Chapter 6.2<br />Covalent bonding and molecular compounds<br />
Objectives:<br />Define molecule and molecular formula.<br />Explain the relationships between potential energy, distance ...
Molecular compounds<br />Molecule – <br />Neutral group of atoms that are held together by covalent bonds<br />Compose mos...
Chemical compound whose simplest units are molecules</li></li></ul><li>Molecular compounds<br />Chemical formula – <br />I...
Shows the types and numbers of atoms combined in a single molecule of a molecular compound
H2O  			CO2   		C12H22O11
Diatomic molecule –
Molecule containing only two atoms
H2		O2		N2</li></li></ul><li>Formation of a Covalent Bond<br />Nature favors bonding because<br />Puts atoms at lower pote...
Attractedto each
Decrease in potential energy
At the same time, both nuclei and two electrons
repel each other
Increase in potential energy</li></ul>Electron Negative<br />Positive Nucleus<br /><ul><li>Potential energy is minimized w...
The energy required to break a chemical bond and form neutral isolated atoms
As the bond energy increases-
The bond length decreases</li></li></ul><li>Bond length<br />
Octet Rule<br />Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet ...
The eight electrons come from the main-group energy levels being filled.
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Chapter 6.2 : Covalent Bonding and Molecular Compounds

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Chapter 6.2 : Covalent Bonding and Molecular Compounds

  1. 1. Chapter 6.2<br />Covalent bonding and molecular compounds<br />
  2. 2. Objectives:<br />Define molecule and molecular formula.<br />Explain the relationships between potential energy, distance between approaching atoms, bond length, and bond energy.<br />State the octet rule<br />List the six basic steps used in writing Lewis structures.<br />Explain how to determine Lewis structures for molecules containing single bonds, multiple bonds, or both.<br />Explain why scientists use resonance structures to represent some molecules<br />
  3. 3. Molecular compounds<br />Molecule – <br />Neutral group of atoms that are held together by covalent bonds<br />Compose most living things<br /><ul><li>Molecular compound–
  4. 4. Chemical compound whose simplest units are molecules</li></li></ul><li>Molecular compounds<br />Chemical formula – <br />Indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts<br />H2O CO2 C12H22O11<br /><ul><li>Molecular formula –
  5. 5. Shows the types and numbers of atoms combined in a single molecule of a molecular compound
  6. 6. H2O CO2 C12H22O11
  7. 7. Diatomic molecule –
  8. 8. Molecule containing only two atoms
  9. 9. H2 O2 N2</li></li></ul><li>Formation of a Covalent Bond<br />Nature favors bonding because<br />Puts atoms at lower potential energy<br /><ul><li>Approaching nuclei and electrons
  10. 10. Attractedto each
  11. 11. Decrease in potential energy
  12. 12. At the same time, both nuclei and two electrons
  13. 13. repel each other
  14. 14. Increase in potential energy</li></ul>Electron Negative<br />Positive Nucleus<br /><ul><li>Potential energy is minimized when attractive forces are equal to the repulsive forces</li></li></ul><li>Characteristics of Covalent Bond<br />Bond length – <br />The distance between two bonded atoms at their minimum potential energy, that is, the average distance between two bonded atoms<br /><ul><li>Bond Energy –
  15. 15. The energy required to break a chemical bond and form neutral isolated atoms
  16. 16. As the bond energy increases-
  17. 17. The bond length decreases</li></li></ul><li>Bond length<br />
  18. 18. Octet Rule<br />Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level.<br /><ul><li>Hydrogen is an exception because it is stable with 2 electron in outer shell.
  19. 19. The eight electrons come from the main-group energy levels being filled.
