CBSE Class 10 Science Notes Chapter 4 Carbon and its Compounds:, Summaries of Family and Consumer Science

Download CBSE Class 10 Science Notes Chapter 4 Carbon and its Compounds: and more Summaries Family and Consumer Science in PDF only on Docsity! Class 10 Science Notes Chapter 4 Carbon and its Compounds Chemical substances containing carbon are referred to as carbon compounds. Except for hydrogen, there are more carbon compounds than any other chemical element. Compounds of carbon with double bonds and triple bonds are called unsaturated compounds while those with carbon-carbon single bonds are called saturated compounds. Covalent Bonding The difficulty of Carbon Form a Stable Ion To achieve the electronic configuration of the nearest noble gas,, if the carbon atom loses four of its valence electrons, a huge amount of energy is involved. C4+ ion hence formed will be highly unstable due to the presence of six protons and two electrons. If the carbon atom gains four electrons to achieve the nearest electronic configuration of the noble gas, Ne, C4− ion will be formed. But again, a huge amount of energy is required. Moreover, in C4+ ions it is difficult for 6 protons to hold 10 electrons. Hence, to satisfy its tetravalency, carbon shares all four of its valence electrons and forms covalent bonds. Ionic Bond Ionic bonding involves the transfer of valence electron/s, primarily between a metal and a nonmetal. The electrostatic attractions between the oppositely charged ions hold the compound together. Ionic compounds: 1. Are usually crystalline solids (made of ions) 2. Have high melting and boiling points 3. Conduct electricity when melted 4. They are mostly soluble in water and polar solvents Covalent Bond A covalent bond is formed when pairs of electrons are shared between two atoms. It is primarily formed between two same nonmetallic atoms or between nonmetallic atoms with similar electronegativity. Lewis Dot Structure Lewis structures are also known as Lewis dot structures or electron dot structures. These are basically diagrams with the element’s symbol in the center. The dots around it represent the valence electrons of the element. Lewis structures of elements with atomic numbers 5-8 Covalent Bonding in H2, N2 and O2 Formation of a single bond in a hydrogen molecule: Each hydrogen atom has a single electron in the valence shell. It requires one more to acquire the nearest noble gas configuration (He). Therefore, both atoms share one electron each and form a single bond. Formation of a double bond in an oxygen molecule: Each oxygen atom has six electrons in the valence shell (2, 6). It requires two electrons to acquire the nearest noble gas configuration (Ne). Therefore, both atoms share two electrons each and form a double bond. ● Water has two lone pairs. ● The two O-H covalent bonds are polar in nature. ● The o atom is more electronegative than the H atom. Thus, the shared pair of electrons lies more toward the O atom. ● This causes the O atom to acquire a slightly negative charge and the H atom a slightly positive charge. ● Covalent Bonding in Carbon A methane molecule (CH4) is formed when four electrons of carbon are shared with four hydrogen atoms as shown below. Friendly Carbon Why Carbon Can Form so Many Compounds Catenation occurs most readily with carbon due to its small size, electronic configuration, and unique strength of carbon-carbon bonds. Tetravalency, catenation, and the tendency to form multiple bonds with other atoms account for the formation of innumerable carbon compounds. Catenation Catenation is the self-linking property of an element by which an atom forms covalent bonds with the other atoms of the same element to form straight or branched chains and rings of different sizes. It is shown by carbon, sulfur, and silicon. S8 In its native state, sulfur show catenation of up to 8 atoms in the form of an S8 molecule. It has a puckered ring structure. Versatile Nature of Carbon Tetravalency, and Catenation The fact that carbon can form single, double, and triple bonds demonstrates its versatility. It can also form chains, branching chains, and rings when joined to other carbon atoms. Hydrogen, oxygen, carbon, and a few additional elements make up organic molecules. Organic compounds, on the other hand, are significantly more numerous than inorganic compounds that do not form bonds. Carbon is a chemical element with the atomic number 6 and the symbol C. It’s a versatile element that can be found in a wide variety of chemical combinations. Carbon’s versatility is best appreciated through properties like tetravalency and catenation. ● Tetravalency: Carbon has a valency of four so it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element. ● Catenation: The property of a carbon elements due to which its atom can join one another to form long carbon chains is called catenation. Mp, Bp, and Electrical Conductivity Covalent compounds: 1. Are molecular compounds 2. Are gases, liquids, or solids 3. Have weak intermolecular forces 4. Have low melting and boiling points 5. Are poor electrical conductors in all phases 6. Are mostly soluble in nonpolar liquids Allotropes of Carbon – The phenomenon of the existence of the same element in different physical forms with similar chemical properties is known as allotropy. – Some elements like carbon, sulfur, phosphorus, etc., exhibit this phenomenon. – Crystalline allotropes of carbon include diamond, graphite, and, fullerene. – Amorphous allotropes of carbon include coal, coke, charcoal, lamp black, and gas carbon. Diamond Diamond has a regular tetrahedral geometry. This is because each carbon is connected to four neighboring carbon atoms via single covalent bonds, resulting in a single unit of a crystal. These crystal units lie in different planes and are connected to each other, resulting in a rigid three-dimensional cubic pattern of the diamond. Diamond: The isomers that differ in the structural arrangement of atoms in their molecules are called structural isomers and the phenomenon is known as structural isomerism. Benzene Benzene is the simplest organic, aromatic hydrocarbon. Physical properties: