Chalcogens are the Group 16 elements of the modern periodic table consisting of 5 elements oxygen, sulphur, selenium, tellurium and polonium. The elements in this group are also known as chalcogens or ore-forming elements because many elements can be extracted from sulphide or oxide ores. The chalcogens are the elements that belong to group 16 of the modern periodic table (or the oxygen family).
In this article, we are going to learn about what are chalcogens, elements under the chalcogen family and their properties in detail.
Table of Contents
What are Chalcogens?
Group 16 elements also called Chalcogens are the elements in the oxygen family. They are a group of five elements: oxygen, sulfur, selenium, tellurium, and polonium. Sometimes oxygen is excluded from the chalcogen family for generalizing the chemical properties of the group. The chemical properties of oxygen are quite different from the other members of the group.
The synthetic element Livermorium (symbol Lv) is also considered a part of the chalcogen family.
How to Isolate Chalcogens?
To isolate elements of chalogens various methods are used that include,
Oxygen is one of the largest constituent of air and separation of air results in the formation of oxygen and nitrogen.
We can easily extract Sulfur from natuarla oil and petroleum.
Tellurium and Selenium are produced as the byproduct of refining of copper.
Particle accelerators is used to create Livermorium and Polonium.
Elements of Chalcogen (Oxygen) Family
In the modern periodic table, Chalcogens is composed of five elements: oxygen, sulphur, selenium, tellurium, and polonium. Oxygen is abundant on the planet. When the proportions of different types of atoms found in the universe were calculated, oxygen was determined to be the fourth most abundant element after hydrogen, helium, and neon. It constitutes about 89% of water, 46% of the earth’s crust and 20 % of the air.
Electronic Configuration of Chalcogen Family
The symbol, atomic number and electronic configuration of elements of Chalcogens are given below in this article.
Oxygen
O
8
[He] 2s2 2p4
Sulphur
S
16
[Ne] 3s2 3p4
Selenium
Se
34
[Ar] 3d10 4s2 4p4
Tellurium
Te
52
[Kr] 4d10 5s2 5p4
Polonium
Po
84
[Xe]4f14 5d10 6s2 6p4
Now let’s learn about them in detail.
Oxygen
Oxygen is denoted by the symbol O. It is a colourless and odourless gas that is converted into carbon dioxide during the human respiration process. Oxygen is a diatomic molecule. Oxygen is also found in trace amounts as a triatomic molecule (O3), which is known as ozone. Many elements combine easily with oxygen. The evolution of heat energy occurs during the combination of some elements; this process is known as combustion.
Sulphur
Symbol S represents sulfur. It’s a nonmetal that ranks ninth in terms of cosmic abundance. Sulphur can be found in both the combined and free states. Sulfates account for about 0.09 per cent of the sulphur found in seawater. The meteorite contains 12% sulphur, and a significant amount of sulphur is found in underground deposits of pure sulphur present in dome-like structures. Sulphur is formed in this environment by the action of anaerobic bacteria on sulphate minerals such as gypsum.
Selenium
Selenium is rarer than oxygen or sulphur. It can be found in a few minerals both free and combined with heavy metals (such as lead, silver, or mercury). Under typical settings, the grey metallic form of selenium is the most stable form of the element.
Tellurium
Tellurium is a chemical element with the atomic number 52 and properties intermediate between metals and nonmetals. It is one of the earth’s crust’s rarest stable elements. It is frequently found in its free state as well as in compounds with elements such as copper, lead, silver, and gold.
Polonium
It is the rarest element in the group of sixteen elements. It is a radioactive substance. Polonium is occasionally used in alpha radiation applications in science.
Physical Properties of Group 16 Elements (Chalcogens Family)
Some important physical properties of Group 16 elements are:
Electronic Configuration
Atomic/Ionic Radii
Ionization Enthalpies
Electron Gain Enthalpies
Electronegativities
Metallic Nature
Melting and Boiling Points
Now, we will study them in detail.
Electronic Configuration
Group 16 elements or elements of the oxygen family have six electrons in their outermost shell. So the general electronic configuration of them is ns2, np4. Electronic configuration of each member of the oxygen family is,
Oxygen(O)
[He] 2s2 2p4
Sluphur(S)
[Ne] 3s2 3p4
Selenium(Se)
[Ar] 3d10 4s2 4p4
Tellurium(Te)
[Kr] 4d10 5s2 5p4
Polonium(Po)
[Xe]4f14 5d10 6s2 6p4
Atomic/Ionic Radii of Group 16 Elements
Atomic radii or ionic radii of elements increase as they move down the periodic table. The chalcogen with the smallest atomic and ionic radius (excluding livermorium) is oxygen, and the chalcogen with the largest (excluding livermorium) is polonium. The addition of protons and the increase in effective nuclear charge cause elements’ atomic radii to decrease over time. As a result, the atomic radius of oxygen will be much smaller than that of lithium.
Ionization Enthalpies of Group 16 Elements
Ionization Enthalpies of the elements of the oxygen family are less compared to those of the nitrogen family. The general trend of moving down the group from oxygen to polonium, suggests that the ionization enthalpy or potential decreases on moving down the group.
On moving left to right the general trend of the ionization enthalpy suggest that it increases along the period.
