Alkanes: Properties, Naming, and Uses of Saturated Hydrocarbons - Prof. Anjum, Slides of Organic Chemistry

Download Alkanes: Properties, Naming, and Uses of Saturated Hydrocarbons - Prof. Anjum and more Slides Organic Chemistry in PDF only on Docsity! ee Nee we) tb ee ALKANES Prepared by: Ramisa Anjum Department of Pharmacy UAT A= eo AoC: Mee Celie HOMOLOGOUS SERIES ¢ There are millions of different organic compounds and chemists have devised a method of classifying them into families with similar formulae and properties. ¢ Each family of organic compounds is called a homologous series. * Ahomologous series is a family of compounds with the same general formula, same functional group and similar chemical properties. HOMOLOGOUS SERIES CHARACTERISTICS Organic compounds in the same homologous series have the following characteristics: Same general formula Same functional group Similar chemical properties but varying in reactivity Physical properties varv gradually along the series FUNCTIONAL GROUPS AND GENERAL FORMULA ¢ A functional group is an atom or group of atoms that gives a compound its characteristic chemical properties. ¢ Organic compounds in the same homologous series have similar chemical properties due to the same functional group. ¢ Each member of the series differs from the next by a —-CH,- unit. GENERAL FORMULA OF ALKANES? H methane | H-C CH, NTT Molecular Formula metiane Ale ethane propane butane pentane Hi heptane brig eee ely Ethene Molecular formula Propene Butene Alkane CH, methane CH, CH, ethane CH, CH, CH, propane methane Alcohol CH..OH methanol CH, CH, OH ethanol CH, CH, CH, OH propanol methanol Carboxylic acid Alkene HCO,H methanoic acid CH,CO,H CH. CH, ethanoic acid ethene CH,CH, CO,H CH, CH CH, propanoic acid propene SG BE mere acid ethene WHAT ARE ALKANES? ¢ Alkanes are a homologous series of saturated hydrocarbons that contain only carbon- carbon single covalent bonds. ¢ In an alkane molecule, all the outer electrons of each carbon are used in forming single covalent bonds with four other atoms, hence, alkanes are said to be saturated. ¢ Alkanes have the general formula C,,H,,,.5 (where n 2 1) HOW ARE ALKANES No. of C atoms Molecular formula Structural formula methane CH, CH, propane CH3CH2CH3 CH3CH,CH,CH3 PHYSICAL PROPERTIES OF ALKANES ¢ Physical states Ci to C4 C5 to C17 C18 onwards Liquid Physical state at room temperature Butane blowlamp Kerosene lamp Bitumen used in road surfacing PHYSICAL PROPERTIES OF ALKANES ¢ As the number of carbon atoms in the molecules increases, they become less viscous (flow less easily). ¢ This is due to the stronger intermolecular forces of attraction and ¢ Larger molecules get tangled eel STE RIWA PHYSICAL PROPERTIES OF ALKANES ¢ As the number of carbon atoms in the molecules increases, their densities also increase. Liquid alkanes have densities less than 1g/cm? and they float on water. Density (g/cm*) PHYSICAL PROPERTIES OF ALKANES ¢ As the number of carbon atoms in the molecules increases, they become less flammable (more difficult to burn). ¢ The larger alkane molecules contain a higher percentage of carbon and this makes it more difficult to burn. * The larger alkanes also tend to produce a smokier flame due to incomplete combustion of the alkane molecules. CHEMICAL PROPERTIES OF ALKANES Combustion Alkane + oxygen > carbon dioxide + water vapour CH, (g) + 202 (9) CO (g) + 2H20 (g) ; A = -890kJ/mol The reaction is highly exothermic and a large amount of heat energy is released. This is why alkanes make good fuels. CHEMICAL PROPERTIES OF ALKANES ¢ Substitution Reactions ¢ A substitution reaction is one in which an atom or group of atoms replace other atoms ina molecule. ¢ It is usually a slow reaction that is difficult to control and a mixture of products is usually obtained. CHEMICAL PROPERTIES OF ALKANES ¢ Reaction is initiated by ultra-violet light which provides the energy to break the covalent bond in the chlorine molecule to produce chlorine atoms. q-co MY, oc chlorine molecule chlorine atoms