Carbon and Its CompoundsCARBON An element A non-metal Present in earths crust- 0.02% ( in form of minerals carbonates, coal, petroleum, etc.) and in atmosphere 0.03% ( CO2) Present in all living things ( Carbon compounds---- Organic Compounds) Always forms Covalent bonds. Is tetravalent Occurs in both free and combined state.COVALENT BONDSAt. no. is 6 ---- K-2 ; L-4 ----- To become stable it should either gain 4 electrons or lose 4 electrons. It cannot gain 4 electrons -It would be difficult for nucleus with 6 protons to hold 10 electrons. It cannot lose 4 electrons -It would require large amount of energy to remove 4 electrons .This problem is overcome by sharing its valence electrons with other atoms of carbon or with atoms of other elements. Covalent bonds are very strong and do not break easily because the carbon atoms are very small in size due to which their nuclei hold the shared pair of electrons between atoms strongly .CARBON IS TETRAVALENTTetra - 4 ;Valent valencySELF COMBINATION ( Catenation)Carbon atoms form long chains which are useful to us as we can derive large no. of carbon compounds. Carbon compounds are exceptionally stable as they form strong bonds among themselves and with other elements.OCCURRENCE OF CARBON In free state --- Diamond , Carbon, Buckminsterfullerene In combined state ---- In form of compounds CO2in air Carbonates ( limestone, marble, chalk) Fossil fuels ( coal , petroleum, natural gas) Organic compounds ( carbohydrates, fats and proteins) Wood, cotton wool, etc.ALLOTROPES OF CARBONThe various physical forms in which an element can exist.1. Diamond -----Colourless , transparent substance with extraordinary brilliance.Extremely hard , heavy, does not conduct electricity, burns on strong heating to give CO2, high melting point ( more than 3500C )Structure of DiamondEach carbon atom in the diamond crystal is linked to four other carbon atoms by strong
covalent bonds and forms a regular tetrahedron. Due to this the structure gets very rigid .Uses of Diamond Making rock borers for drilling oil wells Making glass cutters For jewellery making For removing cataract from eyes. Diamonds can also be made artificially by subjecting pure carbon to very high pressure and temperature . These are also called Synthetic diamonds.2. Graphite - It is a grayish black opaque substance , lighter than diamond, soft and slippery to touch, conducts electricity, burns on strong burning to give CO2 . The chemical properties of both diamond and graphite are same as both burn in oxygen to give carbon dioxide. However, their physical properties are different due to difference in their structures ( different arrangements of carbon atoms).Structure of GraphiteEach graphite crystal consists of layers of carbon atoms. Each carbon atom is joined to three other carbon atoms by strong covalent bonds to form flat hexagonal rings. Due to sheet like structure it is a soft substance due to which it is used as a dry lubricant for machine parts. It is a good conductor of electricity---Each carbon atom is joined to only three other carbon atoms by covalent bonds i.e. only 3 atoms are used in bond formation leaving the 4th atom to move freely. Due to this free electron , it conducts electricity.Uses of Graphite As lubricant for fast moving parts of machinery. For making carbon electrodes in dry cells and electric arcs. (The black coloured anode of a dry cell is made of graphite) For making pencil leads and black paints.Buckminsterfullerene -- C60It is an allotrope containing 60 carbon atoms joined together to form spherical molecules.It is a spherical molecule with atoms arranged in interlocking hexagonal and pentagonal rings . There are twenty hexagons and twelve pentagons of carbon atoms in one molecule.