Electron Gain Enthalpies of Group 16 Elements
Electron Gain Enthalpies decrease with an increase in the atom’s size. As a result, the electron gain enthalpies of the chalcogens decrease as one moves down the group. It is worth noting that oxygen has a lower negative electron gain enthalpy than sulphur, which can be attributed to the compressed atomic structure of oxygen, which contributes to interelectronic repulsion between the valence electrons and any other approaching electron.
Electronegativities of Group 16 Elements
Electronegativity decreases as one moves down a group due to a variety of factors, including an increase in atomic radius and an increase in electron-electron repulsion. The most electronegative chalcogen is oxygen, and the least electronegative chalcogen is polonium (livermorium not considered).
Metallic Nature of Group 16 Elements
Non-metal elements include oxygen and sulphur. Metalloids include selenium and tellurium. Under normal conditions, polonium has metallic properties. It should be noted, however, that polonium is a radioactive element.
Melting and Boiling Points of Group 16 Elements
Melting and Boiling points of elements increase as they progress down a group due to the increase in atomic sizes and atomic masses (as a result of increased intermolecular forces of attraction). Among chalcogens, oxygen has the lowest melting and boiling points. The significant difference in the melting and boiling points of sulphur and oxygen can be attributed to the fact that oxygen exists in the atmosphere as a diatomic molecule, whereas sulphur is typically found as a polyatomic molecule.
Note:
Fluorine is the most electronegative element while Oxygen is the second most electronegative element.
All the members of group 16 i.e. oxygen family exhibit allotropy.
Sulphur(S) in the oxygen family show catenation property similar to that of carbon.
Chemical Properties of Group 16 Elements
Some important chemical properties of Group 16 elements are:
Allotropes
Oxidation States
Reactions with Hydrogen
Now, we will study them in detail.
Allotropes
Almost all chalcogens have multiple allotropes. The most common oxygen allotropes are dioxygen and ozone. In fact, there are nine known allotropes of oxygen. Furthermore, there are over 20 known allotropes of sulphur. Selenium is known to have at least five different allotropes, while polonium is known to have two. Monoclinic sulphur and rhombic sulphur are the two most stable allotropic forms of sulphur. It should be noted that selenium and tellurium are both crystalline and amorphous elements.
Oxidation States
Because the chalcogens’ general electronic configuration is ns2 np4, they can achieve a stable electronic configuration by gaining two electrons or participating in covalent bonding. When they gain two electrons, the ion formed has the general formula M2- (where M denotes a chalcogen). The chalcogens exhibit regular oxidation states of -2, +2, +4, and +6.
Reactions with Hydrogen
When chalcogens react with dihydrogen, they usually form hydrides with the general formula H2M (where M can be any chalcogen – oxygen, sulphur, selenium, tellurium, or polonium). This chemical reaction takes the following general form:
M (chalcogen) + H2 (dihydrogen) → H2M (hydride of the chalcogen)
Chemistry of Livermorium
Livermorium with atomic number Z=116 is the newest member of the Oxygen family. In the May of 2012, IUPAC approved the name “Livermorium” (symbol Lv) for the element with atomic number 116 which becomes the newest member of the Group 16 elements. It is a heavy element and is radioactive in nature.
FAQs on Group 16 Elements (Chalcogens Family)
1. What are Elements of Chalcogens in Chemistry?
There are five elements that come under Chalcogen in Chemistry and that include,
Oxygen
Sulphur
Selenium
Tellurium
Polonium
2. What is the Nature of Chalcogens?
Non-metal elements include oxygen and sulphur. Metalloids are elements like selenium and tellurium. Under normal circumstances, polonium has metallic properties. It’s worth noting, though, that polonium is a radioactive element.
3. What happens to Ionization Energy of Chalcogens as we move Down the Group?
Ionisation Enthalpy reduces as radius of atom increases (it is easier to remove an electron from an atom with a large atomic radius since the distance between the nucleus and the valence shell will be relatively large). Thus, the ionization energy of chalcogens drops down as we move down the group.
4. What happens to Electronegativity of Chalcogens as we move Down the Group?
As we move down the group the electronegativity of chalcogens decreases. Oxygen is the most electronegative chalcogen, while polonium is the least electronegative.
5. Is Polonium a Radioactive Element? What is it used for?
Yes, Polonium a radioactive element, it is used as a fuel in nuclear reactor and nuclear bomb.
6. Which is Most Volatile Hydride of Chalcogens?
The most volatile hydride of the oxygen family is H2Te
7. What is Correct Order of Acidity of Hydrides of Chalcogens?
The correct order of acidity of hydrides of the oxygen family is,
H2Te > H2Se > H2S > H2O
8. Why Group 16 Elements are called Chalcogens?
Group 16 elements are also called Chalcogens. The term “Chalcogen” is derived from Greek word “chalkos” meaning “ore” as these compounds are formed as the ores of various compounds they are called the chalcogens.
9. What are Chalcogens in Perdioic Table?
Chalcogens in the periodic table is the other name of Group 16 elements.
10. What are Chalcogen Elements?
The chalcogen elements are, Oxygen, Sulfur, Selenium, Tellurium, and Polonium
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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