CH 4 Carbon and its Compounds PDF

CH: 4 CARBON AND ITS COMPOUNDS Covalent Bond: Neutral carbon atom has electronic configuration 2, 4. To gain inert gas configuration, carbon can either donate 4 valence electrons or gain 4 electrons, but it cannot do so for the following reasons: 1. Carbon is a small atom and its valence electrons...

CH: 4 CARBON AND ITS COMPOUNDS Covalent Bond: Neutral carbon atom has electronic configuration 2, 4. To gain inert gas configuration, carbon can either donate 4 valence electrons or gain 4 electrons, but it cannot do so for the following reasons: 1. Carbon is a small atom and its valence electrons are strongly attracted by its nucleus. Therefore, it cannot lose 4 electrons (forming C4+ cation) as it requires large amount of energy to remove four electrons. 2. Carbon cannot gain 4 electrons, because addition of 4 electrons in valence shell (forming C 4- anion) will result in strong electronic repulsion between 8 electrons now present in valence shell and the energy required to overcome these repulsion is very high. Thus, carbon overcomes this problem by sharing of its valence electrons with other carbon atoms or with atoms of other elements. The bond formed by mutual sharing of electron pairs between two atoms in a molecule is known as Covalent Bond. The bond formed by equal contribution and mutual sharing of electrons between two atoms (same or different) so that both the atoms acquire the stable nearest noble gas configuration is called covalent bond Types of Covalent Bond:  Single Covalent Bond: When a single pair of electrons are shared between two atoms in a molecule. For example; F2, Cl2, H2 etc.  Double Covalent Bond: When two pairs of electrons are shared between two atoms in a molecule. For example; O 2, CO 2 etc.  Triple Covalent Bond: When three pairs of electrons are shared between two atoms in a molecule. For example; N 2 etc. Electron Dot Structure: The electron dot structures provides a picture of bonding in molecules in terms of the shared pairs of electrons and octet rule. Formation of Hydrogen Molecule Atomic number of Hydrogen = 1 Number of valence electrons = 1 Formation of CO2 Molecule Atomic number of Carbon = 6 [2, 4] Number of valence electrons = 4 Atomic number of Oxygen = 8 [2, 6] Number of valence electrons = 6 Formation of N2 Molecule Atomic number of Nitogen = 7 [2, 5] Number of valence electrons = 5 Properties of Covalent Compounds 1. Physical State: Covalent compounds exist as single molecules which are mostly in gaseous state eg, H2 , CH4 etc. However, some of them will be liquids and few may exists as solids 2. Melting and boiling points: since no ions are present in the covalent molecules, the attractive force them are them weak. Therefore, these compounds have usually low melting and boiling point. 3. Electrical conductivity: The covalent compounds are generally poor conductors of electricity because the current is carried by the movement of ions. 4. Solubility: The covalent compounds are normally not soluble in water. They dissolve in cova;ent solvents. Most of the organic compounds have low boiling and melting point, due to the weak force of attraction (i.e., the inter-molecular force of attraction) between these molecules. Most carbon compounds are poor conductors of electricity, due to the absence of free electrons and free ions. Allotropes of Carbon Allotropy: The phenomenon in which the element exists in two or more different physical states with similar chemical properties are called Allotropy. Carbon has Three Main Allotropes   Diamond: In this, carbon, an atom is bonded to four other atoms of carbon forming three- dimensional structures. It is the hardest substance and an insulator. It is used for drilling rocks and cutting. It is also used for making jewellery.  Graphite: In this, each carbon atom is bonded to three other carbon atoms by single covalent bonds. Graphite has sheet like structure having hexagonal layers. It has two dimensional structure. It is a good conductor of electricity and used as a lubricant.  