The branch of chemistry deals with the study of carbon compounds. For example Methane, Ethane, Urea, DNA etc. It is not necessary that all carbon compounds are organic. Examples: Nitrogen, Halogen, Cyanide (CN-), Carbon dioxide, Amine (NH3) etc. Some naturally occurring organic compounds are present in plants and animals and in synthetic organic compounds from fossil fuels and plant materials.
The replacement of one or more hydrogen atoms of a hydrocarbon, aliphatic or aromatic, by an equal number of halogen atoms, results in the formation of alkyl halides (haloalkanes) and aryl halides (haloarenes) respectively. In haloalkanes, the halogen atom(s) is(are) attached to the sp3-hybridised carbon atom(s) of an alkyl group whereas, in haloarenes, the halogen atom(s) is(are) attached to sp2 -hybridised carbon atom(s) of an aryl group.
Table of Contents
Nomenclature of Haloalkanes (Alkyl Halides)
In general, the mono halogen derivatives of alkanes are called alkyl halides. The complete name of alkyl halide is written in two separate words. In the IUPAC system, the name of mono halogen derivatives of alkanes is given as haloalkanes. Their names are derived by prefixing the word ‘halo’ to the name of the longest straight chain alkane. The numbering of the parent straight chain of an alkane is done in such a manner that the carbon atom having the halogen atom gets the lowest possible number. The IUPAC name of any mono halogen derivative of an alkane is always written as one word.
Dihalogen derivatives: They are of three different types as-
Alkylidene dihalides- The di-haloalkanes are in which two halogen atoms of the same type are present on the same carbon atom and are called alkylidene dihalides. The positions on the same carbon atom are called geminal positions. For example, Dichloromethane or Methylene dichloride (CH2Cl2), 1,1-Dibromoethane or Methylene dichloride (CH3CHBr3), etc.
Alkylene dihalides- The di-halogen derivatives of alkanes in which the two halogen atoms of the same type are present on the adjacent carbon atoms of the carbon chain and are called alkylene dihalides. In the IUPAC system, the two halogen atoms are prefixed to the name of dihaloalkane. For example, 1,2-Dichloroethane or Ethylene dichloride (ClCH2CH2Cl), 1,2-Dibromoethane or Ethylene dibromide (BrCH2CH2Br), etc.
Polymethylene dihalides- In a common system, dihalogen derivatives of alkanes in which the same two halogen atoms are present on the terminal carbon atoms, i.e., α, ω-positions of the carbon chain are called polymethylene dihalides. In the IUPAC system, the halogen atoms are prefixed to the name of the dihaloalkane. For example, 1,3-Dibromopropane or Trimethylene dibromide (BrCH2CH2CH2Br), 1,4-dichlorobutane or Tetramethylene dichloride ( ClCH2CH2CH2CH2Cl), etc.
Polyhaloalkanes: In the common system, trihalomethanes and tetrahalomethanes are called haloforms and carbon tetrahalides respectively. For example, Trichloromethane or Chloroform (CHCl3), Tribromomethane or Bromoform (CHBr3), etc.
Nature of the C-X Bond
The nature of the C-X bond is different for Haloalkanes and Haloarenes, therefore both are discussed separately as:
Haloalkanes: Halogen atoms are more electronegative than carbon. Due to this, they share pair of electrons that lies closer to the halogen atom.
As a result, the halogen carries a small negative charge i.e. δ- while the carbon carries a small positive charge i.e. δ+. As we go down the periodic table, the size of the halogen atom increases. The fluorine atom is the smallest and the iodine atom is the largest. so the carbon-halogen bond length also increases C-F to C-I. Further, as we move from F to me, the electronegativity of the halogen decreases, therefore, the polarity of the C-X bond and hence dipole moment of the haloalkane should also decrease.
Haloarenes: In the case of haloarenes carbon of the benzene ring attached to a halogen is sp2 hybridised which have a short length and can hold more electron pair and the C-X bond is polar in nature. so the lone pair of electrons undergo the resonance with the benzene ring due to this delocalisation of the lone pair of electrons leading to the formation of double character.
Salient Features of the nature of C-X bond in Haloarenes and Haloalkanes
The C-X bond of haloalkanes is more polar than the C-X bond of haloarenes. This is due to the higher electronegativity of halogen over carbon.
