Carbon and its Compounds-Notes

A covalent bond is formed when two atoms share one or more pairs of electrons to achieve a more stable electron configuration, typically following the octet rule. The sharing of electrons allows each atom involved in the bond to fill its outermost shell, achieving greater stability. This type of bond is especially significant in carbon due to its unique electron configuration.

Carbon’s Electron Configuration

Carbon, with the atomic number 6, has an electron configuration of \(1s^22s^22p^2\). This means carbon has four electrons in its outermost shell, which can hold a total of eight electrons. To complete its octet and achieve stability, carbon needs to share its four valence electrons with other atoms. This ability to form four bonds is what makes carbon such a versatile element in forming a wide range of compounds.

Formation of Covalent Bonds in Carbon Compounds

• Single Covalent Bond \((\ce{C-C})\):
  A single covalent bond forms when one pair of electrons is shared between two atoms. For example, in a molecule of methane \(\ce{CH4}\), each hydrogen atom shares one electron with the carbon atom. Since carbon needs four electrons to complete its octet, it forms four single covalent bonds with four hydrogen atoms.
• Double and Triple Covalent Bonds \(\ce{(C=C)} \text{ and }\ce{(C#C)}\):
  In certain compounds, carbon atoms can form multiple bonds to achieve stability. For instance, in ethene \((\ce{C2H4})\), two carbon atoms are connected by a double covalent bond, where two pairs of electrons are shared. Similarly, in ethyne \((\ce{C2H2})\), a triple bond forms when three pairs of electrons are shared between two carbon atoms. These multiple bonds contribute to the strength and rigidity of the molecules.
• Coordinate Covalent Bond:
  A coordinate covalent bond occurs when both electrons in a shared pair come from the same atom. This type of bond is seen in compounds like ammonium ion \(\ce{NH4^+}\), where the nitrogen atom donates both electrons to form a bond with a hydrogen ion. Carbon can also participate in coordinate bonding, although it is more commonly involved in regular covalent bonding.

Properties of Covalent Compounds

Carbon compounds, such as those formed through covalent bonding, exhibit distinct properties:

• Low Melting and Boiling Points:
  Most covalent compounds have low melting and boiling points, as the forces between molecules are relatively weak compared to the ionic bonds in salts.
• Poor Electrical Conductivity:
  Since covalent compounds do not have free-moving charged particles (such as ions or electrons), they typically do not conduct electricity.
• Solubility:
  Covalent compounds are often soluble in non-polar solvents like benzene but are insoluble in water, a polar solvent. However, there are exceptions like alcohols that exhibit polar characteristics.

Carbon has four valence electrons in its outer shell (configuration: \(1s^22s^2 2p^2\)). To attain stability, it can share these four electrons with other atoms, forming up to four covalent bonds. This ability to bond with many different elements and with other carbon atoms allows it to form an extraordinary variety of molecules with diverse structures and properties. The strength and stability of carbon-carbon bonds, along with its bonding flexibility, make it highly adaptable in forming both simple and complex compounds.

Key Reasons for Carbon's Versatility

• Covalent Bonding:
  Carbon atoms form strong covalent bonds with other atoms, which are stable and can be single, double, or triple bonds. The flexibility in bonding enables carbon to create a vast array of structures—chains, branches, rings, and even complex networks.
• Formation of Multiple Bonds:
  Carbon can form double or triple bonds with other elements, particularly with oxygen, nitrogen, and other carbon atoms. For example, in ethene \((\ce{C2H4})\), carbon forms a double bond with another carbon atom, and in ethyne \((\ce{C2H2})\), a triple bond is formed. This capacity to form multiple bonds increases the variety of molecules carbon can form.
• Tetravalency:
  The tetravalency of carbon allows it to bond with up to four different atoms, leading to the formation of diverse organic molecules like alkanes, alkenes, alkynes, and aromatic compounds. This tetravalency is key to forming long carbon chains, essential in organic chemistry.
• Catenation:
  Carbon has a unique ability to bond with other carbon atoms to form long chains or rings. This property is known as catenation. It enables the formation of complex carbon compounds like plastics, natural polymers, and even the backbone of DNA, the molecule responsible for life’s genetic code.
• Isomerism:
  Due to its ability to form different structural arrangements, carbon compounds exhibit isomerism. Isomers are compounds that have the same molecular formula but different structural arrangements, leading to different properties. For example, butane and isobutane are isomers of C₄H₁₀, and their properties differ significantly despite having the same number of carbon and hydrogen atoms.

