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Chapter 9: Models of Chemical Bonding

Chapter 9: Models of Chemical Bonding. Lewis Dot Symbols Ionic Bonding Metallic Bonding Covalent Bonding Polar Bonds Electronegativity. Lewis symbols. Practice. Give Lewis dot symbols for:. Oxide ion. magnesium. Sodium ion. nitrogen. fluorine. argon. boron.

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Chapter 9: Models of Chemical Bonding

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  1. Chapter 9: Models of Chemical Bonding • Lewis Dot Symbols • Ionic Bonding • Metallic Bonding • Covalent Bonding • Polar Bonds • Electronegativity

  2. Lewis symbols

  3. Practice • Give Lewis dot symbols for: Oxide ion magnesium Sodium ion nitrogen fluorine argon boron

  4. Types of Bonding and Properties Ionic Metallic Covalent

  5. Ionic Bonding • Ionic compounds form • The attraction • Forming ions takes energy

  6. Metallic Bonding • Outer electrons • Large numbers of metal atoms • The electrons are ‘delocalized’

  7. Covalent Bonds

  8. Network Covalent Solids http://www.hull.ac.uk/chemistry/intro_inorganic/images/diamond.jpg

  9. Polar Covalent Bonds • When two identical atoms form a covalent bond • When different kinds of atoms combine,

  10. (a) • (b)

  11. Electronegativity • In general, electronegativity increases

  12. http://www.chem.ufl.edu/~itl/2045/change/C9F16.GIF

  13. The difference in electronegativity • There is no sharp dividing line between ionic and covalent bonding: • A bond is mostly ionic when

  14. The degree of polarity, or ionic character, varies continuously with the electronegativity difference Each atom in a bond has a partial charge of about +0.5 or –0.5 units when the electronegativity difference is 1.7.

  15. Practice Questions • Identify the following bonds as • Mostly ionic • Polar Covalent • Mostly Covalent • Nonpolar Covalent C-Cl Re-H Li-Cl P-H Sn-Br Sr-O

  16. Lewis symbols can be used to represent the covalent or electron pair bond • Formulas drawn with Lewis symbols are called Lewis formulas or Lewis structures

  17. The term structural formula • Many molecules obey the octet rule: • The number of bonds an atom (second-row) forms is determined by:

  18. C Has 4 e- Needs 4 e- Forms 4 bonds N O F B Number of Bonds

  19. single bond • Double and triple bonds • The bond order • A single bond has bond order of • a double bond a bond order of • a triple bond a bond order of • Bond length depends on bond order:

  20. Drawing Lewis Structures • The least electronegative atom is usually in the middle. (Or the atom which can form the most bonds.) • Count total number of valence electrons in molecule/ion. • Place them around the atoms to satisfy the octet rule:

  21. Phosphorus Trichloride Carbon Dioxide

  22. Not all structures obey the octet rule

  23. Sulfur tetrafluoride Bromine pentafluoride

  24. The preferred Lewis structure is the one that best fits the experimental data The structure of sulfuric acid in the vapor state. There are two different sulfur-oxygen bond lengths. The preferred Lewis structure needs different bond orders for these atoms.

  25. Structure I • Structure II

  26. formal charge • The formal charge on an atom is calculated

  27. Consider the sulfur atoms in the two structures for sulfuric acid: Structure I: formal charge on S = Structure II: formal charge on S = • When several Lewis structures are possible,

  28. Nitrate ion Iodate ion Formal charge on O = Formal charge on I = Formal charge on O = Formal charge on I =

  29. Some molecules and ions are not well represented by a single Lewis structure • Consider the case of the formate ion, HCO2- • Experiment gives • These are called resonance structures

  30. Draw the resonance forms for nitrate. Draw resonance forms for thiosulfate. Draw the resonance forms for dinitrogen monoxide.

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