Carbon And Its Coumpound

Introduction to Carbon

Carbon is a non-metal with the symbol C. All living things, including plants and animals, are made up of carbon-based compounds.

The atomic number of carbon is 6. Its electronic configuration is:

• K Shell: 2 electrons
• L Shell: 4 electrons (Valence Shell)

Carbon always forms covalent bonds to achieve a stable electron configuration.

Covalent Bonding

A covalent bond is a chemical bond formed when pairs of electrons are shared between two atoms. It is mostly formed between two identical nonmetallic atoms or between different nonmetallic atoms.

Examples of Covalent Bonding

1. Single Bond in Hydrogen (H₂)

A Hydrogen (H) atom needs one more electron to complete its outermost shell (duplet). Two hydrogen atoms share one pair of electrons to form a single covalent bond.

2. Double Bond in Oxygen (O₂)

An Oxygen (O) atom needs two more electrons to complete its octet. Two oxygen atoms share two pairs of electrons to form a double covalent bond.

3. Triple Bond in Nitrogen (N₂)

A Nitrogen (N) atom needs three more electrons to complete its octet. Two nitrogen atoms share three pairs of electrons to form a triple covalent bond.

4. Covalent Bonding in Water (H₂O)

Oxygen needs two electrons to complete its octet, while each Hydrogen atom needs one. Therefore, one Oxygen atom shares one electron with each of two Hydrogen atoms, forming two single covalent bonds.

Physical Properties of Covalent Compounds

• Covalent compounds have low melting and boiling points because they have weak intermolecular forces.
• They are generally poor conductors of electricity because electrons are shared between atoms, meaning no free-moving charged particles (ions) are formed.

The Versatile Nature of Carbon

How Carbon Attains Noble Gas Configuration

Carbon is tetravalent (it has 4 valence electrons). It does not form ionic bonds by either losing four electrons (to form C⁴⁺) or gaining four electrons (to form C^4-).

• It is difficult for the nucleus to hold four extra electrons.
• It would require a very large amount of energy to remove four electrons.

Instead, carbon forms covalent bonds by sharing its four valence electrons with other atoms to attain a stable noble gas configuration.

Characteristic Properties of Carbon

Three characteristic properties of carbon lead to the formation of a vast number of compounds:

1. Catenation

Catenation is the unique self-linking property of an element, where atoms form long chains and rings by covalent bonds. Carbon exhibits this property to the maximum extent.

2. Tetravalency

Carbon has 4 valence electrons, so it can form four covalent bonds. It can bond with four other carbon atoms, monovalent atoms (like H, Cl), or other atoms like Oxygen, Nitrogen, and Sulphur.

3. Tendency to form Multiple Bonds

Due to its small size, carbon has a strong tendency to form multiple bonds (double and triple bonds) by sharing more than one electron pair with its own atoms or with atoms of other elements like Oxygen and Nitrogen.

Allotropes of Carbon

Allotropy is the property by which an element exists in more than one form. Each form (allotrope) has different physical properties but similar chemical properties.

Diamond

• In diamond, each carbon atom is covalently bonded to four other carbon atoms, forming a rigid 3-D tetrahedral structure.
• It is the hardest known substance.
• It is a bad conductor of electricity. This is because all four valence electrons of each carbon are used in covalent bonding, so no free electrons are left to move.
• It has a very high melting point.
• Uses: Making jewellery, cutting tools, and grinders.

Graphite

• In graphite, each carbon atom is bonded to three other carbon atoms, forming hexagonal rings in flat layers (planes).
• It is soft and slippery because these layers can slide over one another (held by weak van der Waals forces).
• It is a good conductor of electricity. Because each carbon is only bonded to three others, the fourth valence electron is free to move between the layers.
• Uses: Pencil "leads," lubricants, batteries, and cells.



Fullerene

• Fullerenes form another class of carbon allotropes.
• The first one identified was C-60, which has carbon atoms arranged in the shape of a football (a buckyball).
• It consists of 12 pentagons and 20 hexagons.

Hydrocarbons

Compounds made up of only hydrogen and carbon are called hydrocarbons.

Saturated Hydrocarbons

These are compounds of carbon which are linked only by single bonds between the carbon atoms.

Alkanes

Alkanes are saturated hydrocarbons with only C-C single bonds.
General formula: C_nH_2n+2

Example: Ethane (C₂H₆)

Unsaturated Hydrocarbons

These are compounds of carbon having double or triple bonds between their carbon atoms.

Alkenes

Alkenes are unsaturated hydrocarbons with at least one C=C double bond.
General formula: C_nH_2n

Example: Ethene (C₂H₄)

Alkynes

Alkynes are unsaturated hydrocarbons with at least one C≡C triple bond.
General formula: C_nH_2n-2

Example: Ethyne (C₂H₂)

Nomenclature

IUPAC Nomenclature of Hydrocarbons

Prefix (Root Word)

The prefix is based on the number of carbon atoms in the main chain.

No. of Carbons	Prefix	No. of Carbons	Prefix
1	Meth-	6	Hex-
2	Eth-	7	Hept-
3	Prop-	8	Oct-
4	But-	9	Non-
5	Pent-	10	Dec-

Suffix (Bond Type)

The suffix is based on the type of bond between carbon atoms.