  20. 20. s2p6 totals 8 electrons</li></li></ul><li>Bonding and octet rule<br />F __ __ __ __ __<br /> 1s 2s 2p<br />F __ __ __ __ __<br /> 1s 2s 2p<br />Bonding electron pair in overlapping orbitals<br />Li __ __<br /> 1s 2s<br /> F __ __ __ __ __<br /> 1s 2s 2p<br />
  21. 21. Exceptions to the Octet Rule<br />Most main-group elements<br />Tend to form covalent bonds according to octet rule<br /><ul><li>Exceptions
  22. 22. Hydrogen – forms bonds where it is surrounded by only two electrons
  23. 23. Boron - has just 3 valence electrons, so it tends to form bonds in which it is surrounded by six electrons
  24. 24. BH3</li></ul> H<br /> B<br /> H H<br />
  25. 25. Electron-Dot Notation<br />Electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the elements symbol<br />Dots – valence electrons<br />Symbol – nucleus and inner-shell electrons<br /> I<br />7 Valence electrons<br />53 protons<br />73 neutrons<br />36 inner shell electrons<br />
  26. 26. Electron-Dot Notation<br />First three rows of periodic table<br />Group<br /> 1 2 13 14 15 16 17 18<br />
  27. 27. Lewis Structures<br />Formulas in which atomic symbols represent nuclei and inner-shell electrons, dot-pair or dashes and dots between two atomic symbols represent electron pairs in covalent bonds, and dots adjacent to only one atomic symbol represent unshared electrons.<br /><ul><li>Unshared pair ( lone pair ) –
  28. 28. Pair of electrons that is not involved in bonding and that belongs exclusively to one atom
  29. 29. Structural formula –
  30. 30. Indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule
  31. 31. Single Bond –
  32. 32. Covalent bond produced by the sharing of one pair of electrons between two atoms.</li></ul>B F <br />B – F <br />
  33. 33. Draw the Lewis Structure of iodomethane, CH3I<br />1. Determine the type and number of atoms in the molecule<br />1 C 3 H 1 I<br />2. Write the electron-dot notation for each type of atom in the molecule<br /> C H I<br />3. Determine the total number of valence electrons in the atoms to be combined<br />C 1 x 4e-= 4e-<br />H 3 x 1e- = 3e-<br />I 1 x 7e- = 7e-<br /> 14e-<br />Total valence electrons<br />
  34. 34. 4. Arrange the atoms to form a skeleton structure for the molecule. IfCarbonis present, it is the central atom. Otherwise, the least-electronegative atom is central (except for hydrogen, which is never central). Then connect the atoms by electron-pair bonds.<br /> H<br />H C I<br /> H<br />5. Addunshared pairs of electrons so that each hydrogen atom shares a pair of electrons and each other nonmetal is surrounded by eight electrons<br /> H<br />H C I<br /> H<br />6. Count the electrons in the structure to be sure that the number of valence electrons used equals the number available. Be sure the central atom and other atoms besides hydrogen have an octet.<br />14 e- so this is correct!!!<br />
  35. 35. Multiple Covalent Bonds<br />Double bond –<br />Covalent bond produced by the sharing of two pairs of electrons between two atoms<br />H H<br /> C C<br />H H<br />H H<br /> C C<br />H H<br />OR<br /><ul><li>Triple bond –
  36. 36. Covalent bond produced by the sharing of three pairs of electrons between two atoms</li></ul> N N<br /> N N<br />OR<br />
  37. 37. Draw the Lewis Structure for methanal, CH2O, which is also known as formaldehyde.<br />1. Determine the type and number of atoms in the molecule<br />1 C 2 H 1 O<br />2. Write the electron-dot notation for each type of atom in the molecule<br /> C H O<br />3. Determine the total number of valence electrons in the atoms to be combined<br />C 1 x 4e-= 4e-<br />H 2 x 1e- = 2e-<br />O 1 x 6e- = 6e-<br /> 12e-<br />
  38. 38. 4. Arrange the atoms to form a skeleton structure for the molecule. IfCarbonis present, it is the central atom. Otherwise, the least-electronegative atom is central (except for hydrogen, which is never central). Then connect the atoms by electron-pair bonds.<br /> H<br />H C O<br />5. Addunshared pairs of electrons so that each hydrogen atom shares a pair of electrons and each other nonmetal is surrounded by eight electrons<br /> H<br />H C O<br />6. Count the electrons in the structure to be sure that the number of valence electrons used equals the number available. Be sure the central atom and other atoms besides hydrogen have an octet.<br /> H<br />H C O<br /> H<br />H C O<br />OR<br />14 e- = 12 e-<br />SO<br />
  39. 39. Resonance Structures<br />Bonding in molecules or ion that cannot be correctly represented by a single Lewis structure.<br />O O O<br />O O O<br />Or<br />
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