It is a dark solid at room temp. , burns to give CO2, neither hard nor soft.ORGANIC COMPOUNDSThe compounds of carbon are known as organic compounds as they contain hydrogen and many organic compounds containing oxygen or other elements. So, most organic compounds are HYDROCARBONS or their derivatives. They are covalent compounds having low melting and boiling points. Oxides of carbon , carbonates, hydrogencarbonates and carbides are also carbon compounds but they are not considered as organic compounds because their properties are different from those of common organic compounds.Two properties of carbon 1. Catenation-atoms join with one another to form long chains .3 types of chains ---i) - Straight chainii) - Branched chainiii) - Closed chain2. Tetravalent Types of Organic compounds -1. Hydrocarbons2. Haloalkanes3. Alcohols4. Aldehydes5. Ketones6. Carboxylic acids ( Organic acids)HYDROCARBONSA compound made up of hydrogen and carbon only . Natural source is petroleum.Two types-- Saturated ; unsaturated1. Saturated Hydrocarbons (Alkanes)-Carbon atoms are connected with single covalent bonds and end with ane. They are unreactive.The general formula isCnH2n+21. Unsaturated Hydrocarbons ( Alkenes and Alkynes) -Carbon atoms are connected by a double bond or a triple bond .These are obtained mostly from petroleum by a process called cracking.1. Alkenes --- CnH2nAlkenes contain a double bond between two carbon atoms which is formed by sharing of two electron pairs. Simplest alkene is Ethene.1. Alkynes --- CnH2n-2Alkynes contain a triple bond between two carbon atoms which is formed by sharing of three electron pairs. Simplest Alkyne isEthyne whose common name isAcetylene.Alkyl Groups ---- CnH2n+1The group formed by the removal of one hydrogen atom from an alkane molecule .Methyl group (CH3-) is formed by the removal of one H atom from Methane (CH4) , etc.Cyclic HydrocarbonsHydrocarbons in which the carbon atoms are arranged in the form of a ring. They may be saturated or unsaturated.1. A saturated cyclic hydrocarbon is cyclohexane C6H12Electron dot structure is obtained by putting two electron dots in place of every single bond in its structural formula.Cyclopropane - C3H6Cyclobutane C4H8Cyclopentane - C5H10General formula of cycloalkanes is CnH2n1. An unsaturated cyclic hydrocarbon is benzene ( aromatic compounds ) whose electron dot structure is -- 2 electrons in place of every single bond and 4 electrons in place of every double bond in its structural formula.Single bond-- 2 shared electronsDouble bond -- 4 shared electronsNaming Hydrocarbons ---1 carbon atomMeth
2Eth
3Prop
4But
5Pent
6Hex
7Hept
8Oct
9Non
10Dec
Single Bondane
Double Bondene
Triple Bondyne
Isomers :-The organic compounds having the same molecular formula but different structures. Normal butanehas a straight line structure whereasiso-butanestructure has a branched chain structure. Isomerismis possible only with hydrocarbons having 4 or more carbon atoms ie. Isomerim is not possible in methane, ethane and propane. 1stisomeris calledn- pentane (normal) 2ndisomeris called isopentane 3rdisomeris called neopentaneHOMOLOGOUS SERIESA group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2group.Two adjacent homologous groups differ by 1 carbon atom and 2 hydrogen atoms .General formula of Alkanes ---CnH2n+2Characteristics of a Homologus Series1. All members represented by same general formula.2. Two adjacent homologues differ by a CH23. Difference between molecular masses of any 2 homologues is14.4. All compounds show similar chemical properties.5. There is gradual change in their physical properties with increase in molecular masses. ( melting , boiling points and densities increase)Alkenes ---- CnH2nAlkynes ---- CnH2n-2Functional GroupsAn atom or a group of atoms which makes a carbon compound reactive and decides its properties.1. Halo Group : X ( X can be Cl, Br or I)Chloro , Bromo and Iodo group ----
When 1 H atom of an alkane is replaced by a halogen atom, we get Haloalkane.Eg. CH4 Replace one H by Cl CH3ClGeneral formula isCnC2n+1X ( X may be Cl ; Br ;I )Chloromethane CH3Cl ---- methyl chlorideBromomethane -CH3Br ---- methyl bromideChloroethane -C2H5Cl ---- ethyl chlorideChloropropane -C3H7Cl ---- propyl chloride2. Alcohol Group : OH ( alcoholic / hydroxyl group)Alcohol group is made up of 1 oxygen and 1 hydrogen atom joined together.1 H atom is replaced by an alkane by a hydroxyl group ( OH group)CH4 Replace 1 H by OH CH3OHGeneral formula isCnH2n+1OHMethanol -CH3OH ---- methyl alcoholEthanol - C2H5OH ---- ethyl alcoholPropanol - C3H5OH ---- propyl alcohol3. Aldehyde Group :It consists of 1 carbon, 1 hydrogen and 1 oxygen atom joined together.General formula ---CnH2nOMethanal - HCHO --- formaldehydeEthanal - CH3CHO ---- acetaldehydePropanal CH3CH2CHO --- propionaldehydeButanal - CH3CH2CH2CHO4. Ketone Group :It consists of 1 carbon and 1 oxygen atom. A ketone group must contain at least 3 carbon atoms.General formula --CnH2nOPropanone - CH3COCH3---- acetone ( simplest ketone)Butanone - CH3COCH2CH3Pentanone - CH3COCH2CH2CH35. 6. Alkene Group :It is a Carbon carbon double bond.
