General Chemistry CHEM 111 Getting to noble gas electron configurations through covalent bonds Chapter 8 Bonding and Molecular Structures 1 Chemical Bonds Filling Electron Shells We see ions form from ionic bonding in which electrons are transferred The addition by subtraction model for nonmetal metal combinations We now will focus on covalent bonding in which electrons are shared The win win outcome for nonmetals lending one electron each to a pair Nonmetals mutually gain one electron per covalent bond in their valence shells 2 Ionic Bond Addition by subtraction generates stable octets within the resulting valence shells 3 Covalent Bond Between Non Metals Notice that the electronic position is shown in the middle rather than to one side Note that covalent means corresponding or shared valence shells with electrons 4 Covalent Bond Sandwiches Shells Together Notice how the valence shells are conjoined in a covalent bond 5 Electronegativity Tugging at Shared Pair 6 Lewis Dot Structures How dotted electrons are arranged around elemental symbol nuclei Each dot represents one electron Elemental symbols represent the nuclei anchoring the electrons e Group 1 e G r o u p 3 e G r o u p 2 e Group 4 7 Bonding vs Lone Pair 8 Octet Rule Make a noble gas in terms of valence electron number Get to 8 Now you know why the HClBrIF elements make diatomic molecules 9 Drawing Lewis Structure Key Rule Just give the elements the bonds that they want Ex 3 Win Win Each F Group 7A wants one bond and P Group 5A wants three 10 Drawing Lewis Structure Key Rule Just give the elements the bonds that they want Ex 2 Win Win Each O Group 6A wants two bonds and C Group 4A wants four 11 Drawing Lewis Structure Key Rule Just give the elements the bonds that they want Ex 2 Tension Breeds Compromise Each O wants 2 bonds but S wants 2 total 12 Drawing Lewis Structure Key Rule Just give the elements the bonds that they want Ex meaning an H bonded to C on 1 side and an N bonded to C on the other Win Win Win H Group 1A wants 1 bond N wants 3 C wants 4 total 13 Drawing Lewis Structure Key Rule Just give the elements the bonds that they want Ex 2 ion meaning that the formal charge of needs to be assigned to 1 atom Win Win Each O wants 2 bonds while N takes the formal charge with 4 bonds 14 Drawing Lewis Structure Key Rule Just give the elements the bonds that they want Ex ion meaning that the formal charge of needs to be assigned to 1 atom Win Win H wants 1 bond while O takes the formal charge with 1 bond 15 Drawing Lewis Structure Key Rule Just give the elements the bonds that they want Ex ion meaning that the formal charge of needs to be assigned to 1 atom Win Win N wants 3 bonds while C takes the formal charge with 3 bonds 16 Exceptions to Octet Rule Any element whose block touches the base of the d 17 Exceptions to Octet Rule 18 19 Exceptions to Octet Rule Anything with fewer than 4 valence electrons 20 Exceptions to Octet Rule 21 22 Formal Charge FC When the number of lone electrons isn t Something must have happened to the electrons they were gained lost Formal charge assigns this gain loss within a covalently bonded compound We assign a formal charge to each atom in a compound ion 23 Formal Charge FC Formal charges sum up to zero for molecules and the charge for ions Watch for when the number of lone electrons doesn t reflect the bonds lent 24 Using FC to Select the Best Lewis Structure Keep the formal charges as small as possible Give the electronegative atoms the negative formal charges These statements are principles rather than rules because you can t always Get what you want Rule of Least Preposterousness 25 26 Using FC to Select the Best Lewis Structure If you love plugging and chugging into formulas use this for FC 27 28 Resonance Different spatial arrangement of electron pairs rather than atoms 29 Resonance 30 Resonance 31 Resonance 32 33 About That Geometry VSEPR Theory 34 Central Atom 3 Bond Groups Geometry 35 36 37 38 39 Electronegativity and Covalent Bond Poles 40 Bond Polarity 41 From Bond Polarity to Molecular Polarity Dipole Moment Corresponds to Polarity 42 Molecular Polarity 43 44 From Poles to Pure Electric Forces stands for 1 Multiplied Ionic Charges 2 Inverse Square Distance Between Nuclei 45 Bond Length Distance Between Nuclei 46 Bond Order 47 Bond Order Resonance Structures 48 Bond Length Trends with Radius and Order 49 Bond Dissociation Energy Bond Enthalpy 50 Bond Energies in 51 Bond Order Bond Length Bond Energy 52 Consider cost of breaking reactant bonds and gain from forming product bonds Enthalpy of Reaction rH Note the use of the summation symbol in this mathematical equation This equation is chemistry s version of a cost benefit analysis for a reaction reaction s cost reaction s benefit 53 Enthalpy of Reaction 54 Calculating Enthalpy of Reaction 55
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