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Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms

Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms. Objectives: Describe the trends in the periodic table Know how to draw Lewis Structures of atoms Understand and predict the formation of ionic bonds Understand and predict covalent bonds Describe electronegativity

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Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms

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  1. Chapter 11Chemical Bonds:The Formation of Compounds from Atoms Objectives: Describe the trends in the periodic table Know how to draw Lewis Structures of atoms Understand and predict the formation of ionic bonds Understand and predict covalent bonds Describe electronegativity Know how to draw complex lewis structures of compounds Understand the formation of compounds containing polyatomic ions Describe molecular shape, including the VSEPR model

  2. Periodic Trends in Atomic Properties • Periodic table designed to show trends • Use trends to predict properties and reactions between elements • Trends include: • Metals, nonmetals, metalloids • Atomic radius • Ionization energy • Electronegativity

  3. Metals, Nonmetals and Metalloids • Metals: • Left-hand side of table • Most elements are metals • Tend to

  4. Metals, Nonmetals and Metalloids • Nonmetals: • Right side of table • (Hydrogen displays nonmetallic properties under normal conditions but is UNIQUE element)

  5. Metals, Nonmetals and Metalloids • Metalloids • Found along border between metals and nonmetals • Metal + Nonmetal • Usually electrons are transferred

  6. Atomic Radius • Increases • Each step down = • More energy levels = • Decreases from • Electrons added to the same energy level • Increase in positive charge =

  7. Atomic Radius

  8. Ionization Energy • The energy required to • More energy required to remove 2nd, 3rd, 4th, 5th, etc. electron • Noble gas structure is stable so takes

  9. Ionization Energy • Ionization energy in Group A elements • Ionization energy • Metals – • Nonmetals –

  10. Ionization Energy

  11. Lewis Structures • Diagram that shows • American chemist Gilbert N. Lewis • Dots = • Paired dots = • Simple way of showing electrons • Most reactions involve only outermost electrons

  12. Lewis Structures • When drawing: • Use • Move in clockwise direction… • … • Examples: draw Lewis Structures of B, N, F, Ne

  13. The Ionic Bond • Ionic bond: • Transfer of electrons • Attraction between electrostatic charges is a strong force which holds atoms together

  14. The Ionic Bond • NOT A MOLECULE • Bond not just between (for example) one sodium and one chloride

  15. The Ionic Bond • Typically • Metals usually • Nonmetals usually

  16. Predicting Formulas of Ionic Compounds • In almost all stable chemical compounds of representative elements, each atom attains a noble gas electron configuration. This concept forms the basis for our understanding of chemical bonding.

  17. Predicting Formulas of Ionic Compounds • How many electrons must be gained or lost to achieve noble gas configuration? • Ba must • Forms the ion • S must • Forms the ion • So…

  18. Predicting Formulas of Ionic Compounds • Elements in a family usually form compounds with the same atomic ratios • Because they have the same number of valence electrons • Must gain or lose the same number of electrons • See table 11.4 pg 233

  19. Predicting Formulas of Ionic Compounds • The formula for sodium oxide is • Predict the formula for • Sodium sulfide

  20. Predicting Formulas of Ionic Compounds • Rubidium Oxide

  21. The Covalent Bond • A pair of electrons • Most common type of bond • Stronger • Electron orbital expands to include both nuclei • most often found between two nuclei • Negative charges allow positive nuclei to be drawn close to each other

  22. The Covalent Bond • Atoms may share more than one pair of electrons • Covalent bonding between identical atoms means • Covalent bonding between different atoms leads to

  23. Electronegativity • The attractive force that an atom of an element has for shared electrons • Atoms have different electronegativities

  24. Electronegativity • Electronegativity trends and periodic table • See table 11.5 page 237

  25. Electronegativity

  26. Electronegativity • Polarity is determined by difference in electronegativity • Nonpolar covalent • Polar covalent • Ionic compound

  27. Electronegativity • If the electronegativity difference is greater than 1.7-1.9 then the bond will be more ionic than covalent • Above 1.6 = ionic bond • Below 0.3 = nonpolar covalent • See Continuum on page 239

  28. Electronegativity • Polar bonds form between two atoms • Molecules can also be polar or nonpolar • Dipole • Polar • Nonpolar

  29. Lewis Structures of Compounds • Convenient way of showing ionic or covalent bonds • Usually the single atom in a formula is the central atom

  30. Lewis Structures of Compounds • Obtain the total number of valence electrons • Add the valance electrons of all atoms • Ionic – add one electron for each negative charge and subtract one electron for each positive charge

  31. Lewis Structures of Compounds • Write the skeletal arrangement of the atoms and connect with a single covalent bond • Subtract two electrons for each single bond • This gives you the net number of electrons available for completing the structure

  32. Lewis Structures of Compounds • Distribute pairs of electrons around each atom to give each atom a noble gas structure • If there are not enough electrons then try to form double and triple bonds

  33. Lewis Structures of Compounds • Write the Lewis Structure for methane CH4

  34. Complex Lewis Structures • Some molecules and polyatomic ions have strange behaviors… • No single Lewis structure is consistent • If multiple structures are possible the molecule shows

  35. Complex Lewis Structures • Carbonate ion, CO32- 2- 2- 2- Carbon only has 6 electrons – try double bonds – more than one location…..form resonant structures… O C O O O C O O O C O O

  36. Compounds ContainingPolyatomic Ions • Polyatomic ion: stable group of atoms that has a positive or negative charge • Behaves as a • Sodium carbonate (Na2CO3)

  37. Compounds ContainingPolyatomic Ions • Easier to dissociate ionic bond than break covalent bond • More in chapters 6 and 7

  38. Molecular Shape • Three-dimensional shape of molecule important • Helpful to know how to predict the geometric shape of molecules…

  39. The VSEPR Model • Valence Shell Electron Pair Repulsion Model • Make predictions about shape from Lewis structures

  40. The VSEPR Model • Linear Structure

  41. The VSEPR Model • Trigonal Planar

  42. The VSEPR Model • Tetrahedral structure • When drawing:

  43. The VSEPR Model • Pyramidal shape

  44. The VSEPR Model • Electron pairs determine shape BUT name for shape is determined by position of atoms

  45. The VSEPR Model • V-shaped or bent • But, moledule is “bent”

  46. The VSEPR Model • Predict the shape for CF4, NF3, and BeI2. • Draw the Lewis Structure • Count the electron pairs and determine the arrangement that will minimize repulsions • Determine the positions of the atoms and name the structure

  47. The VSEPR Model • CF4 • NF3

  48. The VSEPR Model • BeI2

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