Group 13 elements are the first group in the p-block of the periodic table. All the elements of group 13 are also called the boron family. The periodic table is segregated into s, p, d and f-blocks. This segregation is done based on the valence electron; if the valence electron falls on the p subshell, it comes in the p-block and so on.
The members of Group 13 elements are as follows:
Boron
Aluminium
Gallium
Indium
Thallium
The general electronic configuration for the group 13 elements is ns2 np1.
Table of Contents
Oxidation States and Inert Pair Effect
The general oxidation state exhibited by the group 13 elements in the group are +3 and +1. As we go down the group of the Boron family, the tendency to form +1 ion increases. This is due to the inert pair effect.
To elucidate, consider B3+ and B+. It is shown experimentally that B3+ is more stable than B+. Now, consider, Tl3+ and Tl+. It was seen that Tl+ is more stable than Tl3+.
This can be explained using the inert pair effect. It is the non-participation of the s-orbital during chemical bonding due to the poor shielding of the intervening electrons.
Simply put, for elements like Indium and Thallium, d and f orbitals are filled with electrons. Since the shielding ability of d and f orbitals are very poor, the nuclear charge that seeps through attracts the s orbital closer to the nucleus. This makes the s orbital reluctant to bond, thereby, only the p electrons are involved in bonding.
Covalent Character of Group 13 Elements
There are three reasons for the formation of covalent compounds by group 13 elements.
Fajan’s rule may be applied. The smaller the cation, the more is the covalence.
They have very high ionisation enthalpies ( IE1+IE2+IE3), which makes the formation of ionic compounds hard.
They have relatively higher electronegativities, and hence the formation of compounds would not result in a higher electronegativity difference.
Reasons Behind the Anomalous Behaviour of Boron
Boron behaves differently from the rest of the elements present in group 13 because of the following reasons:
It has a very small size
It has very high ionisation enthalpy
It has high electronegativity owing to its small size
The absence of d-orbital in the valence shell
Chemical Properties of Group 13 Elements
Reactivity of Group 13 towards Oxygen
All of the elements of group 13 react at high temperatures forming trioxides, M2O3.
4M(s) + O2 (g) → 2M2O3(s)
Tl, besides forming Tl2O3, forms Tl2O.
The reactivity of group 13 elements towards oxygen increases down the group.
Boron is unreactive towards oxygen in its crystalline form. Finely divided amorphous boron reacts with oxygen on heating to form B2O3.
Thermodynamically, aluminium should react with air, but it is stable. This is because Al2O3 forms as a protective layer on the surface of the metal, thereby making it inert.
Reactivity of Group 13 towards Acids and Alkalis
Boron does not react with non-oxidising acids like HCl, but at higher temperatures, it reacts with strong oxidizing acids like a mixture of hot concentrated H2SO4 and HNO3 to give boric acid.
B(s) + 3HNO3 (aq) → H3BO3 (aq) + 3NO2 (g)
Boron resists the action of alkalis (NaOH and KOH) up to 773 K, above which they form borates.
2B(s) + 6KOH(s) → 2K3BO3(s) + 3H2(g)
All the other elements of group 13 react both with non-oxidising and oxidising acids, liberating hydrogen gas.
Note: The action of concentrated HNO3 renders Aluminium and Gallium passive by forming a protective layer of oxide.
Aluminium and Gallium can also react with alkalis liberating hydrogen gas.
They react with halogens at high temperatures to form trihalides MX3.
2M(s) + 3X2 (g) → 2MX3 (where X=F,Cl,Br,I)
Tl, however, only forms TlF3 and TlCl3.
Note: Tl also forms mono-halides.
Reactivity of Group 13 towards Water and Metals
Reactivity towards Water :
Boron does not react with water or steam; however, at very high temperatures, it reacts with steam.
