Carbon and its Compounds

Carbon

Carbon is a chemical element with the symbol "C" and the atomic number 6, which means it has six protons in its nucleus. It is one of the fundamental building blocks of life on Earth and plays a central role in the chemistry of all living organisms. Carbon is incredibly versatile and forms the basis of a vast number of compounds due to its unique atomic structure and bonding properties. Some key characteristics and properties of carbon are:

Atomic Structure

1. Carbon atoms have six electrons, arranged in two electron shells around the nucleus.
2. In its ground state, a carbon atom has two electrons in its innermost shell (the K shell) and four electrons in the outermost shell (the L shell).

Carbon Always Forms Covalent Bonds

1. Carbon is a non-metal element with an atomic number of 6, indicating that a neutral carbon atom has 6 electrons.
2. To achieve stability, an atom typically aims for a full outer electron shell, often with 8 electrons. Carbon, with 4 electrons in its outermost shell, can neither easily lose nor gain 4 electrons to attain this stable configuration.
3. Due to its small size and the strong attraction of its nucleus for its outer electrons, carbon atoms prefer to share electrons rather than transfer them. This electron sharing leads to the formation of covalent bonds.
4. Covalent bonds involve the sharing of electron pairs between carbon atoms and other elements, allowing each atom to achieve a more stable electron configuration.

Carbon is Tetravalent

1. Carbon has a valency of 4. Valency refers to the number of bonds an atom can form with other atoms. In carbon's case, it can form up to 4 covalent bonds with other atoms.
2. This tetravalency is a result of carbon having 4 electrons in its outermost shell. It needs 4 more electrons to attain a stable configuration with 8 electrons in its outer shell.
3. Carbon achieves this stability by sharing its 4 outer electrons with other atoms, allowing it to bond with multiple atoms simultaneously.

Self-Combination (Catenation)

1. One of the most remarkable properties of carbon is its ability to combine with itself, forming long chains or rings of carbon atoms.
2. Carbon atoms can bond to one another repeatedly, creating extended structures. This property is called catenation.
3. These carbon chains and rings serve as the backbone for a wide variety of organic compounds. The ability to form diverse carbon-carbon bonds results in an extensive array of carbon-based molecules.
4. Catenation is fundamental to the vast diversity of organic chemistry, as it allows for the creation of complex, large, and diverse organic molecules, from simple hydrocarbons to complex biomolecules like DNA and proteins.

Allotropes of Carbon

Allotropes of carbon refer to the different physical forms in which carbon atoms can arrange themselves to create unique structures. Despite being composed of the same element, carbon, these allotropes have distinct properties due to their differing atomic arrangements. The three most well-known allotropes of carbon are diamond, graphite, and graphene. Here's an explanation of each:

Diamond

1. Structure: Diamond consists of a three-dimensional crystal lattice structure, where each carbon atom forms strong covalent bonds with four other carbon atoms, creating a tetrahedral arrangement. This results in a network of interconnected carbon atoms.



2. Properties:

• Hardness: Diamond is renowned for its extreme hardness, making it the hardest naturally occurring material.
• Transparency: Diamonds are transparent and exhibit exceptional brilliance due to their ability to refract and reflect light.
• Electrical Conductivity: Diamond is an insulator; it does not conduct electricity because all valence electrons are used in covalent bonds.
• Applications: Diamonds are highly valued as gemstones, but they are also used in industrial applications like cutting, drilling, and grinding due to their hardness.

Graphite

1. Structure: Graphite consists of stacked layers of hexagonal rings of carbon atoms. Each carbon atom forms strong covalent bonds with three neighbouring carbon atoms within a layer, creating a hexagonal pattern. Weak Van der Waals forces hold these layers together.



2. Properties:

• Lubrication: Graphite is soft and slippery, making it an effective dry lubricant for machinery.
• Electrical Conductivity: Graphite is an excellent conductor of electricity due to the presence of delocalised (free-moving) electrons between layers.
• Applications: It is used in pencils (the "lead" is a mix of graphite and clay), as an anode material in batteries, and in various industrial applications where lubrication and conductivity are essential.

