Chapter 9 - Chapter 9: Chemical Bonds Chemical bond: force...

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Chapter 9: Chemical Bonds 1 Chemical bond: force that holds 2 atoms together Ionic bond: e- transferred from 1 atom to another. Covalent bond: e-s shared between 2 atoms Ionic Bonds What happens when a compound is formed by 1 atom with low E i (wants to lose e-) and 1 atom with large negative E ea (wants to gain e-)? Na + Cl Na + Cl → Na + + Cl - 1 s 2 2 s 2 2 p 6 3 s 1 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 1 s 2 2 s 2 2 p 6 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 loses e- gains e- + ion - ion In 3-D, this force of attraction yields 3-D array of ions. NaCl solid This arrangement of ions in 3-D is stable—stablized by Lattice Energy .
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Chapter 9: Chemical Bonds 2 Lattice Energy Na + ( g ) + Cl - ( g ) → NaCl( s ) - U = -787 kJ/mol The Covalent Bond H 2 molecule H atom 1p + 1e- repulsive forces: e- H1 : e- H2 p + H1 : p + H2 attractive forces e- H1 : p + H2 e- H2 : p + H1
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Chapter 9: Chemical Bonds 3 H 1 H 2 → H 1 H 2 molecule with covalent bond Can plot energy vs. internuclear distance Bond length = distance of H H bond Bond formation releases energy (graph: minimum is negative value) H + H → H H E = -436 kJ/mol H + H → H H + 436 kJ/mol Negative E means a release of energy. The reverse process—breaking a covalent bond— requires adding energy. H H → H + H D = +436 kJ/mol 436 kJ/mol + H H → H + H Bond Dissociation Energy, D, is 436 kJ/ml for H H. Polar Covalent Bonds Covalent bond – bond in which e-s are shared e-s shared equally: nonpolar covalent bond e-s shared unequally: polar covalent bond Cl 2 Cl Cl e-s shared equally Cl Cl bond is nonpolar
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Chapter 9: Chemical Bonds 4 HCl H Cl e-s shared unequally Cl wants e-s more than H wants e-s Cl more electronegative than H Electronegativity – ability of atom in covalent bond to attract shared e-s H Cl δ + δ - δ + : partial positive charge, results when e-s are pulled away from it δ - : partial negative charge, results when e-s are pulled toward it
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Chapter 9 - Chapter 9: Chemical Bonds Chemical bond: force...

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