Chem 333 1st Edition Lecture 2Outline of Last Lecture I. Atomic StructureII. ElectronsIII. Octet Rule Outline of Current Lecture IV. Bondsa. Polarb. Ionicc. Covalentd. Doublee. TripleV. Bond anglesVI. ResonanceCurrent LectureI. BondsA. Polar bondsi. when elements do not share electrons equallyii. Ex.) H_2_OB. Ionic bondsi. when electrons transfer fully C. Covalent bondsi. Sharing of electronsD. Formal charge = valence electrons – number of electrons in lone pairs – ½shared electronsi. x.) NH_3_ H-N-H Formal charge = 5 – 2 – 3 = 0 HE. Multiple bondsi. Double bonds1. share 4 electrons or 2 pairs2. ex. CH_2_CH_2_VII. Bond Anglesa. VSPERi. Valence shell electron pair repulsionii. Valence electrons repel each other (like repels like) therefore electrons want to be as far apart as possibleiii. Look for regions of electron density1. Lone pair2. Single bond3. Double bond4. Triple bondiv. 4 regions of electron density1. 109.5 degree bond angle2. Tetrahedral 3. Ex.) CH_4_ and H_2_ov. 3 regions of electron density1. 120 degree bond angle2. Trigonal planar3. ex.) CH_2_Ovi. 2 regions of electron density1. 180 degree bond angle2. linear3. ex.) C_2_H_2_VIII. Resonancea. Resonance structuresi. More than 1 way to draw a moleculeii. When drawing arrows1. The tail is the electron sourcea. Where electrons are coming from2. The tail is the electron sinka. Where electrons are going3. Double headed arrow means two electrons are moving4.iii. Rules1. All structures have the same number of electrons2. All structures must be valid lewis structures3. NEVER move atoms – only move electrons4. Number of paired and unpaired electrons must remain the same iv. Relative importance1. Not all resonance structures contribute equallya. Filled valence shell (octet) contribute moreb. Maximum number of covalent bonds contribute mirec. The resonance structure with the least separation of unlike charges is more favorabled. Negative charge on the most electronegative atom is the most favorable **image from google