There is a delocalized lone pair of electrons on the X atom present over the benzene ring which results in the double bond character in the C-X bond of haloarenes.
As we move in the periodic table the atomic size down the group increases hence C-X bond length in haloarenes also increases.
Also moving down the group the dipole moment decreases as the dipole moment depends on the electronegativity difference. As we know, Cl has less electronegativity than F, but the dipole moment of the C–Cl bond is more than C–F which is an exceptional case.
Parameters related to the Nature of the C-X bond
Bond Length – The bond length between the carbon and halogen group affect the nature of the C-X bond. As we move down the group the size of the halogen atom goes on increasing.
F < Cl < Br < I
So, the difference in C-F is the least and largest in the C-I bond.
Dipole moment – The general formula of dipole moment is μ = q × d, where ‘d’ is the distance or the charge separation between positive and negative charges. i.e. the dipole moment is the product of charge and distance and is the calculated polarity of chemical bond in the molecule.
So the order is:
CH3Cl > CH3F > CH3Br > CH3I
Bond Enthalpy – If we talk about the size of carbon and fluorine atoms then it is similar and there is an overlapping of orbitals that forms a very strong bond. But in the case of C-I, the size of the Iodine is large compared to that of carbon and can form a weak bond. So a large amount of energy is required to break the C-F bond then the C-I bond.
Here is the order of the bond enthalpy:
C-F > C-Cl > C-Br > C-I
Physical Data of important Halomethanes (CH3-X)
Halomethane
C-X bond length (pm)
C-X bond enthalpy (KJ mol-1)
Dipole moment (Debye)
CH3F
139
452
1.847
CH3Cl
178
351
1.860
CH3Br
193
293
1.830
CH3I
214
234
1.636
Uses of Halogen compounds are,
The chlorine-containing antibiotic is very effective for the treatment of typhoid fever.
Synthetic organic halogen compounds are extensively used in agriculture and industry.
For the treatment of malaria chloroquine (halogen compound) is used.
During surgery, halomethane is used as an anaesthetic.
Sample Questions(FAQs)
Question 1: Haloarenes are insoluble in water but are soluble in benzene, Explain.
Answer:
Haloarenes are insoluble in water because they cannot form hydrogen with water molecules. how ever, these are soluble in benzene in accordance with the general principle of solubility i.e., like dissolves like. Haloarenes are organic compounds having a large hydrocarbon part and are solutions in hydrocarbon solvents like benzene.
Question 2: The p-isomer of dichlorobenzene has a higher melting point than o- and m-isomer. Why?
Answer:
The melting point of para isomer is quite higher than that of ortho or meta isomers. This is due to that it has a symmetrical structure and therefore, its molecules can easily pack closely in crystal lattices as a result intermolecular forces of attraction are stronger and therefore, greater energy is required to 88 its lattice and its melts at a higher temperature.
Question 3: Iodoform gives a precipitate with silver nitrate on heating while chloroform does not. Explain.
Answer:
The Carbon-iodine bond is quite weak (213.4 KJ mol-1) as compared to the carbon-chlorine bond (326.4 KJ mol-1) Therefore, when the iodoform is heated with AgNO3 solution, C-l bond gets cleaved easily and iodide reacts with AgNO3 solution to give a precipitate of Agl. On the other hand, the C-Cl bond does not get dissolve.
Question 4: Organic halogen compounds used in industry as solvents are chlorides rather than bromides and iodides. Explain.
Answer:
Organic alkyl chlorides are used in industry as solvents because chlorides are more volatile than bromides and iodides.
Question 5: Chloroform contains chlorine but gives no reaction with AgNO3 solution. Why?
Answer:
CHCl2 contains chlorine but it is bonded to carbon by a covalent bond and therefore, it is not ionised. Hence, it does not combine with AgNO2 solution.
CHCl2 + AgNO2 ⇢ No reaction
Question 6: Why is chloroform stored in dark coloured bottles?
Answer:
Chloroform is oxidised to poisonous phosgene in the presence of air as,
CHCl2 + 1/2O2 ⇢COCl2 + HCl
Therefore, to protect it from light, chloroform is stored in dark coloured bottles.
Question 7: A small amount of ethyl alcohol is usually added to chloroform bottles. Why?
Answer:
Alcohol retards the oxidation of chloroform to phosgene and it converts phosgene to ethyl carbonate.