Graphene

1. Structure: Graphene is a single layer of carbon atoms arranged in a hexagonal lattice, similar to a single layer of graphite. Each carbon atom forms strong covalent bonds with three neighbouring carbon atoms.



2. Properties:

• Exceptional Strength: Graphene is incredibly strong and has a tensile strength many times greater than steel.
• High Electrical Conductivity: It is an excellent conductor of electricity, and its electrons move freely within the two-dimensional lattice.
• Transparency: Graphene is transparent and allows visible light to pass through.
• Applications: Graphene holds great promise in various fields, including electronics, materials science, and nanotechnology, due to its exceptional properties. It is being explored for applications in electronics, sensors, and even medical devices.

Buckminsterfullerene (C60)

• Structure: Buckminsterfullerene, often referred to as "buckyballs," consists of 60 carbon atoms arranged in a hollow sphere. These atoms form interlocking hexagonal and pentagonal rings, much like the pattern on a soccer ball.



• Properties:

1. Spherical Shape: Buckminsterfullerene has a spherical shape with a distinctive arrangement of carbon atoms.
2. Stability: It is a stable molecule with well-defined properties.
3. Solubility: Buckminsterfullerene can be dissolved in some organic solvents.
4. Properties: Other physical and chemical properties of buckminsterfullerene are still being studied due to its relatively recent discovery.
5. Applications: While its applications are still being explored, buckminsterfullerene is of interest in fields like materials science, nanotechnology, and drug delivery systems. Its unique structure makes it suitable for encapsulating other molecules, potentially enabling targeted drug delivery.

Covalent Bonding

Covalent bonding is a type of chemical bonding that occurs when two or more atoms share electrons to achieve a more stable electron configuration. In covalent bonds, non-metal atoms typically interact with each other. The primary goal of covalent bonding is to fill the outermost electron shell (valence shell) of each atom with electrons, similar to the electron configuration of noble gases.

1. Electron Sharing: When non-metal atoms come close to each other, their outermost electrons interact. Each atom contributes some of its outermost electrons for sharing with the other atom(s).
2. Stable Configuration: By sharing electrons, both atoms achieve a stable electron configuration with a full outermost shell, typically containing eight electrons (octet rule). Hydrogen atoms are an exception; they aim for two electrons in their outermost shell.
3. Formation of Covalent Bond: The electrons that are shared between the atoms create a bond known as a covalent bond. This bond holds the atoms together in a molecule.

Types of Covalent Bonds

Covalent bonds can be categorised into three types based on the number of electron pairs shared between the participating atoms:

1. Single Covalent Bond: In a single covalent bond, two atoms share one pair of electrons. This bond is represented as a single line (e.g., H₂, Cl₂). Each atom contributes one electron to the shared pair.



2. Double Covalent Bond: A double covalent bond involves the sharing of two pairs of electrons between two atoms. This bond is represented by a double line (e.g., O₂). Each atom contributes two electrons to form two shared pairs.



3. Triple Covalent Bond: A triple covalent bond is formed when two atoms share three pairs of electrons. It is represented by a triple line (e.g., N₂). Each atom contributes three electrons to create three shared pairs.

Organic Compounds

Organic compounds are a class of chemical compounds primarily composed of carbon and hydrogen atoms, often with the addition of other elements such as oxygen, nitrogen, sulphur, and halogens. These compounds play a crucial role in living organisms and are essential for life processes. Some key characteristics of organic compounds are:

1. Composition: Organic compounds are predominantly composed of carbon (C) and hydrogen (H) atoms. Other elements, such as oxygen (O), nitrogen (N), sulphur (S), phosphorus (P), and halogens (e.g., chlorine, bromine), can also be part of organic compounds.
2. Carbon Backbone: Carbon atoms are the backbone of organic molecules. They can form a variety of structures, including long chains, branched chains, and closed rings, by bonding with other carbon atoms, giving rise to the immense diversity of organic compounds. This unique property is known as "catenation."
3. Functional Groups: Organic compounds are classified into various types based on their functional groups. A functional group is a specific arrangement of atoms within a molecule that imparts specific chemical properties to that molecule. Common functional groups include hydroxyl (OH), carbonyl (C=O), carboxyl (COOH), amino (NH2), and many more.
4. Hydrocarbons: Many organic compounds are hydrocarbons, meaning they consist exclusively of carbon and hydrogen atoms.
5. Low Melting and Boiling Points: Organic compounds generally have lower melting and boiling points compared to many inorganic compounds. This is due to the weak intermolecular forces between organic molecules.
6. Non-Conductors: Most organic compounds are non-conductors of electricity because they do not contain ions. Their electrons are shared in covalent bonds, preventing the flow of electrical current.

