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1 2 Structure and Shape - Chapter 12 Valence Shell Electron Pair Repulsion (VSEPR) Theory In a real structure, the electron pairs will repel each other, distributing themselves in positions around the central atom so that they are as far away from each other as possible. This minimizes the potential energy of the molecule, something molecules like. 3 Molecular Geometry Bond Angle - the angle between two bonds formed by the same central atom. Table 12. 2 - summarize Examples: CO 2, H2O, NH3, H3O+, CO32-, NO3- 4 Geometry of Multiple Bonds The second and third electron pairs in double and triple bonds don’ don’t affect molecular geometry: Examples: BeF2, CO2, HCN BF 3, HCOH 5 Polarity of Molecules A polar molecule is one in which there is an uneven or unbalanced distribution of charge, resulting in + and - poles. We must know something about the bond angles and geometry before we can decide on polarity. Examples: CO 2, H2O NH 3, BF3, BF2H HCOH 6 Organic Chemistry Organic chemistry - the chemistry of carbon compounds. Hydrocarbons - compounds made up only of carbon and hydrogen. Alkanes - one type of hydrocarbon molecule which consist of carbon atoms attached to each other, forming chains. 7 Hydrocarbons Methane - CH 4 Ethane - C 2H6 (molecular formula) or CH 3CH3 (line formula) Propane - C 3H8 or CH3CH2CH3 Butane - C4H10 or CH3CH2CH2CH3 or CH3(CH2)2CH3 Pentane - C5H12 or CH3(CH2)3CH3 General Formula: CnH2n+2 8 Hydrocarbons isomers - molecules with the same molecular formula but different arrangements of atoms. Examples: pentane, 2-methylbutane 2- methylbutane,, 2,2-dimethylpropane 2,2-dimethylpropane Each isomer is different, having its own physical and chemical properties. - e.g. boiling points and melting points 9 Functional Groups Functional groups - groups of atoms that have chemical properties that depend on the molecular framework to which they are attached. Functional groups are important to organic chemistry because they affect how a molecule reacts. 10 Other Structures of Organic Compounds - Functional Groups 1) Alcohols - alkanes in which a hydrogen atom is replaced by a hydroxyl (OH) OH) group. - Example: ethanol, CH 3CH2OH. 2) Ethers - compounds that have two hydrocarbon groups bonded to an oxygen atom. - Example: diethyl ether, CH 3CH2OCH2CH3 11 Other Structures of Organic Compounds - Functional Groups 3) Carboxylic Acids - contain a carboxyl (COOH) COOH) group. - Example: acetic acid (vinegar), CH 3COOH 4) Esters - are similar to carboxylic acids, except that the hydrogen atom on the COOH group has been replaced by a group containing carbon. 12 Show aspirin structure. Show structures of codeine, morphine, and heroin. 13 Questions: You should be able to do the target check questions and examples throughout the chapter, as well as the end - of - chapter questions that begin on pg. 341. The blue numbered questions have answers provided at the end of the chapter. Other questions: #1 - 26, 30, 31, 33, 37