Covalent bonding is a type of chemical bonding where atoms share electrons with each other. Unlike ionic bonds, where electrons are transferred from one atom to another, covalent bonds involve the sharing of electrons.
A covalent bond is formed when two atoms share one or more pairs of electrons. This sharing allows each atom to attain a stable electron configuration, typically resembling that of a noble gas.
Formation of Covalent Bonds
1.Single Covalent Bond: When two atoms share one pair of electrons, a single covalent bond is formed. For example, in hydrogen gas (H2), two hydrogen atoms share one pair of electrons.
\[
\text{H} \cdot + \cdot \text{H} \rightarrow \text{H} - \text{H}
\]
2. Double Covalent Bond: When two atoms share two pairs of electrons, a double covalent bond is formed. For example, in oxygen gas (O2), two oxygen atoms share two pairs of electrons.
\[
\text{O} :: + :: \text{O} \rightarrow \text{O} = \text{O}
\]
3.Triple Covalent Bond: When two atoms share three pairs of electrons, a triple covalent bond is formed. For example, in nitrogen gas (N2), two nitrogen atoms share three pairs of electrons.
\[
\text{N} ::: + ::: \text{N} \rightarrow \text{N} \equiv \text{N}
\]
Characteristics of Covalent Bonds
Directionality: Covalent bonds have specific orientations in space, leading to definite shapes for molecules.
Strength: Covalent bonds are generally strong, requiring significant energy to break.
Electrical Conductivity: Covalently bonded substances are usually poor conductors of electricity.
Solubility: Covalent compounds are often soluble in nonpolar solvents but insoluble in water.
Melting and Boiling Points: Covalent compounds typically have lower melting and boiling points compared to ionic compounds.
Carbon: The Building Block of Life
Carbon is a unique element in the periodic table, known for its ability to form a wide variety of compounds.
It has an atomic number of 6, with four electrons in its outermost shell.
Covalent Bond in Carbon
1.Tetravalency of Carbon
Carbon has four valence electrons, which means it can form four covalent bonds with other atoms. This tetravalency leads to a vast array of compounds.
2. Formation of Single, Double, and Triple Bonds
Single Bond: Carbon can form a single bond with other carbon atoms or different elements by sharing one pair of electrons. Example: Methane ($CH_4$).
Double Bond: Carbon can form a double bond by sharing two pairs of electrons. Example: Ethene ($C_2H_4$).
Triple Bond: Carbon can form a triple bond by sharing three pairs of electrons. Example: Ethyne (C₂H₂).
3.Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. These compounds may have long chains of carbon,
branched chains of carbon or even carbon atoms arranged in rings.
Straight Chains: Carbon atoms can form long straight chains, as in propane ($C_3H_8$).
Branched Chains: Carbon atoms can form branched structures, as in isobutane.
Rings: Carbon atoms can form ring structures, as in cyclohexane.
Saturated and Unsaturated Carbon Compounds
Carbon compounds that single bonds between carbon atoms are known as saturated carbon compounds. These compounds are normally not very reactive
Carbon compounds that contain double or triple bonds between carbon atoms are known as unsaturated carbon compounds. These compounds are more reactive than saturated carbon compounds, which contain only single bonds.
Chains, Branches, and Rings
Carbon compounds can form various structures, including straight chains, branched chains, and rings. Examples include methane, ethane, propane, and others, containing 1, 2, 3, or more carbon atoms in chains. Chains
Carbon atoms can form straight chains by connecting to each other through single bonds. Examples
Branches
In addition to forming straight chains, carbon atoms can also form branched structures. Example
IsoButane
Rings
Some carbon compounds have carbon atoms arranged in the form of a ring. Example
Cyclohexane, which has the formula $C_6H_{12}$ and a ring structure.
Benzene ($C_6H_6$), another ring-structured compound.
Structural Isomers
Carbon's ability to form covalent bonds leads to structural isomers, compounds with the same molecular formula but different structures. For example, butane ($C_4H_{10}$) has two different possible structures.
Hydrocarbons
Carbon compounds containing only carbon and hydrogen are called hydrocarbons. These include:
Alkanes: Saturated hydrocarbons with single bonds.
Alkenes: Unsaturated hydrocarbons with one or more double bonds.
Alkynes: Unsaturated hydrocarbons with one or more triple bonds.
Functional Group
A hydrogen atom in Hydrocarbon can be replaced with another atom or group such that valency is satisfied.The another atom is called hetroatom
These heteroatoms and the group containing these confer specific properties to the compound, regardless of the length and nature of the carbon chain are called functional groups.
Homologous series
A homologous series is a series of organic compounds having the same functional group and general formula but differing by a constant unit, usually a $CH_2$ group.
Members of a homologous series exhibit a gradual change in physical properties, such as boiling point and melting point, while retaining similar chemical properties.
Characteristics of a Homologous Series
Same Functional Group: All members of a homologous series contain the same functional group, which determines their chemical properties.
General Formula: Members of a homologous series can be represented by a general formula. For example, the general formula for alkanes is CₙH₍₂ₙ₊₂₎.
Difference of CH₂ Group: Consecutive members of a homologous series differ by a CH₂ group. This difference leads to a gradual change in physical properties.
Gradual Change in Physical Properties: As the molecular weight increases in the series, physical properties such as boiling point and melting point gradually change.