Buckminster Fullerene: It is an allotrope of the carbon-containing cluster of 60 carbon atoms joined together to form spherical molecules. It is dark solid at room temperature. Versatile Nature of Carbon The existence of such a large number- of organic compounds is due to the following nature of carbon,  Catenation  Tetravalent nature. (i) Catenation: The self- linking property of an element mainly carbon atom through covalent bonds to form long straight, branched and rings of different sizes are called Catenation. This property is due to  Carbon cannot donate or gain four electrons required to gain inert gas configuration and therefore shows tendency to form covalent bonds.  Due to its small size, shared electron pair are strongly held by both nuclei which results in formation of strong covalent bonds. In practice it has been found that covalent bonds formed by carbon are exceptionally stable.  The Tetra-valency of carbon also helps in catenation. Carbon can also form stable multiple bonds (double or triple) with itself and with the atoms of other elements. (ii) Tetravalent Nature: Carbon has valency of four. It is capable of bonding with four other atoms of carbon or some other heteroatoms with single covalent bond as well as double or triple bond. Hydrocarbons Compounds of carbon and hydrogen are known as hydrocarbons. For example; Methane (CH4), Ethane (C 2H6), Ethene (C 2H4), Ethyne (C2H2) etc. Saturated Hydrocarbon Alkanes: General formula: CnH2n+2. Suffix: ane n = number of carbon atoms. In this, the carbon atoms are connected by only a single bond. For example; Methane (CH4), Ethane (C 2H6) etc. Unsaturated Hydrocarbons These are hydrocarbons which contain carbon to carbon double bonds or carbon to carbon triple bonds in their molecules. These are further classified into two types: alkenes and alkynes. Alkenes: General formula: CnH2n, Suffix : ene The hydrocarbons containing at least one carbon to carbon double bond are called alkenes. These were previously called olefins (Greek : olefiant – oil forming) because the lower gaseous members of the family form oily products when treated with chlorine. In higher alkenes, the position of the double bond, can be indicated by assigning numbers 1, 2, 3, 4, ……to the carbon atoms present in the molecule. Alkynes: General formula is CnH2n-2, Suffix : yne In this, the two carbon atoms are connected by triple bond. In higher members, the position of triple bond is indicated by giving numbers 1, 2, 3, 4, ….to the carbon atom in the molecule. Isomerism in Organic compounds Carbon compounds or organic compounds with same molecular formula can show different structures and hence, different properties. This phenomenon is called isomerism and compounds are called isomers. Structural Isomerism: Compounds having the same molecular formula but different structures are called Structural isomers. Examples: Isomers of Butane (C4 H10 ) and pentane (C5H12). Aromatic compounds Aromatic compounds are cyclic compounds. Benzene and its derivatives (which contain benzene ring or six membered cyclic ring having alternate single and double bonds) are called aromatic compounds. General formula of cycloalkane = CnH2n In cyclopentane n = 5, Formula of cyclopentane, C 5 H5 × 2 = C5 H10 Homologous Series: Series of organic compounds having the same functional group and chemical properties and successive members differ by a CH2 unit or 14 mass units are known as Homologous series. Homologous series of Alkanes, Alkenes and Alkynes Characteristic of Homologous Series  The successive members in homologous series differ by CH2 unit or 14 (CH2=12+2x1=14) mass unit.  All members of a series can be represented by the same general formula.  Members of given homologous series have the same functional group.  All the members of homologous series shows similar chemical properties.   The physical properties such as melting point, boiling point etc. of the members of a homologous series show almost regular variation in ascending or descending the series. Functional Group:  In hydrocarbon chain, one or more hydrogen atom is replaced by other atoms in accordance with their valancies. These are heteroatom.  These heteroatom or group of atoms which make carbon compound reactive and decides its properties are called functional groups.  