Ethene - CH2= CH2Propene - CH3 CH = CH27. Alkyne Group :CCEthyne - CHCHPropyne - CH3CCHCOAL AND PETROLEUMWhen a fuel is burned , the energy is released mainly as heat which can be used for various purposes like cooking, heating , etc. Most of the fuels are either free carbon or carbon compounds. They are obtained from coal, petroleum and natural gas which are also calledFossil Fuelsbecause they were formed by the decomposition of the remains of the pre-historic plants and animals buried under the earth long ago.Formation of coal -It is formed by the decomposition of large land plants and trees buried under the earth millions of years ago. Due to high temp. and pressure inside the earth, and in absence of air, wood was converted into coal.Formation of petroleum -It was formed by the decomposition of the remains of extremely small plants and animals buried under the sea millions of years ago. It is a dark coloured, viscous and foul smelling crude oil which is a mixture of several solid, liquid and gaseous hydrocarbons mixed with water , salt an dearth particles. The fuels such as coal and petroleum have some nitrogen and sulphur in them . So, when they burn they lead to oxides of nitrogen and sulphur which are major pollutants of air.Burning of substances with or without flame ----A flameis a region where combustion of gaseous substances takes place. So, a flame is produced only when gaseous substances burn. All gaseous substances burn with a flame but only those solid and liquid fuels which vaporize on heating burn with a flame. Two types of flames - Blue ; Yellow Colour of flame depends upon the proportion of oxygen available for burning of fuel. Blue Flame -When the oxygen supply is sufficient . It does not produce muchlight Non-luminous.eg. gas stove. Yellow Flame - Oxygen supply insufficient . Yellow color is due to the glow of hot, unburnt carbon particles produced due to incomplete combustion of fuel .It produces light Luminous. Eg. candle Solid and liquid fuels which do not vaporise on heating , burn without producing a flame.eg. charcoal and coal.CHEMICAL PROPERTIES OF CARBON COMPOUNDS Combustion --Process of burning of a carbon compound in air to give CO2, water, heat and light.i. Alkanes burn in air to produce lot of heat due to which they are excellent fuels. Eg. methane , Butane (LPG). They burn in air with blue, non-sooty flame because the % of carbon in the saturated hydrocarbons is comparatively low which gets oxidized completely by the oxygen present in the air.ii. The stoves have tiny holes for air so that sufficient oxygen is available for complete burning of fuel to produce a smokeless blue flame.iii. Mixture of acetylene(ethyne) and air is not used for welding because burning of ethyne in air produces a sooty flame , which is not hot enough to melt metals for welding.Substitution reactions ---The reaction in which one or more hydrogen atoms of hydrocarbons are replaced by some other atoms like chlorine ( chlorination).iv. Saturated hydrocarbons ( alkanes) are unreactive because they contain only carbon-carbon single bonds. They do not react with many substances.v. They undergo substitution reactions with chlorine in the presence of sunlight.vi. Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.CH4+ Cl2 CH3Cl + HCl 1 H atom of methane is replaced by Cl atom and we get chloromethane .By supplying more chlorine , all H atoms can be replaced by Cl one by one.So, we can obtain 3 more compounds ---Dichloromethane / methylene dichloride --- CH2Cl2Trichloromethane / Chloroform ---- CHCl3vii. Addition Reactions -The unsaturated hydrocarbon combines with another substance to give a single product ( addition of H, Cl or Br)i. These reactions are given by all unsaturated hydrocarbons containing double or triple bonds ( alkenes and alkynes)ii. Simplest alkene is Ethene which reacts with hydrogen when heated in the presence of nickel catalyst to form ethane .iii. Unsaturated hydrocarbons add on hydrogen in the presence of catalysts such as Nickel or Palladium(Pd) to form saturated hydrocarbons which is called HYDROGENATION . This process is used to prepare vegetable Ghee form vegetable oils.ETHANOL / ETHYL ALCOHOL ( C2H5OH )Physical properties :- Colourless liquid having pleasant smell and burning taste . Volatile liquid having low boiling point . Lighter than water so it is soluble. Solubility of ethanol in water is due ot the presence of