Carbon Compounds Science Notes
Importent points :
- Organic and inorganic compounds are the two important types of compounds
- The constituent elements common in these compounds are carbon (C), hydrogen (H) and oxygen (O).
- The element carbon belongs to group 14 and its electronic configuration is 24. The valency of carbon is 4.
Bonds in carbon compounds :
→ Properties of carbon compounds :
- Carbon compounds have low melting and boiling points.
- These compounds are bad conductors of heat and electricity.
- The chemical bonds in carbon compounds do not produce ions.
- The force of attraction which holds the atoms together in a molecule is called a chemical bond.
- The number of chemical bonds that an atom of an element forms is called catenation power
- Ionic bonds and covalent bonds are the two important types of chemical bonds.
→ Bonds in carbon compounds :
|Carbon atom||Electronic configuration||Number of electrons in the Valence shell||Nearby noble gas and the electronic configuration|
|6C||2, 4||4||2||2, 8|
→ Carbon has 4 valence electrons and to attain the configuration of neon by sharing four valence electrons of other atoms. The shared electrons are accommodated in the overlapping region of valence shells of both the atoms.
→ As a result, both the atoms attain a noble gas configuration without generating any net charge on them, which means that atoms remain electrically neutral. Atoms attain stability due to these factors. Therefore this route is adopted by carbon atom to attain a noble gas configuration.
→ The chemical bond formed by sharing of two valence electrons between the two atoms is called covalent bond.
→ A covalent bond is clearly represented by drawing an electron-dot structure. In this method a circle is drawn around the atomic symbol and each of the valence electrons is indicated by a dot or a cross. The covalent bond formed between the atoms is indicated by showing the circles around the atomic symbols crossing each other.
→ The shared electrons are shown in the overlapping regions of the two circles by dot or cross. The electron-dot structure is also drawn without showing the circle. One covalent bond constitutes one pair of shared electrons. A covalent bond is also represented by a small line joining the symbols of the two atoms. The line structure is also called structural formula.
Carbon : A versatile element :
→ Carbon: A versatile element : In short, the entire living kingdom is made from carbon. Carbon is the basic ingredient of our body. Millions of molecules ranging from the small and simple methane molecule to the extremely big D.N.A. molecule are made from carbon. The molecular masses of carbon compounds range up to 1012.
|Carbon Compound||Molecular mass|
|Methane CH4 (The smallest|
|Cooking gas (C3H8 + C4H10)||44/58|
|Sodium dodecyl benzene|
|sulphate (a detergent)||347|
Carbon compounds and molecular masses
Characteristics of carbon :
→ Carbon has a unique ability to form strong covalent bonds with other carbon atoms; this results in formation of big molecules. This property of carbon is called catenation power.
→ One, two or three covalent bonds can bond together two carbon atoms. These bonds are called single covalent bond, double covalent bond and triple covalent bond respectively. Example : ethane (CH3 – CH3). ethene (CH2 = CH2) and ethyne (CH = CH) which contain two carbon atoms.
→ Carbon being tetravalent, one carbon atom can form bonds with four other atoms (carbon or any other). This results in formation of many compounds. These compound possess different properties as per the atoms to which carbon is bonded.
→ For example, five different compounds are formed using one carbon atom and two monovalent elements hydrogen and chlorine : CH4, CH3Cl, CH2Cl2, CHCl3, CCl4 Similarly carbon atoms form covalent bonds with atoms of elements like O, N, Shalogen and P to form different types of carbon compounds in large number
→ Isomerism is one more characteristic of carbon compound which is responsible for large number of carbon compounds.
Hydrocarbons, functional groups and homologous series :
→ Saturated hydrocarbon : In hydrocarbon, the four valencies of carbon atom are satisfied only by the single bonds, such compounds are called saturated hydrocarbons. e.g. Ethane (C2H6), Propane (C3H8).
→ Unsaturated hydrocarbon : The carbon compounds having a double bond or triple bond between two carbon atoms are called unsaturated hydrocarbons.
→ The unsaturated hydrocarbons containing a carbon-carbon double bond are called alkenes. e.g. Ethene (CH2 = CH2), Propene (CH3 – CH = CH2)
The unsaturated hydrocarbons containing a carbon-carbon triple bond are called alkynes. e.g. Ethyne (CH = CH)
→ In the course of millions of years the reserves of crude oil were formed from the dead organisms buried under the sea floor. This crude oil and natural gas are now recovered from the oil wells. The natural gas is mainly methane.
→ The crude oil is a complex mixture of thousands of different compounds. It mainly contains various hydrocarbons. Various useful components such as CNG, LPG, petrol (gasoline), rockel, diesel, engine oil, lubricant, etc. are obtained by separating crude oil using fractional distillation.
→ Structural Isomerism : Butane is represented by two different compounds, as their structural formulae are different. These two different structural formulae have the same molecular formula, i.e. C4 H10
→ The closed chain of carbon atoms are present in some carbon compounds, wherein, rings of carbon atoms form. For example, the molecular formula of cyclohexane is CH and its structural formula contains a ring of six carbon atoms.
→ Benzene is a cyclic unsaturated hydrocarbon. There are three alternate double bonds in the six membered ring structure of benzene. The compounds having this characteristic unit in their structure are called aromatic compounds.
→ Functional group : The compound acquire specific chemical properties due to these hetero atoms or the groups of atoms that contain hetero atoms, irrespective of the length and nature of the carbon chain in that compound. Therefore, these hetero atoms or the groups of atoms containing hetero atoms are called functional groups.