2C2H5OH + COHCl2 ⇢ (C2H6)2CO3 + 2 HCl
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.
Below is the CBSE Class 12 Syllabus along with the marking scheme and time duration of the Chemistry exam.
S.No
Title
No. of Periods
Marks
1
Solutions
10
7
2
Electrochemistry
12
9
3
Chemical Kinetics
10
7
4
d -and f -Block Elements
12
7
5
Coordination Compounds
12
7
6
Haloalkanes and Haloarenes
10
6
7
Alcohols, Phenols and Ethers
10
6
8
Aldehydes, Ketones and Carboxylic Acids
10
8
9
Amines
10
6
10
Biomolecules
12
7
Total
70
CBSE Class 12 Chemistry Practical Syllabus along with Marking Scheme
The following is a breakdown of the marks for practical, project work, class records, and viva. The total number of marks for all parts is 15. The marks for both terms are provided in the table below.
Evaluation Scheme for Examination
Marks
Volumetric Analysis
08
Salt Analysis
08
Content-Based Experiment
06
Project Work and Viva
04
Class record and Viva
04
Total
30
CBSE Class 12 Chemistry Syllabus (Chapter-wise)
Unit -1: Solutions
Raoult's law.
Colligative properties - relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmotic pressure, determination of molecular masses using colligative properties, abnormal molecular mass.
Solutions, Types of solutions, expression of concentration of solutions of solids in liquids, solubility of gases in liquids, solid solutions.
Van't Hoff factor.
Unit -2: Electrochemistry
Redox reactions, EMF of a cell, standard electrode potential
Nernst equation and its application to chemical cells
Relation between Gibbs energy change and EMF of a cell
Kohlrausch's Law
Electrolysis and law of electrolysis (elementary idea)
Dry cell-electrolytic cells and Galvanic cells
Conductance in electrolytic solutions, specific and molar conductivity, variations of conductivity with concentration.
Lead accumulator
Fuel cells
Unit -3: Chemical Kinetics
Rate of a reaction (Average and instantaneous)
Rate law and specific rate constant
Integrated rate equations and half-life (only for zerfirst-order order reactions)
Concept of collision theory (elementary idea, no mathematical treatment)
Factors affecting rate of reaction: concentration, temperature, catalyst;
Order and molecularity of a reaction
Activation energy
Arrhenius equation
Unit -4: d and f Block Elements
Lanthanoids- Electronic configuration, oxidation states, chemical reactivity and lanthanoid contraction and its consequences.
Actinoids- Electronic configuration, oxidation states and comparison with lanthanoids.
General introduction, electronic configuration, occurrence and characteristics of transition metals, general trends in properties of the first-row transition metals – metallic character, ionization enthalpy, oxidation states, ionic radii, color, catalytic property, magnetic properties, interstitial compounds, alloy formation, preparation and properties of K2Cr2O7 and KMnO4.
Unit -5: Coordination Compounds
Coordination compounds - Introduction, ligands, coordination number, color, magnetic properties and shapes
The importance of coordination compounds (in qualitative analysis, extraction of metals and biological system).
IUPAC nomenclature of mononuclear coordination compounds.
Bonding
Werner's theory, VBT, and CFT; structure and stereoisomerism
Unit -6: Haloalkanes and Haloarenes
Haloarenes: Nature of C–X bond, substitution reactions (Directive influence of halogen in monosubstituted compounds only). Uses and environmental effects of - dichloromethane, trichloro methane, tetrachloromethane, iodoform, freons, DDT.
Haloalkanes: Nomenclature, nature of C–X bond, physical and chemical properties, optical rotation mechanism of substitution reactions.
Unit -7: Alcohols, Phenols and Ethers
Phenols: Nomenclature, methods of preparation, physical and chemical properties, acidic nature of phenol, electrophilic substitution reactions, uses of phenols.
Ethers: Nomenclature, methods of preparation, physical and chemical properties, uses.
Alcohols: Nomenclature, methods of preparation, physical and chemical properties (of primary alcohols only), identification of primary, secondary and tertiary alcohols, mechanism of dehydration, and uses with special reference to methanol and ethanol.
Unit -8: Aldehydes, Ketones and Carboxylic Acids
Carboxylic Acids: Nomenclature, acidic nature, methods of preparation, physical and chemical properties; uses.
