Chapter 8 Covalent Bonding 8.1 Molecular Compounds Diatomic Molecules Monatomic ex: He, Ne Salts and Formula Unit ‐ Ionic bonds ‐ What kind of elements? Melting points tend to be... Molecule‐neutral group of atoms ‐covalent bonds Jan 45:29 PM Covalent Bonds • Nonmetals with similar electronegativities • Electrons are shared • Form molecular compounds Jan 45:34 PM Properties of Molecular Compounds • lower MP and BP than ionic compounds • many are gases or liquids at room T • most made of two or more nonmetals Jan 45:39 PM What do Molecular Formulas tell us? Jan 49:45 PM Br2 KBr CH4 N 2 H2 Ne2 SO3 1. Do any of these NOT exist? 2. Are any ionic compounds? 3. Which formulas represent molecules? 4. How many atoms are in SO3? Jan 49:50 PM Jan 49:56 PM Single Covalent Bonds Octet Rule and Covalent Bonding... they still want to be like a Noble gas Jan 410:09 PM Jan 410:18 PM Unshaired Pair Structural Formulas Jan 410:20 PM Jan 410:26 PM Double and Triple Covalent Bonds Jan 410:57 PM Jan 411:02 PM Carbon Dioxide Draw electron dot structures for each molecule. Bromine Chlorine gas PCl3 H2O2 NF3 SBr2 Jan 56:28 PM Resonance Structures Jan 410:31 PM Bond Dissociation Energy ‐energy needed to break 1 mole of bonds O3 ‐high energy = strong covalent bond C C = 347 kj/mol When a molecule has two or more valid Lewis dot structures C C = C C Jan 56:51 PM 657 kj/mol = 908 kj/mol Jan 56:43 PM Coordinate Covalent Bonds C O C O Shared e‐ pair comes from one of the bonding atoms Jan 411:00 PM Jan 96:49 PM Table 8.2 Page 224 SO2 Coordinate covalent bond Exceptions to the Octet Electron pair donated by S NO2 Free Radicals BF3 Electron deficient Polyatomic Ions SO42‐ P and S can have expanded octets Jan 56:36 PM Jan 56:57 PM Molecular Orbitals Jan 57:19 PM Jan 57:20 PM VSEPR Theory Jan 57:24 PM Jan 57:11 PM Focus on regions of electron density http://intro.chem.okstate.edu/1314F00/Lecture/Chapter10/VSEPR.html Jan 57:12 PM Jan 1112:02 PM 8.4 Polar Bonds and Molecules Polar covalent Nonpolar covalent Jan 1112:03 PM Jan 168:10 PM Polar Molecules Bond Polarity Look at difference in electronegativity of atoms involved in bond (dipole) What you need to know.... 0‐0.4 = nonpolar Jan 1112:24 PM >1.7 = ionic Jan 1112:45 PM INTERmolecular vs. INTRAmolecular Forces INTERmolecular Forces ‐attraction between 2 or more molecules weaker than ionic or covalent bonds that join the atoms in molecules INTRAmolecular‐ Ionic Bond ‐BP is good measure of IMF ‐IMFs govern many physical properties like BP, MP, viscosity, surface tension Covalent Bond Metallic Bond What would happen if there were no IMFs? Feb 56:10 PM Feb 56:20 PM Dipole Dipole interactions ‐attraction between polar molecules (dipoles) 1. Van der Waals Forces Dispersion Forces ‐only IMF among Noble gas atoms and nonpolar molecules (resulting in their low BP) ‐force increases with mass Jan 1112:45 PM Feb 55:47 PM 2. Hydrogen Bonds ‐H bonded to strongly EN atom ‐Strongest of IMF ‐a temporary dipole moment is created Feb 55:47 PM Jan 168:28 PM H‐F H‐O H‐N Covalent Network Solids Jan 1112:24 PM Jan 1112:53 PM Jan 1112:52 PM
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