→ Homologous series : The length of the carbon chains in carbon compounds is different, their chemical properties are very much similar due to the presence of the same functional group in them. The series of compounds formed by joining the same functional group in place of a particular hydrogen atom on the chains having sequentially increasing length is called homologous series. Two adjacent members of the series differ by only one – CH2 – (methylene) unit and their mass differ by 14 units.
Characteristics of Homologous series :
→ In homologous series while going in an increasing order of the length of carbon chain
- one methylene unit ( – CH2 – ) gets added
- molecular mass increases by 14 u
- number of carbon atoms increases by one.
→ Chemical properties of members of a homologous series show similarity due to the presence of the same functional group in them.
→ Each member of the homologous series can be represented by the same general molecular formula
→ While going in an increasing order of the length there is gradation in the physical properties, i.e. the boiling and melting points.
Nomenclature of carbon compounds :
→ IUPAC nomeclature system : International Union for Pure and Applied Chemistry (IUPAC) put forth a nomenclature system based on the structure of the compounds, and it was accepted all over the world. There are three units in the IUPAC name of any carbon compound : parent, suffix and prefix.
→ IUPAC name :
CH3 – CH2 – OH
Parent name: Ethane
Suffix: -OH (ol)
Parent suffix: Ethanol
IUPAC name: Ethanol.
Parent name: Pentane
Suffix: – OH (ol)
Assign numbering : 2
Parent suffix: Pentan – 2 – ol
IUPAC name: Pentan – 2 – ol.
- Methane is the component of biogas that makes it useful as fuel.
- Carbon dioxide is formed by the combustion of elemental carbon.
- The biogas combustion is exothermic reaction.
Chemical properties of carbon compounds :
Properties of carbon compounds:
→ Combustion : Methane undergoes combustion in the presence of oxygen to emit heat and light to form carbon dioxide and water.
→ Oxidation : Ethanol gets oxidised in the presence of alkaline potassium permanganate to form ethanoic acid.
→ Addition reaction : Vegetable oil (unsaturated compound) undergoes addition reaction with hydrogen in the presence of nickel catalyst to form vanaspati ghee (saturated compound).
→ Substitution reaction : The reaction in which the place of one type of atom/group in a reactant is taken by another atom/group of atoms, is called substitution reaction. Chlorination of methane, is a substitution reaction which gives four products.
→ Ethanol : Ethanol is a colourless liquid at room temperature and its boiling point is 78 “C. Generally ethanol is called alcohol or spirit. Ethanol is soluble in water in all proportions. When aqueous solution of ethanol is tested with litmus paper it is found to be neutral.
→ Ethanol being good solvent, it is used in medicines such as tincture iodine (solution of iodine and ethanol), cough mixture and also in many tonics.
→ Methanol (CH,OH), the lower homologue of ethanol, is poisonous, and intake of its small quantity can affect vision and at times can be lethal. To prevent the misuse of the important commercial solvent ethanol, it is mixed with the poisonous methanol. Such ethanol is called denatured spirit. A blue dye is also added to it, so that it is easily recognised.
→ Chemical properties of ethanol : Reaction with sodium
→ All the alcohols react with sodium metal to liberate hydrogen gas and form sodium alkoxide salts. When ethanol reacts with sodium metal, hydrogen gas and sodium ethaoxide are formed.
→ Dehydration reaction: When ethanol is heated at the temperature 170 C with excess amount of concentrated sulphuric acid, to form ethene, with elimination of water molecule.
Here, concentrated sulphuric acid acts as a dehydrating agent.
→ Ethanoic acid : Ethanoic acid is a colourless liquid with boiling point 118 °C. Ethanoic acid is commonly known as acetic acid. Its aqueous solution is acidic and turns blue limus red. Vinegar, which is used as preservative in pickles, is a 5-8% aqueous solution of acetic acid. The melting point of pure ethanoic acid is 17 °C. Therefore during winter in cold countries ethanoic acid freezes at room temperature itself and looks like ice. Therefore it is named ‘glacial acetic acid’.
Chemical Properties of ethanoic Acid :
Reaction with base :
→ A reaction with strong base Ethanoic acid gives neutralization reaction with a strong base sodium hydroxide to form a. salt and water.
→ Ethanoic acid reacts with sodium carbonate to form sodium ethanoate, water and carbon dioxide.
→ Esterification reaction : Ethanoic acid reacts with ethanol in presence of an acid catalyst, ethyl ethanoate (ester) is formed. This reaction is known as esterification.
→ Esters have sweet odour. Esters are used for making fragrances and flavouring agents. Saponifaction: When an ester is reacted with the alkali sodium hydroxide, the corresponding alcohol and sodium salt of carboxyclic acid are obtained.
→ This reaction is called saponification reaction, as it is used for preparation of soap from fats. Ester + Sodium hydroxide → Sodium Carboxylate + Alcohol
→ When fat is heated with NaOH solution, soap and glycerin are obtained.
Macromolecules and polymers :
Macromolecules and polymers:
- Macromolecules : The giant carbon molecules formed from hundreds of thousands of atoms are called macromolecules.
- Natural macromolecules : Polysaccharides, proteins and nucleic acid and rubber, etc.
- Manmade macromolecules: Elastomers, plastic, nylon, etc.
- Polymers: A macromolecule formed by regular repetition of a small unit is called polymer. The small unit that repeats regularly to form a polymer is called monomer. The reaction by which monomer molecules are converted into a polymer is called polymerization.
→ Various polymers and their uses:
→ The polymer’s in the above examples are formed by repetition of single monomer. These are called homopolymers. The other type of polymers are formed from two or more monomers. They are called copolymers.
→ For example, PET is poly ethylene terephthalate. The structures of polymers are linear as in the above examples or they are branched and cross linked as well. Polymers aquire various properties as per the nature of the monomers and the type of structure.
→ Some natural polymers and their occurrence :