The chemical properties of organic compounds are determined by the functional groups while their physical properties are determined by the remaining part of the molecule. Nomenclature of Carbon Compounds (i) Identify the root word Root word denotes the number of carbon atoms in the longest possible chain. eg:Meth( for one C), Eth ( for two C ) etc. ii) Suffix a) Primary suffix The suffix used to represent the saturation or unsaturation i.e., single, double or triple bond between carbon atoms present in the parent chain is called a primary suffix. eg: ane- for C-C bond, ene: for C=C bond, yne: for C ≡ C bond  b) Secondary suffix: The secondary suffix used to represent the nature of principal functional group present in the organic compound and it attached to primary suffix while writing the IUPAC name. The secondary infill of some common functional group are given in table. Class of organic compound Functional group Secondary suffix Alcohol -OH -ol Aldehyde -CHO -al Ketone >C=O -one Carboxylic acid -COOH -oic acid Ester -COOR -oate iii) Prefix The alkyl group and halogens are regarded as substituents or side chains. Their presence is indicated by writing suitable prefixes before the word root. eg Rules 1. Select the longest continuous chain of carbon atoms ( parent chain). it must include the atoms involved in the double bond, triple bond if present.( functional group also, if present) 2. The carbon atoms of the parent chain are numbered starting from one end in such way that the Carbon atoms involved in the multiple bond get the least possible number. for eg: ( Pent-2-ene or 2-Pentene). 3. When an alkene and an alkyne are present in the same molecule, the ending will always be “yne”. 4. Presence of a functional group is indicated by prefix or suffix. 5. If the name of the functional group is to be given as a suffix, the last letter ‘e’ in the name of the compound is deleted and the suffix is added. e.g., a ketone with three carbon atoms is named as : Propane – e = Propan + ‘one’ = Propanone. Alcohol with three carbons is propanol. Carboxylic acid with three carbons is propanoic acid. A carbon bonded to a functional group must have the lowest possible carbon number. Halogens, in IUPAC, are written as Prefixes, e.g., Compound With two carbons and one chloro group is named as chloroethane (CH3 CH2 CI). Chemical Properties of Carbon Compounds (a) Combustion- (all saturated and as unsaturated)  The process of burning of carbon or its compounds in presence of oxygen is called combustion. In combustion process, mainly two products are formed i) CO 2 and H2 O ii) Energy in the form of heat and light  Carbon and its compounds are used as fuels because they burn in air releasing lot of heat energy.(once carbon and its compounds ignite, they keep on burning without the requirement of additional energy. That’s why these compounds are used as fuels.)  Saturated hydrocarbon generally burn in air with blue and non-sooty flame. This is because the percentage of carbon in the saturated hydrocarbons is comparatively low which gets oxidized completely by the oxygen present in the air.  Unsaturated hydrocarbon burns in air with yellow sooty flame because percentage of carbon is higher than saturated hydrocarbon which does not get completely oxidized in air.  The gas and kerosene stove used at home has inlet for air so that, burnt to given clean blue flame.  Due to presence of small amount of nitrogen and sulphur, coal and petroleum produces carbon dioxide with oxides of nitrogen and sulphur which are major pollutant. (b) Oxidation- (all saturated and as unsaturated) Addition of oxygen to any substance is called oxidation and the substances which are capable of adding oxygen to other substances are called oxidizing agents. Alcohols can be converted to carboxylic acid in presence of oxidizing agent alkaline KMnO4 (potassium permangnate) or acidic potassium dichromate. (c) Addition Reaction- (Only unsaturated hydrocarbons) Addition reaction are the characteristic property of unsaturated hydrocarbons. Addition reaction are those reactions in which atom or groups of atoms are simply added to a double bond or triple bond without the elimination of any atom or other molecules. The addition of hydrogen molecule to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation. Unsaturated hydrocarbon add hydrogen in the presence of catalyst palladium or nickel. Vegetable oils are converted into vegetable ghee (Vanaspati ghee) using this process. It is also called hydrogenation of vegetable oils. d) Substitution Reaction-(Only saturated hydrocarbons) Replacement of one or more hydrogen atom of an organic molecule by another atom or group of the atom is known as Substitution Reaction. Due to the presence of strong C-C single bonds and C-H single