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topics 1 - L TOPIC 1 STRUCTURE AND BONDING(Chapter 1 These...

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CHEM 2311 B Topic 1 slide 2 TOPIC 1. STRUCTURE AND BONDING (Chapter 1) These packages of notes are designed for use in conjunction with CHEM 2311 lectures. If you miss a lecture, get the completed notes from another student. Reading assignments (from Solomons) are given in the top right corner ( S:#-# ), along with relevant problems from the end of the chapter . L CHEM 2311 B Topic 1 slide 3 OBJECTIVES 1. Introduction to organic chemistry and review of terms 1. Describe distribution of electrons in organic molecules (atomic electronic configurations, Lewis structures, resonance) 2. Describe bonding C-C and C-H bonds in organic molecules (hybridization, overlap of atomic orbitals). 3. Describe molecular geometry.
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CHEM 2311 B Topic 1 slide 4 SOME BASIC STRUCTURAL FEATURES Empirical Formula - Ratio of atoms in a compound. Molecular Formula - Number of each atom in a molecule. Valency - Elements form a fixed number of bonds (H 1, O 2, N 3, C 4). Structure - Arrangement of atoms and bonds in a molecule. Isomers - Different compounds with the same molecular formula. Constitutional isomers - Compounds with the same formula, but with different connectivity of atoms. S:1.3 CHEM 2311 B Topic 1 slide 5 A VERY GOOD PLACE TO START: ELECTRONIC CONFIGURATION OF ATOMS H 1s 1 He 1s 2 Li 1s 2 , 2s 1 Be 1s 2 , 2s 2 B 1s 2 , 2s 2 ,2p 1 1s 2 , 2s 2 ,2p x 1 C 1s 2 , 2s 2 ,2p 2 1s 2 , 2s 2 ,2p x 1 2p y 1 N 1s 2 , 2s 2 ,2p 3 1s 2 , 2s 2 ,2p x 1 2p y 1 2p z 1 O 1s 2 , 2s 2 ,2p 4 1s 2 , 2s 2 ,2p x 2 2p y 1 2p z 1 F 1s 2 , 2s 2 ,2p 5 1s 2 , 2s 2 ,2p x 2 2p y 2 2p z 1 Ne 1s 2 , 2s 2 ,2p 6 1s 2 , 2s 2 ,2p x 2 2p y 2 2p z 2 Core Electrons vs Valence Electrons Carbon: 2 core electrons & 4 valence electrons
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BONDING: LEWIS STRUCTURES AND FORMAL CHARGES The Octet Rule Atoms exchange or share electrons to complete the valence shell (adopt Noble gas electronic configuration) Ionic Bonds Atoms exchange electrons to form ions which are electrostatically attracted to one another. Li + F Li + F Ionic bonds are typically formed between atoms which are highly electronegative and highly electropositive Prob: 1.17-19 He Ne Ar S:1.4-1.7 CHEM 2311 B Topic 1 slide 7 Ionic bonds are typically formed between atoms which are highly electronegative and highly electropositive
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CHEM 2311 B Topic 1 slide 8 Covalent Bonds (Lewis Structures) Atoms share valence shell electrons to form covalent bonds F + F F F N H H H Recommendation: ALWAYS explicitly show lone pairs of electrons C H H H H O H H CHEM 2311 B Topic 1 slide 9 “Exceptions” to the Octet “Rule” Octet rule is the tendency to have eight valence electrons - only applies strictly to second row elements F B F F O S O OH HO S:1.6
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CHEM 2311 B Topic 1 slide 10 Formal Charge Formal Charge = Number of valence electrons minus (# lone pair electron + ½ number of bonding electrons) H H B H H H H N H H H H O H H H C H H S:1.7 CHEM 2311 B Topic 1 slide 11 Some Common Valencies B C B C C N N N O O O F F Not:
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CHEM 2311 B Topic 1 slide 12 Nitrogen (5 valence electrons) Carbon (4 valence electrons) CHEM 2311 B Topic 1 slide 13 Constitutional Isomers Given the common valencies of atoms (C=4, H=1), there might be a number of possible arrangements.
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