University:
University of Arizona
Course:
CHEM 141 | General Chemistry Lecture I
Academic year:

2022
Views:

176

Pages:

2
Author:

folclord7m

Molecular Geometry 🌐 Molecules spread out their atoms as far away from each other as possible. In a two-dimensional world, the furthest apart that the four chlorine atoms can get is 90 degrees. However, in a three-dimensional world, each of these chlorine atoms can actually spread out further than 90 degrees, resulting in a 109.5 angle between each chlorine atom. This shape is called a tetrahedron. Three Simple Geometries 📐 Number of Things Geometry Bond Angle 2 Linear 180° 3 Trigonal Planar 120° 4 Tetrahedral 109.5° Hybridization 🔬 Hybridization is a change that atoms undergo to form bonds. Electron Geometry Bond Angle Hybridization Domains 2 180° sp 2 3 120° sp² 3 4 109.5° sp³ 4 Condensed Formulas 📝 A condensed formula is one that can be written on one line of type. Examples CH₃CH₂CH₂CH₂CH₃ CH₃(CH₂)₄CH₃ CH₃COCH₃ Sigma (σ) and Pi (π) Bonds 🔗 Single covalent bonds = one σ bond Double bonds = one σ bond + one π bond Triple bonds = one σ bond and two π bonds Examples Molecule Bond Lengths and Strengths Sigma (σ) Bonds Pi (π) Bonds 14 0 10 1 9 2 📊 Triple bonds are shorter and stronger than double bonds, which are shorter and stronger than single bonds. Orbital Combinations 🌀 sp³ orbitals: one 2s orbital and three 2p orbitals sp² orbitals: one 2s orbital and two 2p orbitals sp orbitals: one 2s orbital and one 2p orbital Resonance Structures 🔄 Resonance structures are different forms of a molecule that have the same arrangement of atoms but different arrangements of electrons. Rules for Drawing Resonance Structures Only electrons move, specifically pi electrons, lone pair electrons, or negative charges. Do not move atoms. You can move electrons toward or into an atom that does not have a full octet. If an atom already has a full octet, you can move electrons into it only if you push electrons out the opposite side. Cycloalkanes and Ring Strain ⭕️ Cycloalkanes are alkanes that are cyclic, or ringed. The ideal geometry of a carbon atom with four single bonds is tetrahedral, with a bond angle of 109.5°. Ring Strain Polygon Sum of Interior Angles Triangle 180° Square 360° Pentagon 540° Hexagon 720° Cyclohexane 🌀 Cyclohexane rings are very special because they are found in many real-life organic compounds. Cyclohexane is the most stable cycloalkane because it allows a near-perfect 109.5° bond angle. Chair Conformations Chair conformations are the most stable form of cyclohexane. Axial positions are less favorable than equatorial positions for larger groups due to 1,3-diaxial interactions. Axial vs. Equatorial Equatorial positions are more favorable than axial positions for larger groups. The most stable form of a cyclohexane ring will be the one that places the largest number of its appendages in the equatorial positions. Trans vs. Cis Cyclohexanes 🔀 If two substituents are going in the same direction (both up or both down), they are cis to each other. If two substituents are going in opposite directions (one up and one down), they are trans to each other.