Saturated Carbon Compounds

Saturated carbon compounds are those in which all carbon atoms are connected by single covalent bonds. These compounds are "saturated" with hydrogen atoms, meaning each carbon atom is bonded to as many hydrogen atoms as possible. Because of the single bonds, saturated compounds do not have any double or triple bonds.

Characteristics of Saturated Compounds:

• Single Bonds:
  The defining feature of saturated compounds is the presence of single bonds between carbon atoms. Each carbon atom shares one pair of electrons with another carbon atom, forming a strong and stable bond.
• Alkanes:
  Saturated hydrocarbons are also known as alkanes. They are the simplest type of hydrocarbons. The general formula for alkanes is \(C_nH_{2n+2}\) (where \(n\) is the number of carbon atoms).
• Stability:
  Saturated compounds are generally stable and less reactive than unsaturated compounds. This is due to the strong single bonds between carbon atoms.
• Physical Properties:
  aturated hydrocarbons tend to have higher melting and boiling points compared to unsaturated compounds. They are often solid at room temperature (like paraffin wax) or liquid (like octane in gasoline).

Examples of Saturated Compounds

• Methane \((\ce{CH4})\):
  The simplest alkane, consisting of one carbon atom bonded to four hydrogen atoms. Methane is a major component of natural gas



• Ethane \((\ce{C2H6})\):
  A two-carbon alkane commonly found in natural gas.



• Butane \((\ce{C4H10})\):
  Used in fuel for lighters and in liquefied petroleum gas (LPG).

Reactivity

Saturated hydrocarbons tend to undergo reactions like combustion (burning) or substitution reactions but do not participate in addition reactions (which are typical of unsaturated compounds).

Unsaturated Carbon Compounds

Unsaturated carbon compounds, on the other hand, contain at least one double bond or triple bond between carbon atoms. These compounds are not "saturated" with hydrogen atoms because the presence of double or triple bonds leaves space for additional atoms to bond.

Types of Unsaturated Compounds

• Alkenes:
  hese are hydrocarbons that contain at least one double bond between two carbon atoms. The general formula for alkenes is \(C_nH_{2n}.\) Because of the double bond, alkenes are more reactive than alkanes.
  
  Example:
  Ethene \((\ce{C2H4})\) is a simple alkene where two carbon atoms are double-bonded to each other, and each carbon atom is bonded to two hydrogen atoms.
• Alkynes:
  These compounds contain at least one triple bond between two carbon atoms. The general formula for alkynes is \(C_nH_{2n-2}\). The presence of a triple bond makes alkynes even more reactive than alkenes.
  
  Example:
  Ethyne \((\ce{C2H2})\), also known as acetylene, is a simple alkyne. It is used in welding due to its high-energy combustion reaction.

Characteristics of Unsaturated Compounds

• Double or Triple Bonds:
  The key feature of unsaturated compounds is the presence of double or triple bonds. These bonds are more reactive than single bonds and allow the molecule to undergo addition reactions, where atoms or groups of atoms are added to the molecule.
• Less Stable:
  Unsaturated compounds are generally less stable than saturated compounds. The double and triple bonds are more likely to react with other molecules.
• Physical Properties:
  Unsaturated hydrocarbons often have lower melting and boiling points compared to their saturated counterparts. Many unsaturated compounds are liquids at room temperature and may have a pungent or distinct odor.

Reactivity

Unsaturated compounds are more chemically reactive due to the presence of double or triple bonds. These compounds readily participate in addition reactions where atoms or molecules can add across the double or triple bonds. For example, in the presence of hydrogen, alkenes and alkynes undergo hydrogenation (adding hydrogen across the double or triple bond) to form saturated compounds.

One of the most fundamental ways that carbon atoms bond is by forming chains. In this structure, carbon atoms are connected to each other in a linear sequence through single covalent bonds. These chains can vary in length and can also be straight or have bends depending on how the carbon atoms bond with each other.

Types of Carbon Chains

• Straight Chains:
  These are linear arrangements of carbon atoms. In straight chains, each carbon atom is bonded to its neighbouring carbon atom with a single bond, forming a continuous, unbroken line. For example, butane \((\ce{C4H10})\) is a straight-chain alkane, with four carbon atoms connected by single bonds.
  \[\scriptsize \begin{array}{ccccccc} & & \ce{H} & & \ce{H} & &\ce{H}&&\ce{H} \\ & & |&&|&&|&&| \\ \ce{H}&-&\ce{C} & - & \ce{C} & - & \ce{C} & - & \ce{C}&-&\ce{H} \\ & & |&&|&&|&&| \\ & & \ce{H} & & \ce{H} & & \ce{H}&& \ce{H} \\ & & & & & & \end{array} \]
• Branched Chains:
  When one or more carbon atoms in the chain are attached to additional carbon atoms, the chain becomes branched. Branched chains increase the complexity of the molecule and often influence its properties. For example, isobutane \((\ce{C4H10})\) is a branched version of butane, where the carbon atoms are arranged differently but still contain the same number of atoms.

