CLASS- 10 SCIENCE (Medium- English)

 

CHPATER- 4 CARBON AND ITS COMPOUNDS

NOTES

1. Carbon is a versatile element. All living structures are carbon-based.

2. Ionic compounds have high melting and boiling points and conduct electricity in solution or molten state.

3. Most carbon compounds are not good conductors of electricity.

4. The atomic number of carbon is 6.

5. Elements that form ionic compounds achieve stability by gaining or losing electrons from their outermost shell. Carbon has four electrons in its outermost shell and needs to gain or lose four electrons to attain a noble gas configuration.

A) Carbon can gain four electrons to form a C⁴⁻ anion, but holding four extra electrons would be difficult for a nucleus with only six protons.

B) Carbon can lose four electrons to form a C⁴⁺ cation, but losing four electrons would leave only two electrons with a nucleus of six protons, requiring an extremely high amount of energy to form a stable carbon cation.

6. Many elements, like carbon, also form molecules by sharing electrons. The shared electrons belong to the outermost shell of both atoms, allowing them to achieve a stable noble gas configuration.

7. Each hydrogen atom attains the electronic configuration of its nearest noble gas, helium, which has two electrons in its K shell.

• The shared pair of electrons between two hydrogen atoms forms a single covalent bond.

8. Double bond– In an oxygen molecule (O₂), each oxygen atom shares two electrons, forming two shared electron pairs. This is called a double bond between the two atoms.

9. Triple Bond– The atomic number of nitrogen is 7. To achieve an octet configuration, each nitrogen atom in an N₂ molecule shares three electrons, forming three shared electron pairs. This results in a triple bond between the two nitrogen atoms.

10. Methane– Methane is a carbon compound widely used as a fuel. It is the main component of biogas and compressed natural gas (CNG). It is one of the simplest carbon compounds, with the chemical formula CH₄.

11. Covalent Bond– A bond formed between two atoms by sharing a pair of electrons is called a covalent bond.

• In covalent bond molecules, the intramolecular bonds are strong, but the intermolecular forces are weak.

• These compounds have low boiling and melting points due to weak intermolecular forces.

• Due to the nature of covalent bonding, carbon has the ability to form a large number of compounds.

12. Two Key Factors of Carbon- 

A) Carbon has a unique ability to form bonds with other carbon atoms, leading to the formation of large molecules. This property is called Catenation.

• Saturated Compounds– Carbon compounds in which carbon atoms are connected only by single bonds are called saturated compounds.

• Unsaturated Compounds– Carbon compounds that contain double or triple bonds between carbon atoms are called unsaturated compounds.

• The extent of catenation found in carbon compounds is not observed in any other element.

B) Carbon has a valency of four allowing it to form bonds with four other carbon atoms or with other monovalent elements.

13. Saturated and Unsaturated Compounds-

• To obtain the structure of simple carbon compounds, carbon atoms are first linked together by single bonds. Then, hydrogen atoms are added to satisfy the remaining valency of carbon. Example: Ethane (C₂H₆)

Each carbon atom has three unsatisfied valencies, so each carbon forms bonds with three hydrogen atoms to fulfill its valency.

• All atoms satisfy their valency through single bonds in these compounds. Such compounds are called saturated compounds. They are less reactive.

Ethene- C₂H₄

Carbon atoms bonded by a single bond

One valency of each carbon atom remains unsatisfied. This can only be satisfied when there is a double bond between two carbon atoms.

• Carbon compounds that have double or triple bonds between carbon atoms are called unsaturated carbon compounds, and they are more reactive compared to saturated carbon compounds.

• Compounds that have the same molecular formula but different structures are called structural isomers.

14. Carbon is a highly versatile element. In a hydrocarbon chain, it replaces one or more hydrogen atoms in such a way that its valency remains satisfied. The elements that replace hydrogen in such compounds are called heteroatoms.

• Heteroatoms and the functional groups in which they are present impart specific properties to compounds. These properties do not depend on the length or nature of the carbon chain; hence, they are called functional groups.

15. Homologous Series– A series of compounds in which the hydrogen atom in the carbon chain is replaced by the same type of functional group is called a homologous series.

• When the molecular mass increases in a homologous series, a gradual variation in physical properties is observed.

• The solubility, as a physical property, also shows a similar trend in a particular solvent. However, the chemical properties, which are fully determined by the functional group, remain consistent within a homologous series.

16. Nomenclature of Carbon Compounds– In a homologous series, the names of the compounds are based on the basic carbon chains, which are modified by prefixes or suffixes according to the nature of the functional group.