Hydrocarbons

Hydrocarbons are organic compounds composed of hydrogen (H) and carbon (C) atoms. They are the simplest class of organic compounds and are the building blocks of many other organic molecules.

There are two main types of hydrocarbons: Aliphatic and aromatic hydrocarbons.

I. Aliphatic Hydrocarbons

These hydrocarbons have straight or branched-chain structures and can be further classified into two subcategories:

1. Saturated Hydrocarbons

Alkanes:

1. These hydrocarbons contain only single covalent bonds between carbon atoms. They are referred to as saturated because they have the maximum number of hydrogen atoms attached to each carbon atom.
2. The general formula for alkanes is C_nH_2n+2, where "n" represents the number of carbon atoms in the molecule.
3. Alkanes can form straight-chain or branched-chain structures. The arrangement of carbon atoms and hydrogen atoms can vary within this family of hydrocarbons.
4. Examples: Methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and so on.

2. Unsaturated Hydrocarbons

Alkenes:

1. These hydrocarbons contain at least one carbon-carbon double bond (C=C). They are referred to as unsaturated because they do not have the maximum number of hydrogen atoms attached to each carbon atom.
2. The general formula for alkenes is C_nH_2n.
3. Alkenes can also form straight-chain or branched-chain structures. The presence of a double bond results in restricted rotation around that bond.
4. Examples: Ethene (ethylene, C₂H₄), propene (propylene, C₃H₆), and so on.

Alkynes:

1. Alkynes contain at least one carbon-carbon triple bond. Like alkenes, they are unsaturated hydrocarbons with fewer hydrogen atoms compared to alkanes.
2. The general formula for alkynes is C_nH_2n-2.
3. Alkynes can form straight-chain or branched-chain structures. The presence of a triple bond also results in restricted rotation around that bond.
4. Examples: Ethyne (acetylene, C₂H₂), propyne (C₃H₄), and so on.

II. Aromatic Hydrocarbons

Aromatic hydrocarbons, also known as cyclic hydrocarbons, are a special class of unsaturated hydrocarbons known for their distinctive ring-like structure called an aromatic ring or benzene ring. The most famous aromatic hydrocarbon is benzene (C₆H₆), but there are many other compounds with similar structures.

Nomenclature of Hydrocarbons

Naming hydrocarbons follows a systematic set of rules established by the International Union of Pure and Applied Chemistry (IUPAC). These rules are designed to provide a standardised and unambiguous way to name organic compounds. The nomenclature of hydrocarbons primarily depends on the type of hydrocarbon (alkane, alkene, or alkyne) and the structure of the molecule.

Structural Isomers

Isomers are compounds that have the same molecular formula, which means they have the same types and numbers of atoms but different structural arrangements or connectivity of atoms. In other words, structural isomers are different compounds with distinct chemical structures, even though they share the same chemical formula.

Key points to understand about structural isomers are:

1. Same Molecular Formula: Structural isomers have identical numbers and types of atoms (the same molecular formula). This means they have the same ratio of elements.
2. Different Structural Arrangements: The defining feature of structural isomers is that their atoms are arranged differently within the molecule. This different arrangement can result in a variety of structural changes, such as branching of carbon chains, ring formations, or different functional group positions.
3. Distinct Chemical Properties: Because of their different structural arrangements, structural isomers often exhibit different physical and chemical properties. These differences can include variations in melting and boiling points, solubility, reactivity, and biological activities.
4. Importance: Structural isomerism is a fundamental concept in organic chemistry because it highlights the significance of the arrangement of atoms within a molecule. Even a small change in connectivity can result in entirely different chemical behaviours and properties.