hydroxyl group in it. Does not contain any hydrogen ions neutral compound. No effect on litmus paper.Chemical properties :-1. Combustion :-It is highly inflammable liquid and catches fire easily and starts burning in air with a blue flame to form CO2and water vapour and releases lot of heat and light.C2H5OH + 3O2 2CO2+ 3H2O + heat + light Since it burns with a clear flame giving lot of heat, it is used as a fuel. Used as an additive in petrol. It does not produce any poisonous gas like carbon monoxide . Produced on large scale from sugarcane crop. ( after crystallization of sugar from concentrated sugar cane juice , a thick, dark brown liquid called molasses is left behind. Ethanol is produced by fermentation of the cane sugar present in molasses)2. Oxidation:-It means controlled combustion. When ethanol is heated with alkaline potassium permanganate solution , it gets oxidized toethanoic acid.CH3CH2OH + 2O CH3COOH + H2OEthanoic acid is formed by the oxidation of ethanol by using a strong oxidizing agent.i. Oxidation of ethanol to ethanoic acid can also be done by using acidified potassium dichromate as the oxidizing agent ( in place of alkaline potassium permanganate) .3. Reaction with sodium metal :-Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas :2C2H5OH + 2Na ? 2 C2H5ONa + H24. Dehydration :-It means removal of water molecule from it.When ethanol is heated with excess of conc. H2SO4( dehydrating agent)it gets dehydrated to form ethene.CH3- CHOH ?CH2= CH2+ H2O5. Reaction with Ethanoic acid :-Ethanol reacts with ethanoic acid on warming in the presence of a few drops of conc. H2SO4to form a sweet smelling ester , ethyl ethanoate .CH3COOH + C2H5OH ? CH3COOC2H5+ H2Oi. The reaction in which a carboxylic acid combines with an alcohol to form an ester is called esterification. It takes place in the presence of a catalyst H2SO4.USES OF ETHANOL1. Manufacture of paints, varnishes, medicines, perfumes, dyes, soaps and synthetic rubber.2. Used as a solvent.3. Used as a fuel.4. Used in alcoholic drinks5. Used as an antiseptic to sterilize wounds.ETHANOIC ACID ( ACETIC ACID - CH3COOH )A dilute solution of ethanoic acid in water is called vinegar .Physical properties :-1. Colourless liquid having a sour taste and a smell of vinegar.2. Boiling point is 118C3. On cooling , it freezes to form a colorless , ice-like solid ( like glacier) so it is also called glacial ethanoic / acetic acid.4. Miscible with water in all proportions.Chemical Properties :-1. Action on litmus-Turns blue litmus red ; universal indicator paper to orange ( 4 pH) showing it is a weak acid.2. Reaction with Carbonates and Hydrogencarbonates :-i. With Sodium Carbonate Forms sodium ethanoate ( sodium acetate ) and CO2gas.2CH3COOH + Na2CO3? 2 CH3COONa + CO2+ H2Oii. With Sodium Hydrogencarbonate -Forms sodium ethanoate and evolves brisk effervescence of CO2gas.CH3COOH + NaHCO3? CH3COONa + CO2+ H2O3. Reaction with Sodium Hydroxide -- It reacts with bases to form salt and water .CH3COOH + NaOH ? CH3COONa + H2O( sodium ethanoate)4. Reaction with Alcohols - Reacts in presence of a little of Con. H2SO4to form esters.CH3COOH + C2H5OH ? CH3COOC2H5+ H2OSweet smelling ester is formed. Esters are volatile liquids having sweet / pleasant / fruity smell . They are used to make artificial perfumes , flavours and essences .Esters can be hydrolysed back to the alcohol and carboxylic acid when heated with sodium hydroxide solution.SOAPS AND DETERGENTSDetergent Any substance which has cleansing action in water.Two types ---Soapy and Non soapy ( detergents)Soaps-- Sodium or potassium salt of a long chain carboxylic acid( fatty acid) which has cleansing properties in water.It has a large non-ionic hydrocarbon group and an ionic group , COONa.Eg.Sodium Stearate C17H35COONa Sodium Palmitate - C15H31COONa Soap is the salt of a strong base ( sodium hydroxide) and a weak acidSo a solution of soap in water is basic in nature.Manufacture of soapSoapis made from animal fat or vegetable oils which when heated with sodium hydroxide solution ( caustic soda solution) , split to form sodium salt of higher fatty acid ( soap) and glycerol.Saponification -The process of making soap by the hydrolysis of fats and oils with alkalis . Common salt is added in soap making- It is added to the mixture to make the soap come out of the solution. It precipitates out all the soap from the aqueous solution. The soap which is used