colorless liquid, pungent odor, flammable, volatile. Structure: Cyclic in nature with chemical formula, C6H6, i.e., each carbon atom in benzene is arranged in a six-membered ring and is bonded to only one hydrogen atom. It includes 3 double bonds which are separated by a single bond. Hence, this arrangement is recognized to have conjugated double bonds and two stable resonance structures exist for the ring. functional Groups and Nomenclature Functional Groups An atom or a group of atoms which when present in a compound gives specific physical and chemical properties to it regardless of the length and nature of the carbon chain is called a functional group. Classification of Functional Groups Main Functional Groups: (i) Hydroxyl group (-OH): All organic compounds containing the -OH group are known as alcohols. For example, Methanol (CH3OH), Ethanol (CH3−CH2−OH), etc. (ii) Aldehyde group (-CHO): All organic compounds containing the -CHO group are known as aldehydes. For example, Methanal (HCHO), Ethanal (CH3CHO), etc. (iii) Ketone group (-C=O): All organic compounds containing the (-C=O) group flanked by two alkyl groups are known as ketones. For example, Propanone (CH3COCH3), Butanone (CH3COCH2CH3), etc. (iv) Carboxyl group (-COOH): All organic acids contain a carboxyl group (-COOH). Hence, they are also called carboxylic acids. For example, Ethanoic acid (CH3COOH), Propanoic acid (CH3CH2COOH), etc. (v) Halogen group (F, CI, Br, I): The alkanes in which one or more than one hydrogen atom is substituted by X (F, CI, Br, or I) are known as haloalkanes. For example, Chloromethane (CH3Cl), Bromomethane (CH3Br), etc. Homologous Series Homologous series constitutes organic compounds with the same general formula, and similar chemical characteristics but different physical properties. The adjacent members differ in their molecular formula by −CH2. Examples of homologous series Methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is CnH2n+2. Methane (CH4), Ethane (CH3CH3), Propane (CH3CH2CH3), and Butane (CH3CH2CH2CH3). It can be noticed that there is a difference of −CH2 unit between each successive compound. Nomenclature of Carbon Compounds The International Union of Pure and Applied Chemistry (IUPAC) decided on some rules to name carbon compounds. This was done to maintain uniformity throughout the world. Names that are given on this basis are popularly known as IUPAC names. Physical Properties The members of any particular family have almost identical chemical properties due to the same functional group. Their physical properties such as melting point, boiling point, density, etc., show a regular gradation with the increase in molecular mass. Chemical Properties A chemical property is a property that describes a substance’s ability to undergo a specific chemical change. We look for a chemical shift to identify a chemical attribute. A chemical change always results in the formation of one or more types of matter that are distinct from the matter that existed before to the change. Combustion Reactions Combustion means the burning of carbon or carbon-containing compounds in the presence of air or oxygen to produce carbon dioxide, heat, and light. 2CH3OH + 3O2→ 4H2O + 2CO2 For example, Naphthalene also undergoes combustion in the presence of oxygen to afford carbon dioxide gas and water. The chemical equation for this reaction is given: 12O2 + C10H8→ 4H2O + 10CO2 Flame Characteristics Saturated hydrocarbons give a clean flame while unsaturated hydrocarbons give a smoky flame. In the presence of limited oxygen, even saturated hydrocarbons give smoky flame. A black substance formed by combustion or separated from fuel during combustion, rising in fine particles and adhering to the sides of the chimney or pipe conveying the smoke especially: the fine powder consisting chiefly of carbon that colors smoke called soot. Oxidation Oxidation is a chemical reaction that occurs in an atom or compound and results in the loss of one or more electrons. potassium hydroxide solution, hydrolysis of fat takes place; soap and glycerol are formed. This alkaline hydrolysis of oils and fats is commonly known as saponification. The reaction of Ethanoic Acid with Metals and Bases Ethanoic acid (Acetic acid) reacts with metals like sodium, zinc, and magnesium to liberate hydrogen gas. 2CH3COOH+2Na→2CH3COONa+H2(↑) It reacts with a solution of sodium hydroxide to form sodium ethanoate and water. CH3COOH+NaOH→CH3COONa+H2O The reaction of Ethanoic Acid with Carbonates and Bicarbonates Carboxylic acids react with carbonates and bicarbonates with the evolution of CO2 gas. For example, when ethanoic acid (acetic acid) reacts with sodium carbonate and sodium bicarbonate, CO2 gas is evolved. 2CH3COOH+Na2CO3→2CH3COONa+H2O+CO2 CH3COOH+NaHCO3→CH3COONa+H2O+CO2 Soaps and Detergents Cleansing Action of Soap When soap is added to water, the soap molecules uniquely orient themselves to form spherical shape micelles. The non-polar hydrophobic part or tail of the soap molecules attracts the dirt or oil part of the fabric, while the polar hydrophilic part or head,(−COO−Na+, remains attracted to water molecules. The agitation or scrubbing of the fabric helps the micelles to carry the oil or dirt particles and detach them from the fibers of the fabric. ’ Hard Water Hard water contains salts of calcium and magnesium, principally as bicarbonates, chlorides, and sulfates. When soap is added to hard water, calcium and magnesium ions of hard water react with soap forming insoluble curdy white precipitates of calcium and magnesium salts of fatty acids. 2C17H35COONa+MgCl2→ (C17H35COO)2Mg+2NaCl 2C17H35COONa+CaCl2→ (C17H35COO)2Ca+2NaCl These precipitates stick to the fabric being washed and hence, interfere with the cleaning ability of the soap. Therefore, a lot of soap is wasted if the water is hard. Frequently asked Questions on CBSE Class 10 Chemistry Notes Chapter 4: Carbon and its Compounds What is a micelle? Micelle is an aggregate of molecules in a colloidal solution (those formed in detergents). What are the types of covalent bonds? 1. Single covalent bond 2. Double covalent bond 3. Triple covalent bond