CHEM 1211 Lecture 21 Outline of Last Lecture I Covalent Bonds A N2 B CO32II Octet Rule Violators A BCl3 B I3Outline of Current Lecture I Clicker Questions A Clicker Question 1 B Clicker Question 2 C Clicker Question 3 II Bond Length Strength III Bond Strength IV Strengths of Covalent Bonds V Using Bond Dissociation Enthalpies VI Valence Bond Theory A VB Theory Analysis of BeCl2 Current Lecture I Clicker Questions A Clicker Question 1 What is the electron pair geometry for CIF3 A Linear B Trigonal Planar C Tetrahedral D Trigonal Bipyramidal E Octahedral B Clicker Question 2 What is the molecular geometry A Seesaw B T Shaped II III IV V VI C Square Planar D Linear E Bent C Clicker Question 3 Is it polar A Yes B No Bond Length Strength Bond order is proportional to two important bond properties 1 Bond Strength 2 Bond Length Bond Strength Bond Bond Dissociation Enthalpy kj mol H H 436 C C 346 C C 602 C TRIPLE BOND C 835 N TRIPLE BOND N 945 The greater number of bond order the higher the bond strength and the shorter the bond Strengths of Covalent Bonds Energy required to break covalent bonds is called the bond dissociation enthalpy D Using Bond Dissociation Enthalpies Estimate the energy of the reaction H H g Cl Cl g 2 H Cl g Net energy H energy required to break bonds energy evolved when bonds are made H H 436 KJ mol x 1 mol 436 KJ Cl Cl 242 KJ mol x 1 mol 242 KJ H Cl 432 KJ mol x 2 mol 864 KJ H 186 KJ mol Valence Bond Theory Covalent bonds are formed when atomic orbitals overlap Hybridization atomic orbitals on central atom mix combine to form hybrid orbitals AO in hybrid orbitals out Resulting orbitals bond to other atoms in the molecule Total B Lone Pairs on Central Electron Pair Geometry Hybridization Bond Angles Atom 2 3 4 5 6 Linear Trigonal planar Tetrahedral Trigonal bipyrimidal Octahedral A VB Theory Analysis of BeCl2 2s 2p E 2s 2p excited state Be 3s 3p Cl Cl3p Sp Sp2 Sp3 Sp3d 180 120 109 5 90 120 180 Sp3d2 90 180 sp Hybridization 2sp hybrid orbitals
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