of Class 11 Chemistry, read on to find out more about the syllabus and related information in this page.
CBSE Class 11 Chemistry Practical Syllabus with Marking Scheme
In Chemistry subject, practical also plays a vital role in improving their academic scores in the subject. The overall weightage of Chemistry practical mentioned in the CBSE Class 11 Chemistry syllabus is 30 marks. So, students must try their best to score well in practicals along with theory. It will help in increasing their overall academic score.
CBSE Class 11 Chemistry Practical Syllabus
The experiments will be conducted under the supervision of subject teacher. CBSE Chemistry Practicals is for 30 marks. This contribute to the overall practical marks for the subject.
The table below consists of evaluation scheme of practical exams.
Evaluation Scheme
Marks
Volumetric Analysis
08
Salt Analysis
08
Content Based Experiment
06
Project Work
04
Class record and viva
04
Total
30
CBSE Syllabus for Class 11 Chemistry Practical
Micro-chemical methods are available for several of the practical experiments. Wherever possible such techniques should be used.
A. Basic Laboratory Techniques 1. Cutting glass tube and glass rod 2. Bending a glass tube 3. Drawing out a glass jet 4. Boring a cork
B. Characterization and Purification of Chemical Substances 1. Determination of melting point of an organic compound. 2. Determination of boiling point of an organic compound. 3. Crystallization of impure sample of any one of the following: Alum, Copper Sulphate, Benzoic Acid.
C. Experiments based on pH
1. Any one of the following experiments:
Determination of pH of some solutions obtained from fruit juices, solution of known and varied concentrations of acids, bases and salts using pH paper or universal indicator.
Comparing the pH of solutions of strong and weak acids of same concentration.
Study the pH change in the titration of a strong base using universal indicator.
2. Study the pH change by common-ion in case of weak acids and weak bases.
D. Chemical Equilibrium One of the following experiments:
1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of either of the ions. 2. Study the shift in equilibrium between [Co(H2O)6] 2+ and chloride ions by changing the concentration of either of the ions.
E. Quantitative Estimation i. Using a mechanical balance/electronic balance. ii. Preparation of standard solution of Oxalic acid. iii. Determination of strength of a given solution of Sodium hydroxide by titrating it against standard solution of Oxalic acid. iv. Preparation of standard solution of Sodium carbonate. v. Determination of strength of a given solution of hydrochloric acid by titrating it against standard Sodium Carbonatesolution.
F. Qualitative Analysis 1) Determination of one anion and one cation in a given salt Cations‐ Pb2+, Cu2+, As3+, Al3+, Fe3+, Mn2+, Ni2+, Zn2+, Co2+, Ca2+, Sr2+, Ba2+, Mg2+, NH4+ Anions – (CO3)2‐ , S2‐, NO2‐ , SO32‐, SO2‐ , NO ‐ , Cl‐ , Br‐, I‐, PO43‐ , C2O2‐ ,CH3COO‐ (Note: Insoluble salts excluded)
2) Detection of ‐ Nitrogen, Sulphur, Chlorine in organic compounds.
G) PROJECTS Scientific investigations involving laboratory testing and collecting information from other sources.
A few suggested projects are as follows:
Checking the bacterial contamination in drinking water by testing sulphide ion
Study of the methods of purification of water.
Testing the hardness, presence of Iron, Fluoride, Chloride, etc., depending upon the regional variation in drinking water and study of causes of presence of these ions above permissible limit (if any).
Investigation of the foaming capacity of different washing soaps and the effect of addition of Sodium carbonate on it.
Study the acidity of different samples of tea leaves.
Determination of the rate of evaporation of different liquids Study the effect of acids and bases on the tensile strength of fibres.
Study of acidity of fruit and vegetable juices.
Note: Any other investigatory project, which involves about 10 periods of work, can be chosen with theapproval of the teacher.
Practical Examination for Visually Impaired Students of Class 11
Below is a list of practicals for the visually impaired students.
A. List of apparatus for identification for assessment in practicals (All experiments) Beaker, tripod stand, wire gauze, glass rod, funnel, filter paper, Bunsen burner, test tube, test tube stand, dropper, test tube holder, ignition tube, china dish, tongs, standard flask, pipette, burette, conical flask, clamp stand, dropper, wash bottle • Odour detection in qualitative analysis • Procedure/Setup of the apparatus
B. List of Experiments A. Characterization and Purification of Chemical Substances 1. Crystallization of an impure sample of any one of the following: copper sulphate, benzoic acid B. Experiments based on pH 1. Determination of pH of some solutions obtained from fruit juices, solutions of known and varied concentrations of acids, bases and salts using pH paper 2. Comparing the pH of solutions of strong and weak acids of same concentration.
C. Chemical Equilibrium 1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of eitherions. 2. Study the shift in equilibrium between [Co(H2O)6]2+ and chloride ions by changing the concentration of either of the ions.
D. Quantitative estimation 1. Preparation of standard solution of oxalic acid. 2. Determination of molarity of a given solution of sodium hydroxide by titrating it against standard solution of oxalic acid.
E. Qualitative Analysis 1. Determination of one anion and one cation in a given salt 2. Cations – NH+4 Anions – (CO3)2-, S2-, (SO3)2-, Cl-, CH3COO- (Note: insoluble salts excluded) 3. Detection of Nitrogen in the given organic compound. 4. Detection of Halogen in the given organic compound.
Note: The above practicals may be carried out in an experiential manner rather than recording observations.
We hope students must have found this information on CBSE Syllabus useful for their studying Chemistry. Learn Maths & Science in interactive and fun loving ways with ANAND CLASSES (A School Of Competitions) App/Tablet.
Frequently Asked Questions on CBSE Class 11 Chemistry Syllabus
Q1
How many units are in the CBSE Class 11 Chemistry Syllabus?
There are 9 units in the CBSE Class 11 Chemistry Syllabus. Students can access various study materials for the chapters mentioned in this article for free at ANAND CLASSES (A School Of Competitions).
Q2
What is the total marks for practicals examination as per the CBSE Class 11 Chemistry Syllabus?
The total marks for the practicals as per the CBSE Class 11 Chemistry Syllabus is 30. It includes volumetric analysis, content-based experiment, salt analysis, class record, project work and viva.
Q3
Which chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry?
The organic chemistry chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry.
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