Organic Chemistry 1 Lecture (CHE 231) 8/27/20191.1Organic Chemistry oThe study of carbon-containing molecules and their reactions.oWe will be focusing on the electrons in the compoundsOrganic compounds contain carbon atoms, while inorganic compounds do not1.2Compounds with the same molecular formula but different structures are constitutional isomersAtoms that are most commonly bonded to carbon include N, O, H, and halides (F, Cl, Br, I).Each element generally forms a specific number of bonds with other atoms. 1.3 Covalent bondoA pair of electrons shared between two atoms oEx: What forces keep the bond at the optimal length?oAttractive forces between two differently charged nucleioRepulsive forces between the two positively charged nucleioRepulsive forces between the two negatively charged electronsYou can calculate the number of valence electrons by analyzing the e- configuration.Or for group A elements only, you can look at the group number on the periodic table. Group number= # of valence electrons. Lewis-Dot StructuresoDraw the individual atoms using dots to represent the valance electronsoPut the atoms together so they share pairs of electrons to fill out their octets.
oEx: NH3+++oNOTE: The nitrogen has a lone pair of electronsSimple Lewis StructuresoDraw the individual atoms using dots to represent the valance electrons.oPut the atoms together so they share pairs of electrons to make complete octets. 1.4 Atoms with an unbalanced or FORMAL chargeoAnion: Negatively chargedoCation: Positively ChargedAtoms in molecules are typically neutral but can also be ANIONIC or CATIONICTo determine formal chargeoCompare the number of valance electrons that it owns to the number of valance electrons that the atoms need to be neutral oEXAMPLE: Consider the formal charge on the atoms in the structure below, and determine if any of the atoms should have a formal chargeCarbon needs 4 valence electrons to be neutral (Group IV)Carbon is surrounded by 8 electrons here, but it only owns 4 of them (1 from each of the bonds).Since carbon owns 4 electrons, and needs 4 electrons to be neutral, it does not have a formal charge.Oxygen needs 6 valence electrons to be neutral (Group VI)Oxygen is surrounded by 8 electrons here, but it only owns 7 of them (1 from the bond, plus 3 lone pairs).Since oxygen owns 7 electrons here, and needs 6 electrons to be neutral, it has an extra electron, and therefore has a -1 charge.1.5
ElectronegativityoHow strongly an atom attracts shared electronsoEX:oF is the most electronegative atom You can remember the relative electronegativity of the atoms in the same column or row.Three types of BondsoCovalent Bond:Electrons shared between two atoms, where electronegativity difference is less than 0.5oPolar Covalent Bond:Electrons shared between the two atoms with electronegativity difference is between 0.5 and 0.7oIonic Bond:Electrons are not shared, the two atoms differ in electronegative by more than 1.7, and so the more electronegative atom owns the electrons. 4