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UMass Amherst CHEM 261 - Atomic Bonding and Hybrid Orbital Introduction

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CHEM 261 1st Edition Lecture 2Outline of Last Lecture:I. Outline Syllabus II. What is Organic ChemistryIII. Atomic StructureOutline of Current Lecture:I. Atomic BondingII. Chemical Bonding Theory: Valence Bond TheoryIII. Bond TrendsIV. Hybrid Orbitals V. Structural RepresentationAtomic Bonding:-Atoms form bonds because the compound that results is more stable than the separate atomsAchieving Atomic Happiness via sharing electrons:1. Lewis dot Structures:-“Electron dot structures”-Valence shell electrons of an atom are represented as dotsEx. Carbon would have 4 dots (2s 2p) to represent its outer shell valence electrons2. Kekule (line) structures-2 electron covalent bonds represented as a line, rather than as dots, drawn between atoms**both concepts are also applicable to both double and triple bonds**The “octet rule”: elements tend to combine in such a way as to fill the outer most valence shells so that they contain 8 electrons, or a noble gas electron configuration (very stable). This can be done by forming…-ionic bonds: electrostatic interaction in which electrons are completely transferred between atoms-covalent bonds: shared electron bond, forms a molecule. Can be polar (unequal sharing) or nonpolar (equal sharing)Valence Bond Theory:-Bonds form when 2 atoms get close to each other AND one singly occupied orbital on one atom overlaps with a single occupied orbital on another. The electrons are now paired in overlapping orbitals and are attracted to the nuclei of both atoms, which bonds the atoms together. Ex. H2 molecule, the H-H bond results from the overlapping of the two singly occupied hydrogen1s orbitalsBond Trends:-refer to table 1.2 in ebook** as bond strength increases, bond length decreasesHybridization:Sp3 orbital: Formed by combining an s orbital with 3 p orbitals. The overlapping orbitals allow for stronger bonds than un-hybridized s and p orbitals. Sp3 are tetrahedral in shape** the “3” in sp3 refers to how many of each type of orbital combine-NOT how many electrons occupy it**sp3 orbitals can be found with anything that makes 4 bonds, can include lone electron pairsExample from class…. Sp2 orbital: formed by combining an s orbital with 2 p orbitals. Can create a bent shape**sp2 orbitals can be found with anything that makes 3 bonds, can include lone electron pairs, for example, double bonds!Example from class:Sp: 2 sp orbitals combine, create a linear shape. Triple bonds!!**sp orbitals can be found with anything that makes 2 bonds, can include lone electron pairs, for example, triple bonds!Sigma bonds: bonds formed by the head-on overlap of 2 orbitals along a line drawn between the nucleiStructural


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