Chemical Bonding CHEM 1315 - 002
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This 3 page Class Notes was uploaded by Julia Tang on Sunday October 25, 2015. The Class Notes belongs to CHEM 1315 - 002 at University of Oklahoma taught by Fares Z Najar in Fall 2015. Since its upload, it has received 15 views. For similar materials see General Chemistry in Chemistry at University of Oklahoma.
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Date Created: 10/25/15
Chemical Bonds Unit 5 o Examines the relationship between electronic structure chemical bonding forces and chemical bond type Ionic o Electrostatic attraction between ions metals nonmetals O eg table salt lattice structure Covalent bond 0 Attractions between electrons and nuclei 0 Repulsions between electrons o Repulsions between nuclei Metals 0 Electron sea model Electrons are not localized to individual atoms Hence that are delocalized and shared equally between all atoms in lattice O Atoms in a sea of electrons Ready to be given away Electronegativity EN 0 EN is the ability of an atom in a molecule to attract electrons to itself same pattern as electron affinity O Florine the most EN 0 Delta EN predict the bonding nature of two atoms 0 EN larger ENsmaler 0 Small 004 covalent Clz 39 Electrons shared equally nonpolar 0 Intermediate 0402 polar covalent HCI I Shared unequally polar 0 Large 20 ionic NaCl I Electrons transferred 0 EN and Bond Polarity 0 Difference in EN between two atoms use to gauge the polarity of the bond between them 0 Dipole moment is a measurement for polarity 0 Unit D coulombs meter cm 0 Dipole is a material with pos and neg end and is O Directly prop to size of the partial charge amp Distance between them 0 In general the more electrons two atoms share and the larger the atoms are the larger the dipole moment 0 There is a diff between a molecule having polar bonds and molecule being polar A molecule can possess polar bonds between the central atoms And the bonded atoms yet overall the molecule can be Nonpolar 0 The arrangement of polar bonds around the central atom Determines if the molecule is polar O The bonded atoms are arranged symmetrically and the bonded atoms are identical or have similar electronegativity s o Ionic bonds strong lattice energy 0 Attraction assemble into a solid array called a lattice or crystalline lattice O Na 6 Cl around and vice versa 0 Lattice energy 0 Magnitude depends i Charge of the ions ii Size of the ions iii Arrangement of ions 0 Ion size and lattice energy 0 Magnitude of lattice energy decreases with increasing size due to the ions not being able to get as close to each other 0 Going down column the lattice energy lessens size matters nuclei and the charges 0 Larger charge stronger attraction ion charge is more important Lewis symbols use the chemical symbol for element plus a dot for each valence electron o All the noble gases will have saturated Octet rule gain lose or share electrons until they are surrounded by eight valence electrons Duet rule for elements where the octet rule is not possible ie He Li Be2 Covalent bonds may be represented visually by Lewis structures Electron pairs shared between atoms are represented by drawing a line between the atoms and unpaired electrons are shown as dots Electron pairs shared between two atoms are bonding electrons or bonding pair 0 H lsl HH 0 CI Ne3s23p5 ClC Drawing Lewis structures Sum the valance electrons from al atoms Write the sums for the atoms to show how atoms are attached and connect them with a single bond 0 Central atoms must be the least electronegative except for hydrogen Complete the octet rule except for hydrogen Place any leftover electrons on the central atom even if this yields more than 8 electrons Formal Charge Formal charge the number of valence electrons in An isolated atom minus the number of electrons Assigned to the atom in the Lewis structure To calculate formal charges on any atom in a Lewis Structure 0 All unshared nonbonding electrons are assigned to the atom on which they are found 0 For any bond single double or triple half of the bonding electrons are assigned to each atom in the bond 0 Subtracting the number of electrons assigned to the atom from the number of valence electrons that an atom has to determine formal charge How to determine the best 0 The sum of all formal charges in a neutral atom must be zero if the molecule is not an ion 0 The sum of all formal charges in an ion must be equal Resonance structure Resonance structures must have the same connectivity only electron positions can change
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