2B + 3H2O → B2O3 + 3H2
If the oxide layer is absent, Aluminium decomposes in cold water to yield hydrogen gas. Gallium and Indium do not react with water unless oxygen gas is present. Thallium forms TlOH in moist air.
4Tl + 2H2O + O2 → 4TlOH
Reactivity towards Metals:
Only boron combines with metals to form borides. The rest of the elements of group 13 are reluctant to combine with metals. This portrays the non-metallic character of Boron.
3Mg + 2B → Mg3B2
Complex Forming Tendency
Group 13 elements have more tendency to form complexes than s-block elements due to their smaller size and more polarising power.
Boron can form many complexes like [BF4]–. It has sp3 hybridized orbitals and tetrahedral geometry. Other elements also form complex compounds like Li[AlH4], [GaCl6]3-.
Physical Properties of Group 13 Elements
Atomic and Ionic Radii
The atomic radii of group 13 elements are lesser than their corresponding group 2 elements. This is because the effective nuclear charge increases which makes the size of the atom smaller.
The atomic and ionic radii down the group increase due to the addition of a new shell. There is a deviation, however, on moving from Aluminium (143 pm) to Gallium (135 pm). This arises due to the poor shielding of the intervening d-orbitals in Gallium, making the size smaller than Aluminium.
Boron< Aluminium > Gallium < Indium< Thallium
Ionization Energy
Down the group, the values of Ionization Enthalpy do not decrease smoothly. From Boron to Aluminium, the Ionization Enthalpy increases as expected. But from Aluminium to Gallium, the Ionization Enthalpy increase slightly. The first Ionization Enthalpy of Thallium is greater than Aluminium.
Reason: This trend is observed due to the poor shielding of d and f orbitals. Gallium is smaller than Aluminium due to poor d shielding; therefore, IE1 of Aluminium < IE1 of Gallium. Similarly, Thallium has intervening f orbitals, which are very poor at shielding, thereby increasing the IE1 of Thallium.
Element
IE1 (KJmol-1)
B
801
Al
577
Gallium
579
In
558
Tl
589
Electronegativity
The electronegativity first decreases from B to Al, then it increases slightly from Aluminium to Tl. This can be attributed to the poor shielding of the intervening d and f orbitals.
Electropositivity
The trend expected should be the exact opposite of electronegativity. The metallic character first increases from B to Al, then it decreases slightly from Aluminium to Tl.
This is due to the fact that Group 13 has a very high Ionization Enthalpy. Also, the larger the size of the ion, the lesser is its Ionization Enthalpy. Therefore, Aluminium is the most metallic. This can further be explained using the standard reduction potentials.
Element
B
Al
Ga
In
Tl
M3+(aq)/M(s)
-0.87
-1.66
-0.56
-0.34
+1.26
This shows that Aluminium is the most metallic and that Tl3+ isn’t that stable, as the potential is positive, making Gibb’s free energy positive. (∆G = -nFE).
Density
The elements of group 13 have higher densities than group 2 elements. This is because they have smaller sizes, and hence small volumes. The density increases from B to Tl.
Acid-Base Characteristics
The acidic character of oxides of group 13 elements decreases down the group, and the basic character increases.
Note: Both Al and Gallium are amphoteric in nature.
H3BO3 is a monobasic acid in water. This is because water acts as a Lewis base, and H3BO3 acts as a Lewis acid. This results in the release of a proton,
B (OH) 3 + H2O ↔ [B (OH) 4] – + H+
Compounds of Group 13 Elements
Oxides
All the elements of group 13 form sesquioxides (sesqui means one and a half). The formula of the oxide formed is MO3/2 or M2O3.
B2O3 is formed by heating amorphous boron in air,
4B + 3O2 → 2B2O3
Boron suboxide (BO) 2 is formed by heating B2O3 with boron at 1050°C.
B + B2O3 → (BO) 2
The oxides of the other elements can be prepared by the thermal decomposition of their nitrates or their hydroxides.
