sdf - Petrucci 10.1 Chemical Bonds Atoms interact to form...

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Unformatted text preview: Petrucci 10.1 Chemical Bonds Atoms interact to form molecules Molecule has lower energy than separated atoms Atoms are held together in molecule by bonds Ideal limits Ionic bond Electron(s) transferred from one atom to another resulting in ions with (pseudo) noble gas electron configurations Covalent bond Sharing of electrons leads to filled shell configurations for each atom in the molecule All bonds have some covalent character Ionic and Covalent Limit Ionic Bonds Na + Cl NaCl Na Cl [Na] + [ Cl ]- [Ne] 3 s 1 [Ne] 3 s 2 3 p 5 [Ne] [Ar] Covalent Bonds Cl + Cl Cl 2 Cl Cl Cl Cl Energy of Ionic Bond Na(g) + Cl(g)- NaCl(s) Step Energy Na (g)-- Na + (g) + e E 1 = I.E 1 (Na) = 496 kJ/mol Cl(g) + e -- Cl (g) E 2 = E.A. 1 (Cl) =- 349 kJ/mol Na(g) + Cl(g)-- Na + (g) + Cl (g) E 3 = E 1 + E 2 = +145 kJ/mol Positive energy means that E (Na + (g) + Cl- (g)) > E (Na(g) + Cl(g)) It costs energy to transfer electron Energy recovered when ions are brought together Na + (g) + Cl- (g)-- NaCl(s) Potential energy of two interacting charges is proportional to product of charges divided by separation distance Coulombs law V C = 1 4 q 1 q 2 r Permittivity of air: 8 . 854 10- 12 C 2 J 1 m 1 +1 cation: q 1 = +1 . 602 10- 19 C- 1 antion: q 2 =- 1 . 602 10- 19 C Na(g) + Cl(g)- NaCl(s) Step Energy Na(g) + Cl(g)-- Na + (g) + Cl (g) E 3 = +145 kJ/mol Na + (g) + Cl (g)-- Na + Cl (g) E C =- 503 kJ/mol r = 276 pm Na(g) + Cl(g)-- Na + Cl (g) E =- 358 kJ/mol The energy spent to form ions ( E 3 ) is more than recovered by Coulomb interaction ( E C ) when ions come together to form ion pair. As a result energy is released when the ionic solid is formed. More stable ionic compounds have Cation of element with low I.E. (METAL) Anion of element with large negative E.A (NON-METAL) 2 Petrucci 10.2 Covalent Bonds Covalent bonds are more difficult to describe Atomic orbitals overlap Two models that describe covalent bond- ing Valence-bond theory * Electrons are in localized bonds that arise from overlap of atomic orbitals Molecular orbital theory * Electrons occupy orbitals that are delocalized over entire molecule and made up of atomic orbitals Electrons tends to be shared so both atoms obtains a noble gas configuration Petrucci 10.8, 10.9 Bond Lengths and Bond Energies Bond order is the number of bonds between a pair of atoms Single covalent bond bond order one Double covalent bond bond order two Triple covalent bond bond order three The higher the bond order, the more electrons participate in the bond Higher bond order Shorter bond length Greater bond energy C- C C-- C CC...
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This note was uploaded on 12/04/2009 for the course CHE 15940 taught by Professor Madsen during the Spring '09 term at UC Davis.

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sdf - Petrucci 10.1 Chemical Bonds Atoms interact to form...

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