Before we read carbon and its compounds. There are two types of compounds:
- Organic compounds: Any compounds that contain carbon are organic compounds.
- Inorganic compounds: Compounds which don’t contain carbon are inorganic compounds.
Earlier we read ionic bonds and its properties. Further, in this section, we will study covalent bond and its property.
- The chemical bond formed between two or more atoms by sharing of electron pairs, than that bond is a covalent bond.
- The bond formed by carbon is always a covalent bond.
- Electron pairs between the atoms are called bonding pairs.
The noble gas configuration of carbon:
- Carbon has atomic number 6. Thus is tetravalent can complete its octet either by gaining 4 electrons or by losing 4 electrons. But it is difficult for carbon to lose 4 electrons or gain 4 electrons simultaneously, as it requires much energy for the same.
- Carbon prefers to share its electrons to form covalent bond. Thus attains noble gas configuration.
- Many atoms such as hydrogen, nitrogen, oxygen, chlorine etc. also forms covalent bond to attain noble gas configuration.
Properties of Covalent bonds:
- Within the molecule of covalently bonded molecules have strong bonds, but inter-molecular forces are small.
- There are low melting and boiling points of covalently bonded molecules.
- Covalent compounds are generally poor conductors of electricity.
Versatile nature of carbon:
The numbers of carbon compounds were recently estimated to be about three million! whose formulae are known to chemists. The property which led carbon to the formation of a large number of compounds are:
The unique property possessed by carbon is that it can form bond with other atoms of carbon. By this property, it forms large molecules. This property is known as catenation.
- By this property, carbon forms a long chain, branched chain, also arranged in rings.
- Carbon atoms can form a single, double or triple bond with other atoms.
- Saturated compounds: Compounds of carbon, which possess only single bonds between the carbon atoms.
- The extent of catenation in carbon atom is highest. No other atoms have such extent of catenation.
- Silicon is the other element which forms compounds with hydrogen which have chains of up to seven or eight atoms, but these compounds are very reactive.
- In case of the carbon-carbon bond, it is very strong and hence much stable. Thus, a large number of compounds are formed with many carbon atoms linked to each other.
The other exceptional property of carbon is it has a valency of 4. By this property, it can form 4 bonds. The other element which it forms a bond may be the carbon atom, a monovalent atom, oxygen, nitrogen sulphur and many more.
- Organic compounds entirely formed by carbons and hydrogen atoms are said to be a hydrocarbon.
- Hydrocarbons are the main source of combustible fuel.
There are two types of hydrocarbons:
When there is a single bond between the carbon atoms it is saturated hydrocarbons.
- Denoted by – C – C –
- Alkanes are saturated hydrocarbons.
- It contains single bond throughout the compound.
- General formula is CnH2n+2
- In saturated hydrocarbons, all the single bonds are satisfied thus forms a stable compound.
- Examples are Methane (CH4), Ethane (C2H6), Propane (C3H8) etc.
When there is a double or triple bond between carbon atoms than it comes in the category of unsaturated hydrocarbons.
- Alkenes are unsaturated hydrocarbons.
- Denoted by – C = C –
- It contains one or more double bond in the compound.
- General formula is CnH2n
- Alkynes are also unsaturated hydrocarbons.
- Denoted by – C ≡ C –
- It contains one or more triple bond in the compound.
- General Formula is CnH2n-2
Types of chains formed by carbon and its compounds:
1. Straight chain i.e. unbranched chain:
In this type of chain 1st and last carbon of the chain makes a bond with 3 hydrogen atoms and the rest with two carbon atoms and two hydrogen atoms.
2. Branched Chain:
In this type of chain, Tetravalency of carbon is satisfied by different types of arrangement of carbon and hydrogen atoms.
Structural Isomers: Those compounds which have the same molecular formula but different structures are called structural isomers.
3. Cyclic chain or rings:
In this type of chain carbon atoms are arranged in such a way that it forms a closed ring.
- When one or more hydrogen atom is in an organic compound (Carbon chain) is replaced by other atoms satisfying its valency than these atoms are called heteroatoms.
- These heteroatoms provide the compound with some specific property in terms of reactivity, so these heteroatoms are called functional groups.
- Halogens, Nitrogen, Oxygen and Sulphur are the primary functional groups.
- These functional groups decide the property of the compounds which it is attached.
List of functional groups and their structures:
|Cl/Br||Halo- (Chloro/bromo)||-Cl, – Br|
|4. Carboxylic acid|
- Homologous series is a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain.
- Simply, homologous series is a series of organic compounds which differ from the next compound by CH2
Example: CH3Cl, C2H5Cl, C3H7Cl, C4H9Cl etc.
- They have same general formula (As above CnH2n+1Cl).
- Two homologues differ by – CH2 unit and by mass of 14 μ.
- Homologues have same chemical properties as they have same functional groups.
- Physical properties vary gradually as melting and boiling points increase when the size of compounds increases.
