CHEM1920 Lecture 2 (Jan 2025) PDF

CHEM1920 Lecture 2 January 22, 2025 Topics from Course Outline 3 Molecules have certain shapes. These specific arrangements of atoms and electrons minimize repulsion and energy. sp3 sp2 sp...

CHEM1920 Lecture 2 January 22, 2025 Topics from Course Outline 3 Molecules have certain shapes. These specific arrangements of atoms and electrons minimize repulsion and energy. sp3 sp2 sp Counting atoms and lone pairs helps us remember shape 4 How does methane form 4 bonds? HYDROGEN S H -4 bonds of same energy C H -bonds formed by the pairing up of H 1s electrons from H and the 4 H valence electrons from C. Methane Inconsistency #1 (If 2s and 2p have different energies then how are all 4 bonds CARBO the same?) N 5 How does methane form 4 bonds? HYDROGEN S -4 bonds of same energy -bonds formed by the overlap of 1s H electrons from H and 2s and 2p C H electrons from C. H H Methane Inconsistency #2 (If each bond is formed by an atom contributing an unpaired electron then how are the 3rd and 4th bonds formed?) CARBO N 6 sp3 hybridization 1 orbital increased in E. But 3 orbitals decreased in E Overall lower E arrangement. 7 Hybridization helps to rationalize the arrangement of a molecule HYDROGEN S -4 bonds of same energy -bonds formed by the overlap of 1s H electrons from H and electrons from 4 equivalent orbitals in C. C H H sp3 H Methane 8 C3H8 HH H H sp3 + s C C C H overlap sp3 + sp3 overlap H H H 9 How does carbon form three sigma and one pi bond in ethene? HYDROGENS Have 3 half-filled or empty orbitals on carbon to make four bonds. 3 of similar energy 1 of higher energy. Once again hybridization is required. CARBO N 10 sp2 hybridization 1200 11 H H H H C C C C H H H H p + p overlap sp2 + sp2 overlap 12 sp hybridization 1800 13 H C C H H C C H p + p overlap sp + sp overlap 14 Video https://youtu.be/Kb0mxAMHnfE?si=joF30mkLG_IFQhHv&t=248 15 Hybridization: free rotation vs Fixed Bonds sp3 sp2 sp Limitation: does not convey size difference in sp3 vs sp2 vs sp 16 17 What is the hybridization? How do we know? 1. sp? 2. sp2? 3. sp3? 18 19 Hydrocarbons SATURATED UNSATURATED (all sigma (pi and sigma bonds) bonds) 20 Simple Oxygen and Halogen containing compounds 21 JSME Practice 22 Recap Counting charge clouds to determine hybridization Types of hybridization Using ballons visualize hybridization Drawing bond line structures Practice interpreting bond line structures and functional groups Naming