- Compounds are of two types:
(i) Organic Compounds
(ii) Inorganic Compounds - Organic Compounds are made up of Carbons and form the basis of all living organisms.
THE COVALENT BOND
- Carbon always forms a covalent bond.
- The bond formed by sharing of an electron pair between two atoms are known as covalent atoms.
- Noble gas configuration of Carbon: (i)Carbon is tetravalent; it does not form an ionic bond by either losing four electrons (C4+) or by gaining four electrons (C4-). It is difficult to hold four extra electrons and would require a large amount of energy to remove four electrons. So, carbon can form bonds by sharing its electrons with the electrons of other carbon atoms or with other elements and attain a noble gas configuration. (ii)The atoms of other elements like hydrogen, oxygen and nitrogen, chlorine also form bonds by the sharing of electrons.
- H – H single bond between hydrogen atoms (H2)
- O = O double bond between oxygen atoms (O2)
- N ≡ N triple bond between nitrogen atoms
- Water molecules have a single covalent bond between one oxygen and two hydrogen atoms.
PHYSICAL PROPERTIES OF COVALENT COMPUNDS
- Covalent compounds have low melting and boiling points as they have weak intermolecular force.
- They are generally poor conductor of electricity as electrons are shared between atoms and no charged particles are formed
VERSATILE NATURE OF CARBON
- The two characteristic properties of carbon element which lead to the formation of a large number of compounds :
- Catenation: Carbon can link with carbon atoms by means of covalent bonds to form long chains, branched chains and closed rings. Compound Carbon atoms may be linked by single, double or triple bonds.
- Tetravalency: Carbon has 4 valence electrons. Carbon can bond with four carbon atoms, monovalent atoms, oxygen, nitrogen and sulphur.
HYDROCARBON
- Compounds made up of hydrogen and carbon are
called hydrocarbons. - There are two types of Hydrocarbons.
(i) Saturated Hydrocarbons
(ii) Unsaturated Hydrocarbons
(i) Saturated Hydrocarbons
- Single bond between carbon atoms.
- ᅳCᅳCᅳ
- Alkanes are saturated hydrocarbons.
- General Formula: CnH2n+2
(ii) Unsaturated Hydrocarbons
- Double or triple bond between carbon atoms.
- Alkenes and Alkynes are unsaturated hydrocarbons.
- Alkenes: ᅳC=Cᅳ
General formula: CnH2n - Alkynes: ᅳC≡Cᅳ
General Formula: CnH2n-2
ELECTRON DOT STRUCTURE OF SATURATED HYDROCARBONS
- Ethane C2H6
- Names, molecular formulae and structure formulae of saturated hydrocarbons (Alkanes):
ELECTRON DOT STRUCTURE OF UNSATURATED HYDROCARBONS
- Ethene (C2H4)
- Ethyne (C2H2)
- Names, molecular formulae and structure formulae of unsaturated hydrocarbons (Alkenes and Alkynes):
CARBON COMPOUNDS ON THE BASIS OF STRUCTURE
(i)Straight(unbranched) Chain:
Example: C3H8
ᅳCᅳCᅳCᅳCᅳCᅳ
(ii)Branched:
These three above compounds have the same molecular formula but different structures are called structural isomers and the phenomenon is structural isomerism.
(iii)Cyclic:
Example: C6H12
FUNCTIONAL GROUPS
- In a hydrocarbon chain, one or more hydrogen atom is
replaced by other atoms in accordance with their valencies. These are heteroatoms. - These heteroatoms or group of atoms which make carbon compound reactive and decides its properties are called functional groups.
HOMOLOGOUS SERIES
- It is a series of compounds in which some functional group substitutes for the hydrogen in a carbon chain.
- Example: Alcohols – CH3OH, C2H5OH, C3H7OH, C4H9OH
- They have the same general formula.
- Any two homologues differ by – CH2 group and the difference in molecular mass is 14μ.
- They have the same chemical properties but show gradual change in physical properties.
- Nomenclature of Carbon Compounds
(i) Identify the number of carbon atoms in compounds.
(ii) Functional groups are indicated by suffix or prefix.
CHEMICAL PROPERTIES OF CARBON COMPOUNDS
(i)Combustion
- Carbon and its compounds are used as fuels because they burn in air releasing a lot of heat energy.
- Saturated hydrocarbons generally burn in air with a blue and non-sooty flame.
- Unsaturated hydrocarbon burns in air with a yellow sooty flame because the percentage of carbon is higher than saturated hydrocarbon which does not get completely oxidized in air.
(ii)Oxidation
Alcohols can be converted to carboxylic acid in the presence of oxidizing agent alkaline KMnO4 (potassium permanganate) or acidic potassium dichromate.
(iii)Addition Reaction
Unsaturated hydrocarbons add hydrogen in the presence of catalyst palladium or nickel. Vegetable oils are converted into
vegetable ghee using this process.It is also called hydrogenation of
vegetable oils.
(iv)Substitution Reaction
Important Carbon Compounds: Ethanol and Ethanoic acid
Physical Properties of Ethanol
- Colourless, pleasant smell and burning taste.
- Soluble in water.
- Volatile liquid with a low boiling point of 351 K.
- Neutral compound.
Chemical Properties of Ethanol
(i) Reaction with Sodium
2Na + CH3CH2OH → 2CH3CH2ONa+ + H2 (Sodium ethoxide)
This reaction is used as a test for ethanol by evolution of H2 gas (Burn with pop sound).
(ii) Dehydration
Physical Properties of Ethanoic Acid
- Colorless liquid has a sour taste and smells like vinegar.
- Boiling point is 391 K.
- When pure CH3COOH is freezed, it forms colorless ice like solid. So it is called glacial acetic acid.
Chemical Properties of Ethanoic Acid
(i) Esterification -Sweet smelling ester is formed. This is saponification as soap is prepared by this.
(ii) Reaction with base: NaOH + CH3COOH → CH3COONa + H2O
(iii) Reaction with carbonates and hydrogen carbonates :
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2 CHH2
COOH + NaHCOH2 → CH3COONa + H2O + CO2
SOAPS AND DETERGENTS
- Soap is sodium or potassium salt of long chain carboxylic acid. Example: C17H35COONa+
- Soaps are effective only in soft water.
Detergents are ammonium or sulphonate salt of long chain of carboxylic acid. - Detergents are effective in both hard and soft water.
- Soap molecule has:
(i) Ionic (hydrophilic) part
(ii) Long hydrocarbon chain (hydrophobic) part
Cleansing Action of Soap
- Most dirt is oily in nature and the hydrophobic end attaches itself with dirt and the ionic end is surrounded with molecules of water.
- This results in formation of a radial structure called micelles.
- Soap micelles help to dissolve dirt and grease in water and cloth gets cleaned.
- Soap is a mixture of micelles and helps to dissolve dirt and grease in water and cloth.
- The magnesium and calcium salt present in hard water react with the soap molecule to form an insoluble product called scum. This scum creates difficulty in cleansing action.
- By use of detergent, insoluble scum is not formed with hard water and clothes get cleaned effectively.