Carbon and its Compounds:

Before we read carbon and its compounds. There are two types of compounds:

1. Organic compounds: Any compounds that contain carbon are organic compounds.
2. Inorganic compounds: Compounds which don’t contain carbon are inorganic compounds.

Covalent Bond:

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:

1. Catenation:

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.

2. Tetravalency:

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.

Hydrocarbon:

• 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:

1. Saturated 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 C_nH_2n+2
• In saturated hydrocarbons, all the single bonds are satisfied thus forms a stable compound.
• Examples are Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈) etc.

2. Unsaturated Hydrocarbon:

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 C_nH_2n
• Alkynes are also unsaturated hydrocarbons.
• Denoted by – C ≡ C –
• It contains one or more triple bond in the compound.
• General Formula is C_nH_2n-2

 

Types of chains formed by carbon and its compounds:

1. Straight chain i.e. unbranched chain:

In this type of chain 1^st 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.

Functional group:

• 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:

Heteroatom	Functional group	Formula of functional group
Cl/Br	Halo- (Chloro/bromo)	-Cl, – Br
Oxygen	1. Alcohol	—OH
	2. Aldehyde
	3. Ketone
	4. Carboxylic acid

Homologous series:

• 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 C_nH_2n+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 –

1. First, identify the number of carbon atoms.
2. See if there is a functional group, indicate it with the name of the compound at either prefix or suffix.
3. As we see in the case of alcohol group attached with 2 carbon chain

Ethane – ‘e’ = Ethan + ‘ol’ = Ethanol.

4. Similarly for double bond “ene” and for triple bond “yne” is used.

Chemical properties of carbon compounds:

Combustion:

• 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.

Oxidation:

• 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.

Addition Reaction:

• 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.

Substitution Reaction:

• 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:

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).
• Colourless
• 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.

Ethanoic acid:

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:

1. 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.

2. 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

3. 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:

Soaps:

• 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:

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.

To practice Question and answer related to this chapter, please click here  Q/A on Carbon and Its Compounds