The elements of Group 1 and Group 2 of the modern periodic table are called S-block elements. Two types of s block elements are possible, i.e., the elements with one electron (s1) or the elements with two electrons (s2) in their s-subshell.
Table of Contents
What Are S-Block Elements?
S-block elements having only one electron in their s-orbital are called group one or alkali metals, whereas the s block elements having two electrons filling their s-orbital are called group two or alkaline earth metals.
The electrons present in an atom occupy various sub-orbitals of available energy levels in the order of increasing energy. The last electron of an atom may find itself in either of the s, p, d and f subshells. Accordingly, the elements of the atom having their last valence electron present in the s-suborbital are called s block elements.
Electronic Configuration of S-Block Elements
The electronic configuration of S-block elements is explained below.
The alkali elements in the s-block consist of a single valence electron in their outermost shell. This outermost electron is loosely held, which makes these metals highly electropositive. Due to this, they are not available in a free state in nature. The general electronic configurations of s block elements – group 1 are as shown in the table below:
Element
Symbol
Electronic Configuration
Lithium
Li
1s22s1
Sodium
Na
1s22s22p63s1
Potassium
K
1s22s22p63s23p64s1
Rubidium
Rb
1s22s22p63s23p63d104s24p65s1
Caesium
Cs
[Xe]6s1
Francium
Fr
[Rn]7s1
The electronic configurations of elements included in group 2 of S block elements are shown below:
Elements
Symbols
Electronic Configuration
Beryllium
Be
[He]2s2
Magnesium
Mg
[Ne]3s2
Calcium
Ca
[Ar]4s2
Strontium
Sr
[Kr]5s2
Barium
Ba
[Xe]6s2
Radium
Ra
[Rn]7s2
Properties of S-Block Elements
Both alkali and alkaline earth elements show a regular gradation in their properties among their respective group elements. But the first member of both S block elements, namely, Lithium and Beryllium, differ much from the rest of their members, but at the same time, they resemble more with the diagonal element present in the next column.
The anomaly of these S-block elements is due to the following:
Low atomic and ionic size
Greater charge density (charge/volume of the atom)
Greater polarization
Absence of d-orbitals.
Greater polarization of s block elements makes the first element more covalent and differentiates them from the rest, which is ionic.
The similarity in size and charge density makes them resemble the element diagonally placed in the next group (diagonal relationship).
It is observed that the physical and chemical properties of these s block elements change in a particular trend as the atomic number of the elements increases. Changes in the various properties of the group are as mentioned below:
Chemical Properties of s Block Elements
Atomic and Ionic Radii
When the s block elements of the modern periodic table are observed, it is seen that the size of the alkali metals is larger compared to other elements in a particular period. As the atomic number increases, the total number of electrons increases along with the addition of shells.
On moving down the group, the atomic number increases. As a result, the atomic and ionic radius of the alkali metals increases.
Ionization Enthalpy
As we go down the group, the size of the atoms increases, due to which the attraction between the nucleus and the electrons in the outermost shell decreases. As a result, the ionization enthalpy decreases. The ionization enthalpy of the alkali metals is comparatively lesser than other elements.
Hydration Enthalpy
As the ionic sizes of the elements increase, the hydration enthalpy decreases. The smaller the size of the ion, the hydration enthalpy is high as the atom has the capacity to accommodate a larger number of water molecules around it due to the high charge/radius ratio, and hence gets hydrated.
Physical Properties of s Block elements
In the s block elements, the density of the alkali metals increases down the group. Exception: the density of potassium is less than the density of sodium.
Alkali metals have a low melting and boiling point due to weak metallic bonding.
Alkali metals and their respective salts have the capability to impart colour to the oxidizing flame due to the heat generated from the flame, which excites the valence electrons from one energy level to another energy level. This helps in the detection of alkali metals during the flame test.
Diagonal Relationship within s Block Elements
A diagonal relationship in s block elements exists between adjacent elements, which are located in the second and third periods of the periodic table. For example, the lithium of group 1A and the second period shows similarities with the properties of magnesium, which are located in the 2nd group and 3rd period.
Similarly, the properties of beryllium, which are located in the 2nd group and 2nd periods, show a likeness with the properties of aluminium which is located in the third period and third group. The two elements which show similarities in their properties can be called diagonal pairs or diagonal neighbours.