bond, saturated hydrocarbons are quite unreactive and are inert to the action of most of the reagents. It is because this reason alkanes are also called paraffins. However, in the presence of sunlight or heat, chlorine reacts very rapidly with alkanes to from substitution products. Important Carbon Compounds: a) Ethanol( Ethyl Alcohol , C2H5OH) Physical Properties of Ethanol Colourless liquid at room temperature, pleasant smell and burning taste. Soluble in water. Volatile liquid with low boiling point of 351 K. Neutral compound. Chemical Properties i) Reaction with Sodium Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas: This reaction is used as a test for ethanol by evolution of H2 gas (Burn with pop sound). ii) Dehydration Dehydration means removal of water molecule from a compound. Ethanol on heating with excess of conc. sulphuric acid at 170o C, releases water molecule to form ethane (unsaturated hydrocarbon) In this reaction Conc. H2 SO4 acts as dehydrating agent. USES OF ETHANOL  As an anti-freeze in automobile radiators.  As a preservative for biological specimen.  As an antiseptic to sterilize wounds in hospitals.  As a solvent for drugs, oils, fats, perfumes, dyes, etc.  In the preparation of methylated spirit (mixture of 95% of ethanol and 5% of methanol), rectified spirit (mixture of 95.5% of ethanol and 4.5% of water), power alcohol (mixture of petrol and ethanol) and denatured sprit (ethanol mixed with pyridine).  In cough and digestive syrups. [EVIL EFFECTS OF CONSUMING ALCOHOL If ethanol is consumed, it tends to slow down metabolism of our body and depresses the central nervous system. It causes mental depression and emotional disorder. It affects our health by causing ulcer, high blood pressure, cancer, brain and liver damage. Nearly 40% accidents are due to drunken drive. Unlike ethanol, intake of methanol in very small quantities can cause death. Methanol is oxidized to methanal (formaldehyde) in the liver and methanal reacts rapidly with the components of cells. Methanal causes the protoplasm to get coagulated, in the same way an egg is coagulated by cooking. Methanol also affects the optic nerve, causing blindness.] b) Ethanoic acid (Acetic Acid, CH3COOH) Physical Properties Colourless liquid having sour taste and have smell of vinegar. Boiling point is 391 K. When pure CH3 COOH is freezed, it forms colourless ice like solid. So it is called glacial acetic acid. Chemical Properties (i) Esterification (Reaction with alcohol) Ethanoic acid reacts with alcohols in the presence of a little of concentrated sulphuric acid to for, esters. For example, when ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, a sweet smelling component called ethyl ethanoate is formed:   Esters are usually volatile liquids having sweet smell or pleasant smell.  They are also said to have fruity smell.  Esters are used in making artificial perfumes (artificial scents).  Esters are also used as flavouring agents. The reaction of esters with alkalis, eg, NaOH gives carboxylic acid salt and alcohol which is used in the making of soaps by the process called saponification reaction. It is the reverse of esterification. ii) Reaction with Base Ethanoic acid reacts with bases (or alkalis) to form salts and water. For example, ethanoic acid reacts with sodium hydroxide to form a salt called sodium ethanoate and water: iii) Reaction with Carbonates and hydrogen carbonates Acetic acid reacts with carbonates and bicarbonates to evolve CO 2 gas with the formation of salt of acetic acid and water. Soaps and Detergents Soaps Soap is sodium or potassium salt of long chain carboxylic acid. E.g.,C17 H35 COO-Na+ Soaps are effective only in soft water. Soap molecule has : (i) Ionic (hydrophyllic) part: This part is hydrophilic (water-attracting) and is soluble in water but insoluble in oil. It typically carries a negative charge (anion), such as COO-Na+ (sodium salt of the carboxyl group). (ii) Long hydrocarbon chain (hydrophobic) part: This part is hydrophobic (water-repelling) and is insoluble in water but soluble in oil and grease.  