2Al (OH) 3 → Al2O3 + 3H2O
Halides
Boron forms trihalides with Fluorine, Chlorine, and Iodine. All of the trihalides formed are planar molecules and sp2 hybridized.
Since all the elements of group 13 possess only 6 electrons in their valance shell, they act as Lewis acids.
The order of the Lewis acid character exhibited by the trihalides is,
BBr3>BCl3>BF3
Reason: This is not in accordance with the normal trend observed; surely, we can claim that BF3 is the most acidic as F is the most electronegative.
The reason for the above trend is back bonding, specifically, pπ-pπ back bonding. The lone pair on F is given to the empty p-orbital of B, making it less electropositive and, thereby, reducing the acidic character.
The overlap of B and F is maximum as their sizes are compatible. Boron cannot form effective back bonding with Cl or Br as they are bigger than B. The halides of Al, Gallium, In and Tl are largely covalent.
Borates
Borates are compounds of group 13 containing discrete [BO3]3- units. Each unit is sp2 hybridized. They are classified according to the way the individual units are linked.
Orthoborates: They contain discrete BO33- units. For example, Mg3(BO3)2.
Pyroborates: Two units of BO33- are linked via a common oxygen atom. The formula is B2O54-. For example, Mg2B2O5.
Metaborates: They have a structure where each unit shares two oxygen atoms. Therefore, they are either in the form of chains or cyclic. The general formula is (BO2)nn-.
Sheet borate: The two-dimensional network of borates where all three oxygen atoms are shared.
Boron Hydrides
The binary compounds formed by boron and hydrogen are called boranes. The simplest borane known is B2H6. They are classified into three major types,
Closo-boranes ( BnH2n+2)
Nido-boranes (BnH2n+4)
Arachno-boranes (BnH2n+6)
Diborane (B2H6)
It can be prepared by reacting BCl3 with hydrogen gas over a Cu-Al catalyst at 450°C.
2BCl3 + 6H2 → B2H6 + 6HCl
Diborane on heating alone or in the presence of hydrogen, higher boranes are obtained.
Structure of Diborane
The total number of valence electrons present in diborane = 3 × 2 + 1 × 6 = 12 electrons.
The number of valence electrons in ethane (C2H6) = 4 × 2 + 1 × 6 = 14 electrons.
Therefore, we can see that diborane is electron deficient, and hence should be unstable.
From the data obtained from electron diffraction studies, we were able to elucidate the structure of diborane.
It has two types of hydrogen atoms, terminal and bridged. The four terminal B-H bonds have the same bond length, and they are normal covalent bonds.
The two bridged hydrogen atoms, however, the H-B-H bond, are much longer than the terminal B-H bond. The H-B-H bond is unusual as the two bridges involve only one electron from each hydrogen atom giving a total of four electrons. That is, each H-B-H bond has two electrons delocalized over three centres, giving rise to a three-centred two-electron bond.
Borazine
Boron-Nitrogen species that carry only one substituent on each atom and exist as trimers are called Borazine (B3N3H6).
It is prepared by heating diborane and ammonia in a 1:2 molar ratio at -120°C, which gives ionic species which, on heating, give borazine.
B2H6 + 2NH3 → [H2B(NH3)2]+[BH4]– → B3N3H6 + 6H2
Similarities of Borazine with Benzene
Borazine is isoelectric with benzene, i.e., the total number of electrons in benzene = 6 × 6 + 1 × 6 = 42 electrons and the total number of electrons in borazine = 3 × 5 + 3 × 7 + 6 × 1 = 42 electrons.
Borazine is isosteric with benzene. That is, the total number of atoms are the same.
Borazine possesses a cyclic structure of alternating boron and nitrogen atoms.
Both N and B are sp2 hybridized.
Properties of Borazine
It readily undergoes an addition reaction. This is because the B-N bond is polar, unlike the covalent C-C bond, and hence addition reactions happen easily.
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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