Examples:

A classic example of structural isomerism can be seen in the compounds with the molecular formula C₄H₁₀. There are two structural isomers with this formula: n-butane (normal butane) and isobutane (or iso-butane). These isomers have different structural arrangements, with n-butane having a straight-chain structure, while isobutane has a branched structure.

Hexane (C₆H₁₄) is a hydrocarbon with six carbon atoms and 14 hydrogen atoms. It is a straight-chain alkane, and it can have several structural isomers due to the different ways its carbon atoms can be arranged within a molecule.

Functional Groups

Functional groups are specific groups of atoms or bonds within organic molecules that are responsible for the molecule's chemical reactions and properties. They are the reactive centres of organic compounds and play a crucial role in defining the compound's function and reactivity. Functional groups determine how a molecule will interact with other molecules, undergo chemical reactions, and exhibit specific properties.

Homologous Series

A homologous series in organic chemistry is a group of organic compounds that have similar structural features and chemical properties. These compounds share the same functional group and exhibit a gradual change in their physical properties as the number of carbon atoms in their molecules increases.

Key characteristics of a homologous series include:

1. Same General Formula: All members of a homologous series can be represented by the same general chemical formula. This formula describes the relationship between the number of carbon (C) and hydrogen (H) atoms in the molecules.
2. Structural Similarity: Compounds within a homologous series have similar structures, with variations arising from differences in the number of carbon atoms in the main carbon chain or the functional group attached to it.
3. Gradual Change in Physical Properties: As you move from one member of the series to the next, there is a gradual change in physical properties such as boiling points, melting points, and densities. This change is primarily due to the increase in molecular mass.
4. Chemical Similarity: Members of a homologous series exhibit similar chemical properties because they share a common functional group. They often undergo similar types of chemical reactions.
5. Differ by a CH₂ Group: Each successive member of the series differs from the previous one by the addition of a CH₂ group (methylene group). This addition increases both the molecular mass and the number of carbon and hydrogen atoms in the molecule.
6. Difference in Molecular Mass: The difference in molecular mass between any two adjacent homologues in the series is typically constant. This difference is usually 14 atomic mass units (u) for hydrocarbon homologous series.

Examples of Homologous Series

1. Alkanes: These are hydrocarbons with single bonds and have the general formula C_nH_2n+2, where n is the number of carbon atoms.

Examples:

• Methane (CH₄)
• Ethane (C₂H₆)
• Propane (C₃H₈)

2. Alkenes: These are hydrocarbons with at least one carbon-carbon double bond and have the general formula C_nH_2n.

Examples:

• Ethene (Ethylene) (C₂H₄)
• Propene (Propylene) (C₃H₆)
• Butene (Butylene) (C₄H₈)

3. Alkynes: These are hydrocarbons with at least one carbon-carbon triple bond and have the general formula C_nH_2n-2.

Examples:

• Ethyne (Acetylene) (C₂H₂)
• Propyne (C₃H₄)
• Butyne (C₄H₆)

4. Haloalkane: These contain a halogen atom (Cl, Br, or I) bonded to carbon and have the general formula C_nH_2n+1X.

Examples:

• Chloromethane (CH₃Cl)
• Bromoethane (C₂H₅Br)
• Iodoethane (C₂H₅I)

5. Alcohols: These contain the -OH functional group and have the general formula C_nH_2n+1OH.

Examples:

• Methanol (CH₃OH)
• Ethanol (C₂H₅OH)
• Propanol (C₃H₇OH)

6. Aldehydes: These contain the carbonyl group (C=O) at the end of a carbon chain and have the general formula C_nH_2n+1CHO.