Aldehydes and Ketones: Nomenclature, nature of carbonyl group, methods of preparation, physical and chemical properties, mechanism of nucleophilic addition, the reactivity of alpha hydrogen in aldehydes, uses.
Unit -9: Amines
Diazonium salts: Preparation, chemical reactions and importance in synthetic organic chemistry.
Amines: Nomenclature, classification, structure, methods of preparation, physical and chemical properties, uses, and identification of primary, secondary and tertiary amines.
Unit -10: Biomolecules
Proteins -Elementary idea of - amino acids, peptide bond, polypeptides, proteins, structure of proteins - primary, secondary, tertiary structure and quaternary structures (qualitative idea only), denaturation of proteins; enzymes. Hormones - Elementary idea excluding structure.
Vitamins - Classification and functions.
Carbohydrates - Classification (aldoses and ketoses), monosaccharides (glucose and fructose), D-L configuration oligosaccharides (sucrose, lactose, maltose), polysaccharides (starch, cellulose, glycogen); Importance of carbohydrates.
Nucleic Acids: DNA and RNA.
The syllabus is divided into three parts: Part A, Part B, and Part C. Part A consist of Basic Concepts of Chemistry, which covers topics such as atomic structure, chemical bonding, states of matter, and thermochemistry. Part B consists of Topics in Physical Chemistry, which includes topics such as chemical kinetics, equilibrium, and electrochemistry. Part C consists of Topics in Organic Chemistry, which covers topics such as alkanes, alkenes, alkynes, and aromatic compounds.
Basic Concepts of Chemistry:
Atomic structure: This section covers the fundamental concepts of atomic structure, including the electronic configuration of atoms, the Bohr model of the atom, and the wave nature of matter.
Chemical bonding: This section covers the different types of chemical bonds, including ionic, covalent, and metallic bonds, as well as the concept of hybridization.
States of the matter: This section covers the three states of matter - solid, liquid, and gas - and the factors that influence their properties.
Thermochemistry: This section covers the principles of thermochemistry, including the laws of thermodynamics and the concept of enthalpy.
Chapters in Physical Chemistry:
Chemical kinetics: This section covers the study of the rate of chemical reactions and the factors that influence it, including the concentration of reactants, temperature, and the presence of catalysts.
Equilibrium: This section covers the principles of chemical equilibrium, including the concept of Le Chatelier's principle and the equilibrium constant.
Electrochemistry: This section covers the principles of electrochemistry, including the concept of half-cell reactions, galvanic cells, and electrolysis.
Chapters in Organic Chemistry:
Alkanes: This section covers the properties and reactions of alkanes, including their structure, isomerism, and combustion.
Alkenes: This section covers the properties and reactions of alkenes, including their structure, isomerism, and addition reactions.
Alkynes: This section covers the properties and reactions of alkynes, including their structure, isomerism, and addition reactions.
Aromatic compounds: This section covers the properties and reactions of aromatic compounds, including their structure, isomerism, and electrophilic substitution reactions.
In addition to the topics covered in the syllabus, the CBSE Class 12 Chemistry exam also tests students on their analytical and problem-solving skills, as well as their ability to apply the concepts learned in the classroom to real-world situations.
Students can also check out the Tips for the Class 12 Chemistry Exam. They can easily access the Class 12 study material in one place by visiting the CBSE Class 12 page at ANAND CLASSES (A School Of Competitions). Moreover, to get interactive lessons and study videos, download the ANAND CLASSES (A School Of Competitions) App.
Frequently Asked Questions on CBSE Class 12 Chemistry Syllabus
Q1
How many chapters are there in the CBSE Class 12 Chemistry as per the syllabus?
There are 10 chapters in the CBSE Class 12 Chemistry as per Syllabus. Students can learn all these chapters efficiently using the study materials provided at ANAND CLASSES (A School Of Competitions).
Q2
What is the marking scheme for CBSE Class 12 Chemistry practical exam according to the syllabus?
The marking scheme for CBSE Class 12 Chemistry practical exam, according to the syllabus, is 8 marks for volumetric analysis, 8 marks for salt analysis, 6 marks for the content-based experiment, 4 marks for the project and viva and 4 marks for class record and viva.
Q3
Which is the scoring chapter in Chemistry as per CBSE Class 12 syllabus?
The chapter Electrochemistry in Chemistry is the scoring chapter as per CBSE Class 12 syllabus.
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