for washing clothes or bathing works by making the oil and grease particles dissolve in water because the oil and grease are insoluble in water.Structure of a Soap Molecule A soap molecule is made up of 2 parts :a long hydrocarbon and a short ionic part . The hydrocarbon part of the soap molecule is soluble in oil or grease so it can attach to the oil and grease particles present on dirty clothes. The short ionic part of the soap molecule is soluble in water so it can attach to the water particles .Micelle -A spherical aggregate of soap molecules in the soap solution in water. Soap solution is a colloidal solution. A soap solution appears cloudy because the soap micelles are large enough to scatter light.Limitations of soaps Soap is not suitable for washing clothes with hard water ---1. Large amt. of soap is wasted in reacting with calcium and magnesium ions of hard water to from insoluble precipitate calledscum. So larger amount of soap is needed.2. The scum formed sticks to the clothes and interferes with the cleaning ability of the additional soap , making cleaning difficult. Hard water contains calcium and magnesium salts.Detergents :-It is the sodium salt of a long chain benzene sulphonic acid ( or the sodium salt of a long chain alkyl hydrogensulphate) which has cleansing properties in water.They are also called soap-less soaps because though they act like a soap in having the cleansing properties, they do not contain the usual soaps like sodium stearate , etc. Detergents are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water and can be used for washing even with hard water.Advantages of detergents 1. Can be used with hard water2. Have strong cleansing action than soap.3. More soluble in water than soaps.Disadvantage of detergents over soaps -Some detergents are biodegradable , they cannot be decomposed by micro organisms like bacteria and hence cause water pollution in lakes and rivers .All soaps are bio- degradable and do not cause pollution.Lewis Structures: Simple OrganicCompoundsC2H4is the symbol for the simple organic compound,ethylene. It is the simplestalkene(hydrocarbon withcarbon-carbon double bonds). This illustration demonstrates how to draw the Lewis dot structure forC2H4.
The first step is to write the symbols for carbon (C) adjacent to each other in the center and the hydrogens (H) will have to surround the carbons. The hydrogen atoms will be distributed evenly on the outside of the molecule so we draw 2 symbols forH outside each carbon. The next step is to draw the valence electrons. Hydrogen has 1 carbon has 4.
In this diagram, the dots were connected to show that thevalence electronsare beingsharedincovalent bonds. Each of the lines represent 2 electrons being shared. Remember that hydrogen needs 2 valence electrons (aduet) to complete its outer shell. Carbon needs 8 valence electrons (anoctet) to complete its outer shell. As we look over this diagram, we can see thatby sharing in covalent bonds, every atom has a full outer shell of valence electrons (2 around each hydrogen and 8 around each carbon).C2H2is the symbol for the simple organic compound,acetylene. It is the simplestalkyne(hydrocarbon withcarbon-carbon triple bonds). This illustration demonstrates how to draw the Lewis dot structure forC2H2.
To begin, a C for each central carbon was drawn in the center. The hydrogens must go on the outside and they must be as far apart from each other as possible, so we draw one on each side of the molecule in line with the carbon atoms. Next we put in a dot for each electron and connect the dots.CH2Ois the symbol for the simple organic compound,formaldehyde. It is the simplestaldehyde(hydrocarbon with a carbon atom connected to an oxygen atom by adouble bondand to a hydrogen atom by asingle bond). This illustration demonstrates how to draw the Lewis dot structure for CH2O.
On the left the attempt to draw the Lewis structure failed when we attempted to join one of the hydrogens to oxygen. However, on the right, we know it is the correct Lewis structure because all atoms have their complete set of valence electrons. There are 8 surrounding oxygen and carbon (a completeoctet) and hydrogen has its full set of 2 (duet).Solutions to problems:
Lewis CHCl3CHCl3= Chloroform, also known as trichloromethane and methyl trichloride
Lewis HCNLewis Hydrogen Cyanide
Lewis H2O2Lewis Hydrogen Peroxide
Lewis H2CO2 or HCO2HLewis Formic Acid