Examples:

• Methanal (Formaldehyde) (CH₂O)
• Ethanal (Acetaldehyde) (C₂H₄O)
• Propanal (C₃H₆O)

7. Ketones: These contain the carbonyl group (C=O) within the carbon chain and have the general formula C_nH_2nO.

Examples:

• Propanone (Acetone) (C₃H₆O)
• Butanone (Methyl Ethyl Ketone) (C₄H₈O)
• Pentan-3-one (C₅H₁₀O)

8. Carboxylic Acids: These contain the carboxyl group (-COOH) and have the general formula C_nH_2n+1COOH.

Examples:

• Methanoic Acid (Formic Acid) (HCOOH)
• Ethanoic Acid (Acetic Acid) (CH₃COOH)
• Propanoic Acid (C₂H₅COOH)

Chemical Properties of Carbon Compounds

Chemical properties of carbon compounds are characteristics and behaviours that carbon-containing molecules exhibit when they undergo chemical reactions. These properties are crucial for understanding the behaviour and reactivity of organic compounds. Here are some important chemical properties of carbon compounds:

Combustion

Carbon compounds can burn in the presence of oxygen to produce carbon dioxide (CO₂) and water vapour (H₂O), along with the release of energy in the form of heat and sometimes light.

For example: CH₄ (methane) + 2O₂ → CO₂ + 2H₂O + Heat + Light
This property makes many carbon compounds excellent fuels.

Oxidation

Carbon compounds, especially organic compounds, can undergo oxidation reactions. Oxidation typically involves the addition of oxygen or the removal of hydrogen from a molecule.
For instance, alcohols can be oxidised to form aldehydes, and aldehydes can further be oxidised to carboxylic acids in the presence of oxidising agents like potassium permanganate.

Addition Reactions

Unsaturated carbon compounds, such as alkenes and alkynes, can participate in addition reactions. These reactions involve the addition of atoms or groups of atoms to the carbon-carbon double or triple bonds.
Common examples include the hydrogenation of alkenes, where hydrogen gas (H₂) is added in the presence of catalysts like nickel or palladium to produce saturated hydrocarbons.

Substitution Reactions

In substitution reactions, one or more hydrogen atoms in a molecule are replaced by different atoms or groups of atoms. Saturated hydrocarbons (alkanes) are known for their substitution reactions.
For instance, when methane (CH₄) reacts with chlorine (Cl₂) in the presence of sunlight, it undergoes a substitution reaction to form chloromethane (CH₃Cl) and hydrogen chloride (HCl).

CH₄ + Cl₂ + Sunlight → CH₃Cl + HCl

Some Important Compounds

1. Ethanol

1. Common Name: Ethanol is commonly known as ethyl alcohol.
2. Chemical Formula: Its chemical formula is C₂H₅OH, which means it consists of two carbon atoms, six hydrogen atoms, and one oxygen atom.
3. Properties of Ethanol:

• Physical State: Ethanol is a clear, colourless, and volatile liquid at room temperature. It has a slightly sweet odour and taste. It has a relatively low melting point and boiling point, which allows it to exist as a liquid under normal conditions.
• Use in Alcoholic Drinks: Ethanol is the active ingredient in alcoholic beverages such as beer, wine, and spirits. These beverages are consumed for recreational and social purposes.
• Solubility: Ethanol is highly soluble in water, and it can mix with water in all proportions. This property is essential in the production of various alcoholic drinks and pharmaceutical solutions.
• Medical Uses: Ethanol is used in medicines such as tincture iodine, cough syrups, and tonics. However, its consumption in excessive quantities can have harmful effects on health.

Reactions of Ethanol:

1. Reaction with Sodium: When ethanol reacts with sodium (Na), it produces sodium ethoxide (2CH₃CH₂ONa). This reaction also generates hydrogen gas.
   The evolution of hydrogen gas is a characteristic test for the presence of ethanol.
   2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa + H₂
2. Dehydration Reaction: Heating ethanol at around 443 K with excess concentrated sulfuric acid (H₂SO₄) leads to the dehydration of ethanol, producing ethene (CH₂=CH₂) and water (H₂O).
   Concentrated sulfuric acid serves as a dehydrating agent, removing water from ethanol in this reaction.

2. Ethanoic Acid (Acetic Acid)

1. Common Name: Ethanoic acid is commonly known as acetic acid.
2. Chemical Formula: Its chemical formula is CH₃COOH, which means it consists of two carbon atoms, four hydrogen atoms, and two oxygen atoms.
3. Properties of Ethanoic Acid:

• Physical State: Ethanoic acid is a colourless liquid with a strong, pungent smell and a sour taste.
• Occurrence: Ethanoic acid can be found in a diluted form in vinegar, where it acts as a preservative for pickles. Pure ethanoic acid has a freezing point of 290 K, which can lead to it freezing during cold winters, giving rise to the name "glacial acetic acid."
• Weak Acidity: Carboxylic acids like ethanoic acid are considered weak acids. Unlike strong mineral acids like hydrochloric acid (HCl), carboxylic acids do not ionise completely in solution.

