3.1: Lewis Electron-Dot Diagrams The bonding between atoms in a molecule can be topically modeled though Lewis electron dot diagrams. Creating Lewis diagrams is rather simple and requires only a few steps and some accounting of the valence electrons on each atom. Valence electrons are represented as dots. When two electrons are paired (lone pairs), they are represented by two adjacent dots located on an atom, and when two paired electrons are shared between atoms (bonds), they are shown as lines. 3.1.1: Resonance 3.1.2: Breaking the octet rule with higher electron counts (hypervalent atoms) 3.1.3: Formal Charge 3.1.4: Lewis Fails to Predict Unusual Cases - Boron and Beryllium 3.2: Valence Shell Electron-Pair Repulsion The Valence Shell Electron Repulsion (VSEPR) model can predict the structure of most molecules and polyatomic ions in which the central atom is a nonmetal; it also works for some structures in which the central atom is a metal. VSEPR builds on Lewis electron dot structures and together can predict the geometry of each atom in a molecule. The main idea of VSEPR theory is that pairs of electrons (in bonds and in lone pairs) repel each other. 3.2.1: Lone Pair Repulsion 3.2.2: Multiple Bonds 3.3: Valence Bond Theory - Hybridization of Atomic Orbitals The geometrical shape and the inherent physical/chemical properties seen in molecules can be attributed to atomic and molecular orbitals. Features of molecular structure can be explained by taking into consideration (1) how orbitals interact within a single atom to form hybrid atomic orbitals and (2) how atomic orbitals between different atoms interact, giving rise to molecular orbitals. This module will serve as a reminder of the fundamental concepts of bonding as they relate to molecular struc 3.4: Molecular Orbital Theory Molecular Orbital (MO) Theory is a sophisticated bonding model. It is generally considered to be more powerful than Lewis and Valence Bond Theories for predicting molecular properties, however this power comes at the price of complexity. In its full development, MO Theory requires complex mathematics, though the ideas behind it are simple. Atomic orbitals (AOs) that are localized on individual atoms combine to make molecular orbitals (MOs) that are distributed over the molecule. 3.4.1: Formation of Molecular Orbitals from Atomic Orbitals 3.4.2: Molecular Orbitals from s Orbitals 3.4.3: Molecular Orbitals from p Orbitals 3.4.4: Molecular orbitals from d orbitals 3.4.5: Nonbonding Orbitals and Other Factors 3.4.6: Features of Molecular Orbital Diagrams 3.4.7: Diatomic Molecules of the First and Second Periods 3.4.8: Molecular Orbitals of Heteronuclear Diatomic Molecules 3.4.9: Ionic Compounds and Molecular Orbitals