CHEM 1211 Lecture 21Outline of Last Lecture I. Covalent BondsA. N2B. CO32-II. Octet Rule ViolatorsA. BCl3B. I3-Outline of Current Lecture I. Clicker QuestionsA. Clicker Question #1B. Clicker Question #2C. Clicker Question #3II. Bond Length/StrengthIII. Bond StrengthIV. Strengths of Covalent BondsV. Using Bond Dissociation EnthalpiesVI. Valence Bond TheoryA. VB Theory Analysis of BeCl2Current Lecture: I. Clicker QuestionsA. Clicker Question #1What is the electron pair geometry for CIF3?A. LinearB. Trigonal PlanarC. TetrahedralD. Trigonal BipyramidalE. OctahedralB. Clicker Question #2What is the molecular geometry?A. SeesawB. T ShapedC. Square PlanarD. LinearE. Bent C. Clicker Question #3Is it polar?A. YesB. NoII. Bond Length/Strength- Bond order is proportional to two important bond properties1. Bond Strength2. Bond LengthIII. Bond StrengthBond Bond Dissociation Enthalpy (kj/mol)H – H 436C – C 346C = C 602C (TRIPLE BOND) C 835N (TRIPLE BOND) N 945- The greater number of bond order, the higher the bond strength and the shorter the bond. IV. Strengths of Covalent Bonds- Energy required to break covalent bonds is called the bond dissociation enthalpy, D.V. 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 KJCl – Cl = 242 KJ/mol x 1 mol = 242 KJH – Cl = -(432 KJ/mol x 2 mol) = -864 KJ H = -186 KJ/molVI. 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 GeometryHybridization Bond AnglesAtom2 Linear Sp 180°3 Trigonal planar Sp2120°4 Tetrahedral Sp3109.5°5 Trigonal bipyrimidalSp3d 90°, 120°, 180°6 Octahedral Sp3d290°, 180°A. VB Theory Analysis of BeCl2 2s 2p +E 2s 2p (excited state) sp Hybridization: 2sp hybrid orbitalsBe 3s 3pCl
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