Reactions of Ethanoic Acid:

1. Esterification Reaction: Ethanoic acid can undergo esterification reactions, where it reacts with an alcohol, such as absolute ethanol, in the presence of an acid catalyst to form an ester. Esters are often sweet-smelling substances and find use in perfumes and flavouring agents.
   

   When treated with sodium hydroxide (NaOH), an alkali, esters can be converted back to alcohol and the sodium salt of the carboxylic acid. This process is known as saponification and is used in soap production.

2. Reaction with a Base: Ethanoic acid, like mineral acids, reacts with bases such as sodium hydroxide (NaOH) to produce salt (sodium ethanoate or sodium acetate) and water.
   The reaction is as follows: NaOH + CH₃COOH → CH₃COONa + H₂O
3. Reaction with Carbonates and Hydrogencarbonates: Ethanoic acid reacts with carbonates (e.g., sodium carbonate) and hydrogencarbonates (e.g., sodium hydrogencarbonate) to produce a salt (sodium acetate), carbon dioxide (CO₂), and water.
   The reaction is similar for both types of compounds:

• For sodium carbonate:
  2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
• For sodium hydrogencarbonate:
  CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

Soap and Detergents

Soap and detergents are both cleansing agents used for various cleaning purposes, but they have different compositions and properties. Here's an explanation of soap and detergents:

Soap

1. Composition: Soap is typically the sodium or potassium salt of long-chain carboxylic acids, known as fatty acids. The most common sources of these fatty acids are animal fats and vegetable oils.
2. Structure: A soap molecule consists of two main parts:
   
   A long hydrocarbon chain: This part is hydrophobic (water-repelling) and is insoluble in water but soluble in oil and grease.
   A short ionic part: This part is hydrophilic (water-attracting) and is soluble in water but insoluble in oil. It typically carries a negative charge (anion), such as COO^-Na⁺ (sodium salt of the carboxyl group).



3. Cleansing Action: Soaps work by forming structures called micelles in water. Micelles are spherical aggregates of soap molecules in which the hydrocarbon tails are directed inward and the ionic heads are directed outward, surrounded by water molecules. When you wash something with soap, the hydrophobic tails of soap molecules attach to oil and grease (dirt) on the surface, while the hydrophilic heads remain in contact with water. This allows the dirt to be lifted off the surface and rinsed away with water.



4. Advantages: Soaps are biodegradable and environmentally friendly. They are effective cleansers for most purposes, especially when used with soft water.

Detergents

1. Composition: Detergents are synthetic cleansing agents. They are typically sodium salts of long-chain benzene sulfonic acids or alkyl hydrogensulphates. Unlike soaps, detergents are not derived from natural sources like fats and oils.
2. Structure: Similar to soaps, detergent molecules consist of a long hydrocarbon chain (hydrophobic) and a short ionic part (hydrophilic), which can be sulfonate (SO₃^-Na⁺) or sulphate (SO₄^-Na⁺), depending on the type of detergent.
3. Cleansing Action: Detergents function similarly to soaps by forming micelles in water. These micelles also trap oil, grease, and dirt, allowing them to be rinsed away with water. Detergents have the added advantage of being effective even in hard water, as they do not form insoluble precipitates with calcium and magnesium ions found in hard water.
4. Advantages: Detergents have several advantages over soaps:

• They can be used with both hard and soft water.
• They provide a stronger cleansing action than soaps.
• Some detergents are formulated to work well in specific conditions, such as high-efficiency (HE) detergents for washing machines.

Environmental Impact of Soaps and Detergents

1. Soaps are generally biodegradable and environmentally friendly, as they can be broken down by natural processes.
2. Some detergents, especially older formulations, may not be biodegradable, which can lead to water pollution if not properly managed. However, many modern detergents are designed to be more environmentally friendly.