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Chapter 9: Chemical Bonds Chemical Terminology • Atom • Molecule Chemical Reactions • Formation and/or breaking of chemical bonds • Chemical energy • Chemical equation Fig 9.4 Valence Electrons and Ions • Outer orbital electrons participate in bonding • A-Group (family) number and electron dot notation • Octet rule Fig 9.5 Chemical Bonds • Attractive forces holding atoms together in compounds Three types of bonds: • Metallic • Ionic • Covalent Ionic Bonds • Chemical bond of electrostatic attraction • Example: NaCl – Na loses; Cl gains – No single NaCl molecule, per se. Common Ions and Polyatomic Ions Covalent Bonds Fig 9.8 Covalent Bonds • Covalent compound • Electron dot representation Multiple Covalent Bonds • Sharing of more than one electron pair • Examples – Ethylene: Double bond – Acetylene: Triple bond. Bond Polarity • Polar Covalent Bonds • Electronegativity Electronegativities Fig 9.10 Composition of Compounds • Common names • Modern approach - systematic sets of rules Ionic Compounds and Formulas Ionic Compound Names • Name of metal (positive) ion first; then non-metal (negative) ion • If no polyatomic ions are involved, the suffix –ide is added to the end of the non-metal • Many elements have variable charges – Historical suffix usage • “-ic” and “-ous” – Modern approach • English name of metal followed by Roman numeral indicating charge. Ionic Compound Formulas • Two Rules – Write symbol for positive ion first followed by the symbol for the negative ion – Assign subscripts to assure compound is electrically neutral using cross-over technique • Example: Calcium chloride. Covalent Compounds (AKA Molecules) • Held together by covalent bonds – Composed of two or more non-metals – Number of bonds determined by “valence” • Can be different elements or same elements – Carbon Tetrachloride (CCl4) ; Oxygen gas (O2) Covalent Compound Names Two rules • First element in formula named first with number indicated by Greek prefix • Stem name of second element next; Greek prefix for number; ending in “-ide” if only two elements are involved. Covalent Compound Formulas • Examples: carbon dioxide, carbon tetrachloride • Valence – Number of covalent bonds an atom can form – Hydrogen valence is 1 ; can only form single bonds – Oxygen is 2; single and double bonds – Nitrogen is 3; single, double and triple bonds – Carbon is 4 - single, double and triple bonds. Next: Chemical Reactions