The properties of s block elements vary significantly when compared to the other elements of the sub-group they belong to. The diagonal neighbours show a lot of similarities. Such a relationship is exhibited as you move left to the right and down the group; the periodic table has opposing factors.
For example, the electronegativity of the s block elements increases as we go across the period and decreases as we go down the group. Therefore, when it is moved diagonally, the opposite tendencies cancel out, and the value of electronegativity almost remains the same.
Similarities between Lithium and Magnesium
The hardness of lithium and magnesium is higher than the other elements in their respective groups.
Chlorides of lithium and magnesium have the capability to be soluble in ethanol.
They are lighter when compared to other elements in their groups.
Lithium and magnesium react gently with water. The oxides and hydroxides are less soluble.
In the presence of nitrogen, lithium and magnesium form their respective nitrides.
Superoxides are not formed when lithium and magnesium react with excess oxygen.
Carbon dioxide and its respective oxides are formed when carbonates of magnesium and lithium are heated.
Similarities between Beryllium and Aluminium
Aluminium hydroxide and beryllium hydroxide react with excess alkali to form their respective ions.
Both these elements have the capacity to withstand the acid attack due to the presence of an oxide film on the surface of the metal.
Chlorides of both these metals possess the capacity to be soluble in organic solvents.
Frequently Asked Questions on s Block Elements
Q1
The first member of the s block elements differs from the rest of their members considerably. Why?
Lithium and beryllium, the first members of the s-block family, differ much from the rest of their members. The anomaly of these elements is due to their,
Low atomic and ionic size
Greater charge density (charge/volume of the atom)
Greater polarization
Absence of ’d’ orbitals.
Greater polarization makes the first element form covalent compounds compared to the rest, which are ionic.
Q2
Will there be any difference in properties between oxides of 1st group sodium and caesium and 2nd group magnesium and barium compounds? Give an example.
Sodium and magnesium form oxides with lower oxidation numbers, while heavier atoms form oxides with higher oxidation numbers. Sodium forms oxide and peroxide, whereas oxygen has an oxidation number of -2 and -1, respectively.
In magnesium oxide, oxygen is in a -2 state. But caesium forms super-oxides where the oxidation state of oxygen is – 0.5. Similarly, the heavier barium form peroxide, having an oxidation state of oxygen as -1.
Q3
Covalent beryllium sulphate is soluble in water, while ionic barium sulphate is insoluble in water. Why?
Solubility depends on two factors:
Breaking of bonds to form ionic entities
The energy of solvation (hydration energy) of the entities through ionic interactions.
Covalent compounds like beryllium sulphate have a higher enthalpy of dissociation than ionic barium sulphate. But the smaller entities like beryllium have higher charge density, resulting in higher solvation, and hence, the release of hydration enthalpy is larger than the dissociating energy.
So, BeSO4 is more soluble than ionic BaSO4.
Q4
S block elements are prepared by electrolysis and not by the reduction of their compounds by other group elements or their compounds. Which is the strongest reducing agent?
S-block elements are strong electropositive elements with low reduction potential, indicating their strong reducing ability compared to others. So, substances having lower reducing ability than them will not be able to reduce them. Reducing the ability of an atom is related to the ease of releasing electrons for reduction. Decreasing ionization energy down the column suggests that caesium is a stronger reducing agent than Lithium.
But, reducing ability (oxidation potential) depends on the combined energy difference of three processes:
Sublimation of the atom
Ionization of the metal ion
Hydration of the ion with water
Lithium, being the smallest ion, its hydration enthalpy is very high than caesium and compensates more than its higher ionization enthalpy. Thus, lithium has the highest reducing ability (highest oxidation potential or lowest reduction potential = -3.04V) compared to caesium.
Q5
Is there an easy way to identify the presence of the s block elements?
S block elements, or their halides on exposure to flame, undergo electronic transitions in the visible region of the light spectrum. Hence, they induce characteristic colour into the flame. The colours are as follows:
Metals
Lithium
Sodium
Potassium
Rubidium
Caesium
Flame colour
Crimson red
Yellow
Violet
Red violet
Blue
Metals
Beryllium
Magnesium
Calcium
Strontium
Barium
Flame colour
–
–
Brick red
Crimson red
Apple green
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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