Nomenclature of Carbon Compounds:
Naming a carbon compound can be done step by step by the following method –
- First, identify the number of carbon atoms.
- See if there is a functional group, indicate it with the name of the compound at either prefix or suffix.
- As we see in the case of alcohol group attached with 2 carbon chain
Ethane – ‘e’ = Ethan + ‘ol’ = Ethanol.
- Similarly for double bond “ene” and for triple bond “yne” is used.
Chemical properties of carbon compounds:
- Carbon and its compounds burn in oxygen to give carbon dioxide along with the release of heat and light.
- As carbon and its compounds on burning give a lot of heat energy so it is used as a fuel.
- Saturated hydrocarbon on burning gives a clean flame.
- Unsaturated carbon compounds on burning to give a yellow flame with lots of black smoke. This causes pollution as well as sooty deposit on the bottom of metal cooking vessels.
- Fuels such as coal and petroleum contain some amount of nitrogen and sulphur in them. Their combustion produces oxides of sulphur and nitrogen which are leading pollutants in the environment.
- On combustion, carbon and its compounds can be easily oxidized.
- Alcohol converts to carboxylic acids with the help of some oxidising agents.
- Oxidising agents: Substances that are capable of adding oxygen to other compounds are oxidising agents.
Example: Alkaline potassium permanganate or acidified potassium dichromate.
- Hydrogen is added to unsaturated hydrocarbons in the presence of catalysts such as palladium or nickel to give saturated hydrocarbon.
- Catalysts are the substance which on addition to the reaction change its rate but itself doesn’t take part in the reaction.
- In hydrogenation of vegetable oil using nickel catalyst, addition reaction is common.
- Saturated hydrocarbons are so much stable that they are fairly unreactive and don’t show any change in the presence of most reagents.
- We add chlorine to hydrocarbons during the very fast reaction in the presence of sunlight.
- One by one chlorine can replace the hydrogen atoms. Here one type of atom or a group of atoms takes the place of another, so this reaction is substitution reaction.
CH4 + Cl2 → CH3Cl + HCl (in the presence of sunlight)
Some important carbon and its compounds: Ethanol and Ethanoic Acid
Ethanol is a homologue of alkanol with molecular formula C2H5OH. It is the active ingredient of all alcoholic drinks.
Physical properties of Ethanol:
- Liquid at room temperature.
- Good solvent (soluble in water).
- Low boiling point
- Pleasant smell
Chemical properties of ethanol:
- Reaction with sodium
2Na + 2CH3CH2OH → 2 CH3CH2O – Na+ + H2
This reaction ends with the evolution of hydrogen gas (H2) and another product is sodium ethoxide.
- Reaction to give unsaturated hydrocarbon: Dehydration
Dehydration of ethanol happens when we heat ethanol at 443K adding excess concentrated H2SO4 (Sulphuric acid)[dehydrating agent], thus converted into ethene.
The functional group of carboxylic acid attached with ethane is ethanoic acid. In general, we say it acetic acid.
Physical properties of Ethanoic acid:
- Colourless liquid
- Strong vinegar-like smell.
- Highly flammable
- Volatile substance as its boiling point is 391 K.
- Freeze acetic acid looks like ice so we call it glacial acetic acid.
- Sour in taste.
Chemical properties of Ethanoic Acid:
- Esterification reaction:
When acid and alcohol reacts in the presence of acid catalysts then it dehydrates to form ester.
- Ester has a sweet smell.
- Used in making perfumes and flavouring agents.
- Reaction with a base:
Same as other acids, ethanoic acid also reacts with the base to give salt and water. Thus possess neutralization reaction.
NaOH + CH3COOH → CH3COONa + H2O
- Reaction with carbonates and hydrogencarbonates:
It reacts with carbonates and hydrogen carbonates to produce salt, CO2 and water.
2 CH3COOH + Na2CO3 → 2 CH3COONa + H2O + CO2
Soaps and Detergents:
- The molecules of soap is sodium or potassium salts of long-chain carboxylic acids.
- Soap has two ends –
Ionic end – Hydrophilic part
Long carbon chain – Hydrophobic part
- The structure of soap has a name ‘micelles‘ in which one end (carbon chain) of the molecules is towards the oil droplet while the ionic-end faces outside.
- Micelle of soap helps in dissolving the dirt in the water.
- Thus it constitutes a fair part of carbon and its compounds.
Cleansing action of soap:
- Hydrophilic end dissolves in water and the hydrophobic end dissolves in the dirt.
- These molecules form a structure inside the water like a radially outward cluster which carries the dirt from inside to surface. The formation of the cluster is the micelle.
- The oily dirt collects in the centre of the micelle after rinsing our clothes gets clean.
Detergents are ammonium or sulphonate salts of long chain carboxylic acids.
- The charged ends of detergents do not form insoluble precipitates i.e. scum.
- Detergents are also effective in hard water.
- we use detergents to make shampoos and products for cleaning clothes.
- Carbon and its compounds also includes study of detergents.