  

Carbon Rings

Another unique and important structural arrangement that carbon atoms can form is rings. Carbon atoms can bond with each other to form closed loop structures. This type of bonding is especially significant in the chemistry of organic compounds, particularly in cyclic compounds like aromatic compounds and heterocyclic compounds.

Types of Carbon Rings

• Aromatic Rings:
  Aromatic compounds are cyclic hydrocarbons that have alternating single and double bonds between carbon atoms in the ring. These compounds are highly stable due to the resonance of the electrons within the ring. A classic example is benzene (C₆H₆), which consists of six carbon atoms arranged in a hexagonal ring with alternating single and double bonds.

  

• Aliphatic Rings:
  These are cyclic compounds without alternating double and single bonds. For example, cyclohexane (C₆H₁₂) is a six-membered ring with single bonds between all carbon atoms. Unlike aromatic rings, aliphatic rings are typically less stable but still play a significant role in organic chemistry.
• Heterocyclic Rings:
  In these rings, carbon atoms are bonded with other elements, such as oxygen, nitrogen, or sulfur, as part of the ring structure. These heterocyclic compounds are important in biology and medicine. For example, pyridine (C₅H₅N) is a nitrogen-containing heterocyclic compound.

A functional group is a set of atoms bonded in a specific arrangement that replaces one or more hydrogen atoms in a hydrocarbon. While the rest of the molecule may remain unchanged, the functional group determines the compound’s physical and chemical properties, its reactivity, and even its smell and boiling point.

For example, replacing a hydrogen atom in ethane (C₂H₆) with an –OH group results in ethanol (C₂H₅OH), which behaves completely differently from ethane. This drastic change in behavior happens because the functional group (–OH) introduces new chemical abilities into the molecule.

Importance of Functional Groups

• They define the family or class of an organic compound.
• They decide how a compound will react during chemical reactions.
• They help chemists predict properties such as acidity, solubility, and boiling point.
• They allow easy identification and classification of organic compounds.

Common Functional Groups in Class X Syllabus

• Alcohols – The Hydroxyl Group (–OH):
  Alcohols contain the –OH group attached to a carbon atom.
  • Example: Ethanol (C₂H₅OH)
  • Properties: Alcohols often dissolve in water, burn with a clean flame, and react with sodium to release hydrogen gas.
• Aldehydes – The Aldehyde Group (–CHO):
  Aldehydes have a carbon atom double-bonded to an oxygen atom and single-bonded to a hydrogen atom (–CHO).
  • Example: Ethanal (CH₃CHO)
  • Properties: Usually have sharp smells and are used in perfumes and preservatives.
• Ketones – The Carbonyl Group (C=O):
  Ketones contain a carbonyl group (C=O) bonded between two carbon atoms.
  • Example: Propanone (CH₃COCH₃), commonly known as acetone
  • Properties: Good solvents and used in nail polish removers and industry.
• Carboxylic Acids – The Carboxyl Group (–COOH):
  Carboxylic acids contain the –COOH group.
  • Example: Ethanoic acid (CH₃COOH)
  • Properties: Sour in taste, acidic in nature, react with bases to form salts and water.
• Halides – The Halogen Group (–X):
  In halides, one hydrogen atom is replaced by a halogen like chlorine, bromine, fluorine, or iodine.
  • Example: Chloroethane (C₂H₅Cl)
  • Properties: Often used in industrial reactions and solvents.

A homologous series is a group of organic compounds in which:

• All members have the same functional group.
• Each successive member differs by a –CH₂– (methylene) unit.
• They follow a general molecular formula.
• They show a gradual variation in properties like boiling point, melting point, and smell.