The method by which the naming of a carbon compound can be done-

A) To determine the number of carbon atoms in a compound, identify the carbon chain. A compound with three carbon atoms will be named propane.

B) The presence of the functional group is indicated in the compound's name with a prefix or suffix, depending on its position and nature.

C) If the name of the functional group is to be given based on a suffix and the name of the functional group begins with a vowel (a, e, i, o, u), then the last 'e' from the carbon chain name is dropped, and the appropriate suffix is added to modify the name.

D) In an unsaturated carbon chain, the final "ane" in the name of the carbon chain is replaced with "ene" or "yne," depending on whether there is a double or triple bond, respectively.

17. Chemical properties of carbon compounds-

a) Combustion– In all its allotropes, carbon burns in oxygen to produce carbon dioxide along with heat and light. During combustion, most carbon compounds also release a significant amount of heat and light.

C + O₂ → CO₂ + heat and light

b) Oxidation– Some substances have the ability to give oxygen to other substances. These substances are called oxidizing agents.

• Alkaline potassium permanganate or acidified potassium dichromate oxidize alcohols into acids, meaning they add oxygen to the starting substance.

c) Addition Reaction– In the presence of catalysts like palladium or nickel, unsaturated hydrocarbons add hydrogen to form saturated hydrocarbons. Catalysts are substances that cause a reaction to proceed at a different rate without being consumed or altered in the reaction. The hydrogenation of vegetable oils is typically carried out using nickel as a catalyst in this type of reaction.

d) Substitution Reaction– In the presence of sunlight, a very fast reaction occurs in which chlorine gets added to the hydrocarbon. Chlorine replaces the hydrogen atoms one by one. This type of reaction is called a substitution reaction.

18. Ethanol and acetic acid-

Properties of Ethanol– Ethanol is in a liquid state at room temperature. It is called alcohol and is an important component of all alcoholic beverages. It is also a good solvent.

• It is used in medicines such as tincture of iodine, cough syrup, tonic, etc.

Reactions of ethanol-

a) Reaction with sodium-

2Na+2CH3​CH2​OH→2CH3​CH2​O−Na++H2

Alcohol reacts with sodium to release hydrogen gas. In the reaction with ethanol, the second product formed is sodium ethoxide.

b) Reaction to form unsaturated hydrocarbons– When ethanol is heated with concentrated sulfuric acid at 443K, dehydration of ethanol occurs, resulting in the formation of ethene.

CH3​CH2​OH→CH2​=CH2​+H2​O

In this reaction, sulfuric acid acts as a dehydrating agent, which removes water from ethanol.

Properties of Acetic Acid– Acetic acid is commonly known as vinegar and is related to the carboxylic acid group.

• A 3-4% solution of acetic acid is called vinegar, and it is used as a preservative in pickles.

• The melting point of pure acetic acid is 290K, and therefore, in cold climates during the winter, it freezes. For this reason, it is called glacial acetic acid.

Reactions of acetic acid-

a) Esterification Reaction– Esters are primarily formed by the reaction of an acid and an alcohol. Acetic acid reacts with pure ethanol in the presence of an acid catalyst to form an ester.

CH3​COOH+CH3​CH2​OH⇌CH3​COOCH2​CH3​+H2​O

• By reacting with sodium hydroxide, which is a base, an ester is converted back into an alcohol and the sodium salt of the carboxylic acid. This reaction is called saponification.

• CH3​COOC2​H5​+NaOH→C2​H5​OH+CH3​COONa

b) Reaction with a base– Like mineral acids, acetic acid reacts with a base such as sodium hydroxide to form a salt and water.

NaOH+CH3​COOH→CH3​COO−Na++H2​O

c) Reaction with carbonate and bicarbonate- Acetic acid reacts with carbonate and bicarbonate to produce salt, carbon dioxide, and water. The salt formed in this reaction is called sodium acetate.

2CH3​COOH+Na2​CO3​→2CH3​COONa+H2​O+CO2

​

CH3​COOH+NaHCO3​→CH3​COONa+H2​O+CO2​ 

19. Soap and Detergent-

• Soap molecules are sodium and potassium salts of long-chain fatty acids. The ionic part of soap interacts with water, while the carbon chain interacts with oil.

• Soap molecules have two ends with different properties. The end that is soluble in water is called the hydrophilic end, and the other end, which is soluble in hydrocarbons, is called the  hydrophobic end.