Similar Chemical Properties: Due to the presence of the same functional group, members of a homologous series exhibit similar chemical reactions.
Examples
Alkanes: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), etc.
Alkenes: Ethene (C₂H₄), Propene (C₃H₆), Butene (C₄H₈), etc.
Alcohols: Methanol (CH₃OH), Ethanol (C₂H₅OH), Propanol (C₃H₇OH), etc.
Nomenclature
The names of compounds in a homologous series are based on the name of the basic carbon chain modified by a “prefix” “phrase before” or “suffix”
“phrase after” indicating the nature of the functional group.
Naming a carbon compound can be done by the following method –
(i) Identify the number of carbon atoms in the compound. A compound having three carbon atoms would have the name propane.
(ii) In case a functional group is present, it is indicated in the name of the compound with either a prefix or a suffix
(iii) 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.
(iv) If the carbon chain is unsaturated, then the final ‘ane’ in the name of the carbon chain is substituted by ‘ene’ or ‘yne’
This can be summarized as
Chemical Properties of Carbon Compounds
Carbon compounds exhibit a wide range of chemical properties due to the diverse structures and functional groups they can contain. The document specifically highlights the following aspects:
1. Combustion
Most carbon compounds, particularly hydrocarbons, undergo combustion in the presence of oxygen. This reaction produces carbon dioxide, water, and energy in the form of heat and light.
$C + O_2 -> CO_2 + heat + light$
$CH_4 + O_2 -> CO_2 + H_2O heat + light$
3. Oxidation
Carbon compounds can be oxidized to form various products. For example, alcohols can be oxidized to form aldehydes, ketones, or carboxylic acids, depending on the specific conditions and the nature of the alcohol.
$CH_3CH_2OH\xrightarrow[\text{(Acidified) } K_2Cr_2O_7 + heat]{\text{(alkaline)} KMnO_4 + heat}CH_3COOH$
4. Addition Reactions
Unsaturated carbon compounds, such as alkenes and alkynes, can undergo addition reactions. In these reactions, atoms or groups are added to the carbon atoms involved in the double or triple bond, converting them to single bonds. For example, hydrogen can be added to an alkene in a hydrogenation reaction.
Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons
5. Substitution Reactions
Saturated carbon compounds, such as alkanes, can undergo substitution reactions. In these reactions, one atom or group is replaced by another. For example, a hydrogen atom in methane can be replaced by a chlorine atom in the presence of chlorine gas and light.
$CH_4+ Cl_2 -> CH_3Cl + HCl$ (in the presence of sunlight)
Properties of Ethanol
Ethanol, also known as ethyl alcohol, is a widely used compound with various applications, from industrial uses to consumption in alcoholic beverages. Here's a detailed look at the properties of ethanol:
Physical properties are as below
Chemical Properties of Ethanol
1. Combustion: Ethanol burns in oxygen to form carbon dioxide and water, releasing energy.
\[
C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O
\]
2. Oxidation: Ethanol can be oxidized to form acetaldehyde and further to acetic acid.
3. Esterification:Ethanol reacts with carboxylic acids to form esters, often used in fragrances and flavors.
4. Dehydration: In the presence of a strong acid, ethanol can be dehydrated to form ethene.
\[
C_2H_5OH \rightarrow C_2H_4 + H_2O
\]
5.Reaction with Sodium: Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas.
\[
2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2
\]
6. Acid-Base Behavior: Ethanol can act as a weak acid, donating a proton from the hydroxyl group, or as a weak base, accepting a proton. Biological Properties
1. Psychoactive Effects: Ethanol is the active ingredient in alcoholic beverages and has psychoactive effects on the human body.
2. Toxicity: While consumed in beverages, ethanol is toxic in large quantities and can lead to alcohol poisoning.Intake of even a small quantity of pure
ethanol (called absolute alcohol) can be lethal.
3. Antiseptic Qualities: Ethanol is used as a disinfectant and antiseptic in medical applications.
Properties of Ethanoic acid
Ethanoic acid, commonly known as acetic acid, is a prominent member of the carboxylic acid family and is the main component of vinegar.
Physical properites are
Chemical Properties of Ethanoic Acid
1. Acidic Nature: Ethanoic acid is a weak acid that dissociates in water to form acetate ions and hydronium ions.
\[
CH_3COOH \rightleftharpoons CH_3COO^- + H_3O^+
\]
2. Esterification: Ethanoic acid reacts with alcohols to form esters, often used in fragrances and flavors.
\[
CH_3COOH + C_2H_5OH \rightarrow CH_3COOC_2H_5 + H_2O
\]
3.Reaction with Bases: Ethanoic acid reacts with bases to form acetate salts. For example, with sodium hydroxide, it forms sodium acetate.
\[
CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O
\]
4. Oxidation and Reduction: Being a carboxylic acid, ethanoic acid is relatively resistant to oxidation. However, it can be reduced to ethanol using reducing agents. Biological Properties
1. Preservative Qualities: Ethanoic acid is used as a preservative in the food industry due to its antibacterial properties.
2. Toxicity: Concentrated ethanoic acid can be corrosive and should be handled with care. Industrial Applications
1. Manufacture of Chemicals: Ethanoic acid is used in the synthesis of various chemicals, including acetic anhydride and acetate esters.
2. Textile Industry: Used in the dyeing and finishing of textiles.
3. Food Industry: As a key component of vinegar, it's used for flavoring and preservation.