Characteristics of a Homologous Series

• All members have the same functional group.
• Each successive member differs by a –CH₂– unit.
• They follow a general molecular formula (e.g., alkanes: \(C_nH_{2n+2}\)).
• Show gradual changes in physical properties like boiling and melting points.
• Have similar chemical properties due to the same functional group.
• Can be prepared by similar chemical methods.
• Members show a regular increase in molecular mass.

nomenclature of carbon compounds refers to the systematic method used to name organic molecules. Naming becomes essential because carbon compounds can form long chains, branches, and functional groups, leading to thousands of possible structures. To avoid confusion, scientists follow rules set by the International Union of Pure and Applied Chemistry (IUPAC).

Below is a simple and clear explanation suitable for NCERT Class 10 level.

1. Identify the Longest Carbon Chain
   • Choose the longest continuous chain of carbon atoms.
   • This chain determines the parent name(Root Name).

   No. of Carbon	Root Name
   1	Meth
   2	Eth
   3	Prop
   4	But
   5	Pent
   6	Hex
   7	Hept
   8	Oct
   9	Non
   10	Dec

2. Check for Saturation or Unsaturation

   Bond Type	Primary Suffix
   Single Bond	ane
   Double Bond	ene
   Triple Bond	yne

3. Identify and Locate Functional Groups

   Suffix

   Functional Group	Secondary Suffix
   -OH (Alcohol)	-ol
   -CHO (Aldehyde)	-al
   -C=O (Ketone)	-one
   -COOH (Caboxylic acid)	-oic acid
   -NH (Amines)	-amine

   Prefix

   Functional Group	Prefix
   \(\ce{-CH3}\)	Methyl
   \(\ce{-C2H5}\)	Ethyl
   \(\ce{-COOH}\)	Carboxy
   \(\ce{-OH}\)	Hydroxy
   \(\ce{-Cl}\)	Chloro
   \(\ce{-Br}\)	Bromo

4. Number the Carbon Chain
   • Number from the side that gives the functional group OR double/triple bond the lowest number.
   • For branches or substituents, include the number of the carbon they are attached to.
5. Identify Branches (Substituents)
   • Extra carbon groups attached to the main chain are named as: \(\ce{CH3 → }\) Methyl
     \(\ce{C2H5 → }\) Ethyl

Method

Position of Substituents/ Prefix/ Root Word/ Position of Double or Triple Bond/ Primary Prefix/ Position of Fn Grp/ Secondary Suffix

Rules

1. Identify longest Carbon chain
2. Lowest Number Rule
   • Numbering is done in such a way that branched Carbon atoms/ Substituent Carbon atoms get the lowest possible number
   • If the chain contains some multiple bond then the Carbon atom which are involved in the multiple bond should get lowest possible number
3. Using prefixes Di, Tri etc
   • If more than one similar alkyl group is present are in the compound then their position is denoted separately and prefixes like Di, Tri, Tetra etc is attached to the name of substitents. The positions of the attached substituents are separated by commas
4. Arrangement of Prefixes should be in alphabetical order
   • In a compound if different Alkyl substituents is present then their name is written in alphabetical order. For such compounds numerical prefixes like Di, Tri, Tetra etc are not considered for the alphabetical order
5. Numbering of different alkyl substituents at the equivalent position
   • If the compound contains two alkyl substituents at the equivalent position then numbering of the parent chain is done in such a way that the alkyl substituent which come first in the alphabetical order gets the lowest number
6. The longest chain of Cabon containing the functional group is numbered in such a way that the functional group is attached the carbon atom processing lowest possible numbering the chain
7. If the name of the functional group is to be given as a suffix, and the suffix of the functional group begins with a vowel a, e, i, o, u, then the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix. For example, a three-carbon chain with a ketone group would be named in the following manner – Propane – ‘e’ = propan + ‘one’ = propanone.

PRIORITY IN NUMBERING

1. Functional Group (Carboxylic, Ketone, Alcohol)
2. Multiple Bond (Triple, Double)
   • In case double and triple Bond both present then -ene would be given priority over -yne as suffix
   • \[\scriptsize \begin{array}{cccccccc} \color{red}{1}&&\color{red}{2}&&\color{red}{3}&&\color{red}{4}&&\color{red}{5}\\ \ce{HC&#&C&-&CH&=&C&-&CH3} \end{array} \] \[\text{pent-3-en-1-yne}\] \[\text{not pent-3-yne-1-ene}\]
   • \[\scriptsize \begin{array}{cccccccc} \color{red}{1}&&\color{red}{2}&&\color{red}{3}&&\color{red}{4}&&\color{red}{5}\\ \ce{H2C&=&C&-&CH2&-&C&#&CH} \end{array} \] \[\text{pent-1-en-4-yne}\] \[\text{not pent-4-ene-1-yne}\]