• -ane for Single Bond (Alkanes)
• -ene for Double Bond (Alkenes)
• -yne for Triple Bond (Alkynes)

Examples:

• CH₃-CH₂-CH₃: 3 Carbons (Prop-) + Single Bonds (-ane) = Propane
• CH₃-CH=CH₂: 3 Carbons (Prop-) + Double Bond (-ene) = Propene
• CH₃-C≡CH: 3 Carbons (Prop-) + Triple Bond (-yne) = Propyne

Carbon Compounds on the Basis of Structure

1. Straight (unbranched) chain: e.g., Propane (CH₃-CH₂-CH₃)
2. Branched chain: e.g., Isobutane
3. Cyclic (ring) chain: e.g., Cyclohexane

Functional Groups

An atom or group of atoms that makes a carbon compound reactive and decides its chemical properties is called a functional group.

Functional Group	Family	Suffix / Prefix
-OH	Alcohol	-ol (Suffix)
-CHO	Aldehyde	-al (Suffix)
-CO-	Ketone	-one (Suffix)
-COOH	Carboxylic Acid	-oic acid (Suffix)
-Cl or -Br	Halogen	chloro-, bromo- (Prefix)

Steps of Nomenclature (with Functional Groups)

1. Step 1: Identify the number of carbon atoms in the longest continuous chain. This gives the Root Word (Meth, Eth, Prop, etc.).
2. Step 2: Identify the type of C-C bond (single, double, triple). This gives the primary Suffix (-ane, -ene, -yne).
3. Step 3: Identify the functional group. This gives the main Suffix (-ol, -al, -oic acid) or a Prefix (Chloro-, Bromo-).

Chapter 7: Homologous Series

A homologous series is a series of carbon compounds in which the same functional group substitutes for hydrogen and successive members differ by a CH₂ group.

Example (Alcohols): CH₃OH (Methanol), C₂H₅OH (Ethanol), C₃H₇OH (Propanol)...

Properties of a Homologous Series

• All members are represented by the same general formula.
• Any two adjacent members differ by one carbon atom and two hydrogen atoms (a -CH₂ group).
• Any two adjacent members differ by a molecular mass of 14u.
• All members show similar chemical properties (due to the same functional group).
• Physical properties (like melting point, boiling point) show a gradual change as molecular mass increases.

Chemical Properties of Carbon Compounds

1. Combustion

Combustion is a chemical reaction in which a substance burns in oxygen to give out heat and light.

2. Oxidation

Alcohols can be converted to carboxylic acids in the presence of an oxidizing agent, such as alkaline KMnO₄ (potassium permanganate) or acidified K₂Cr₂O₇ (potassium dichromate).

3. Addition Reaction (Hydrogenation)

Unsaturated hydrocarbons (alkenes/alkynes) add hydrogen in the presence of a catalyst (like Ni or Pd) to give saturated hydrocarbons (alkanes). This is called a hydrogenation reaction.

Use: This process is used to convert liquid vegetable oils (unsaturated fats) into solid vegetable ghee (saturated fats).

4. Substitution Reaction

A reaction in which one atom or functional group in a chemical compound is replaced by another atom or functional group.

Important Carbon Compounds

Ethanol (CH₃CH₂OH)

Physical Properties of Ethanol

• Colourless liquid with a pleasant smell and burning taste.
• Soluble in water.
• Commonly called alcohol and is the active ingredient in alcoholic drinks.
• It is a good solvent, so it is used in medicines like tincture iodine, cough syrups, and tonics.

Chemical Properties of Ethanol

1. Reaction with Sodium:

This reaction is used as a test for ethanol, as the evolution of hydrogen (H₂) gas causes a "pop" sound when a flame is brought near.

2. Dehydration:

Hot concentrated H₂SO₄ acts as a powerful dehydrating agent, removing a molecule of water from ethanol.

Ethanoic Acid (CH₃COOH)

Physical Properties of Ethanoic Acid

• Commonly known as acetic acid.
• A solution of 5-8% acetic acid in water is called vinegar, which is used as a preservative in pickles.
• The melting point of pure ethanoic acid is 290 K (17°C).
• It is a weak acid.

Chemical Properties of Ethanoic Acid

1. Esterification Reaction:

The reaction of a carboxylic acid and an alcohol (in the presence of an acid catalyst) to form an ester.

Esters are sweet-smelling substances, used in making perfumes and as flavouring agents.

2. Saponification Reaction:

An ester reacts with a base (like NaOH) to form an alcohol and the sodium salt of the carboxylic acid (which is soap).

3. Reaction with Base (Neutralisation):

4. Reaction with Carbonates and Hydrogen Carbonates:

Soaps and Detergents

Soap

A soap is the sodium or potassium salt of a long-chain carboxylic acid (fatty acid). Example: C₁₇H₃₅COO^-Na⁺ (Sodium stearate).

A soap molecule has two parts:

• An ionic, hydrophilic part (water-loving) - the COO^-Na⁺ head.
• A long hydrocarbon chain, which is hydrophobic (water-repelling) - the tail.

Cleansing Action of Soap

Most dirt is oily (non-polar) and does not dissolve in water (polar).

1. When soap is added to water, the soap molecules form clusters called micelles.
2. In a micelle, the hydrophobic tails point inwards, dissolving the oil or dirt particle.
3. The hydrophilic heads point outwards, remaining in contact with the water.
4. This forms an emulsion. When the fabric is agitated (scrubbed) or rinsed, the micelles containing the dirt are lifted away and washed away with the water.

Detergents

Detergents are generally ammonium or sulphonate salts of long-chain carboxylic acids. They have a similar cleansing action to soaps.

Hard Water and Scum

Hard water contains dissolved minerals, specifically calcium (Ca²⁺) and magnesium (Mg²⁺) ions.

When soap is used in hard water, the Ca²⁺ and Mg²⁺ ions react with the soap molecules to form an insoluble product called scum. This scum sticks to the clothes and prevents effective cleaning.

Detergents do not form insoluble scum with hard water. The calcium and magnesium salts of detergents are soluble in water.