Cleansing Action of Soap Most dirt is oily in nature and hydrophobic end attaches itself with dirt and the ionic end is surrounded with molecule of water. This result in formation of a radial structure called micelles. Soap micelles helps to dissolve dirt and grease in water and cloth gets cleaned. The magnesium and calcium salt present in hard water react with soap molecule to form insoluble product called scum. This scum create difficulty in cleansing action. By use of detergent, insoluble scum is not formed with hard water and cloths get cleaned effectively. Detergent  Detergents are ammonium or sulphonate salt of long chain of carboxylic acid. Example: CH3—(CH2)11—C6H4—SO3Na.  Detergents are effective in both hard and soft water.  Water that does not produce lather with soap readily is called hard water and which produces lather with soap is called soft water.  Hardness of water is due to the presence of bicarbonate s, chlorides and sulphate salt of calcium and magnesium.  Assignment (to be done in the register) 1. State reasons i) why covalent compounds a) are bad conductors of electricity b) have low melting and boiling points. ii) carbon exhibits catenation property much more than silicon. 2. Draw the electron dot structures for i) F2 ii)CH3Cl iii)CCl4 iv) C3H8 3. Write all the possible structural isomers of the molecular formula C 6 H14. 4. Consider the molecular models of the two organic compounds shown below: a) Name the homologous series that compounds I and II belong to and give its general formula. b) Write the molecular formulae of next homologue of both compounds I and II. 5. Draw the electron dot structures and write the structural formula for the following compounds. a) 2-butyne b) pent-3-ene 6. Two compounds X and Y have the same molecular formula, C6H12. Compound X is saturated while compound Y is unsaturated. Draw their structures. 7. An organic compound A having molecular fomula C2H4O2 reacts with Sodium metal Na evolves a gas B which readily catches fire. A also reacts with Ethanol in the presence of concentrated Sulphuric acid to form a sweet smelling substance C in making perfumes. a) Identify the compounds A, B and C. b) Write balanced chemical equation to represent the conversion of (i).Compound A to compound B. (ii).Compound A to compound C. 8. Give the name of the following : a) An Aldehyde derived from Ethane. b) Ketone derived from Butane. c) The compound obtained by the Oxidation of Ethanol by Chromic anhydride. 9. Two carbon compounds A and B have the molecular formula C3H8 and C3H6 respectively. Which one of the two each most likely to show addition reaction? Justify your answer. Explain with the help of a chemical equation, how an addition is useful in vegetable Ghee industry. 10. Write down the difference between soap and detergents. 11. An organic compound A is widely used as a preservative in pickles and has a molecular formula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound B. i) Identify the compound A. ii) Write the chemical equation for its reaction with Ethanol to form compound B. iii) How can we get compound A back from B? iv) Name the process and write corresponding chemical equation. v) Which gas is produced when compound A reacts with washing soda? Write the chemical equation 12. An organic compound X with a molecular formula C2H6O undergoes oxidation with in presence of alkaline KMnO4 to form a compound Y. X on heating in presence of Conc. H2SO4 at 443K gives Z. which on reaction with H2O in presence of H2SO4 gives back `X.``Z` reacts with Br2 (aq) and decolorizes it. Identify X, Y, & Z and write the reactions involved. 13. Hydrocarbon `X` and `Y` having molecular formulae C3H8 and C3H6 respectively. Both are burnt in different spatula on the bunsen flame. Indicate the color of the flame produced by `X` and `Y`. Identify `X` and `Y`. Write the structural formulae. 14. A cyclic compound `X` has molecular formula C6H6. It is unsaturated and burns with sooty flame. Identify `X` and write its structural formula. Will it decolorize bromine water or not and why? 15. Two compounds `X` and `Y` have the same formula C2H4O2. One of them reacts with sodium metal to liberate H2 and CO2 with NaHCO3. Second one does not reacts with Na metal and NaHCO3 but undergo hydrolysis with NaOH to form salt of carboxylic acid and compound `Z` which is called wood spirit. Identify `X`, `Y`, and `Z` and write chemical equation for the reaction involved. 16. How would you bring about the following conversions? Name the process and write the reaction involved. (a)ethanol to ethene. (b)propanol to propanoic acid. 17. Write the structural formulae of all the isomers of hexane.