Chapter Seven Text

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  1. When two hydrogen atoms come close together, __ begin to develop between them. What happens with the nuclei and electrons?
    • electrostatic interactions
    • the two positively charged nuclei repel each other, and the two negatively charged electrons repel each other, but each nucleus attracts both electrons
  2. If the attractive forces are __ than the __ forces, a covalent bond is formed, with the two atoms __ and the two shared eletrons __.
    • stronger
    • repulsive
    • held together
    • occupying the region between the nuclei
  3. The __ of hte various attractive and repulsive forces between __ and __ in a __ depend on how close the atoms are. 
    • magnitudes
    • nuclei
    • electrons
    • covalent bond
  4. If the atoms are too far apart, what happens? too close?

    Thus, there is an optimum distance between nuclei called the __ where net attractive forces are maximized and the H-H molecule  is most stable.
    • far: attractive forces small and no bond exists
    • repulsive interaction between nuclei becomes so strong it pushes atoms apart
    • bond length
  5. Every __ has its own characteristic length that leads to __ and that is roughly predictable from a knowledge of __.
    • covalent bond
    • maximum stability
    • atomic radii
  6.  Bond dissociation energies are always ___. Why?
    • positive
    • energy must be supplied to break a bond
  7. The amount of energy released on forming a bond always has a __ value.
  8. Why are ionic compounds high-melting solids?

    Fpr sodium chloride to melt or boil so that the ions break free of one another, every ionic attraction int the entire crystal--the __-- must be overcome, a process that requires a large amount of energy.
    • ionic bonds
    • lattice energy
  9. What symbol represents the resultant partial charges on the atoms?
    lowercase Greek letter delta
  10. maps that use olor to portray the calculated electron distribution in an isolated, gas-phase molecule.
    electrostatic portential maps
  11. Where are the least EN items found? highest?
    • lowest from top to bottom
    • highest from left to right
  12. The pairs of electrons that are nonbonding
    lone pairs
  13. shared electrons 
    bonding pair
  14. In speaking of moolecules with multiple bonds, we often use the term __ to refer to the number of electron pairs shared between atoms.
    bond order
  15. bonds that form when one atom donates a lone pair to another atom that has a vacant valence orbital
    coordinate covalent bonds
  16. When the octet rule fails, it often does so for elements toward the __ of the periodic table that are in the __ row and lower.
    • right side
    • third
    • They are larger, can accomodate more than four atoms close around them, and therefore form more than four bonds
  17. Resonance hybrid
    the actual electronic structure is an average of the different possibilities
  18. How to calculate formal charge?
    number of valence in free atom- (1/2) Number of bonding electrons- number of nonbonding electrons
  19. The number of charge clouds is the __.
    total bumber of bonds and lone pairs
  20. Both the electron dot model and VSEPR model do not say what?
    say anything about the electronic nature of covalent bonds
  21. To describe bonding, a quantum mechanical model called __ has been developed. It provides an easily visualized orbital picture of how electron pairs are shared in a covalent bod. 
    valence bond theory
  22. In the valence bond model, the two overlapping lobes must be of the __, and teh strength of the covalent bond that forms depends on the amount of __ overlap: the __ the overlap, the __ the bond.
    This, in turn, means that bonds formed by overlap of other than s orbitals have a __ to them.
    • phase
    • orbital overlap
    • greater
    • stronger
    • directionality
  23. Such bonds that result from head-on orbital overlap are called __.
    sigma bonds
  24. What are the principles of valence bond theory?
    • covalent bonds are formed by overlap of atomic orbitals, each of which contains one elctron of opposite spin. The two overlapping lones must be of the same phase. 
    • Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms. 
    • The greater the amount of orbital overlap, the stronger hte bond. This leads to a directional character for the bond when other than s orbitals are involved.
  25. How can carbon form four bonds if two of its valence electrons are already paired and only two unpaired electrons remain for sharing?
    • electron must be promoted from the lower energy 2s orbital to the vacant, higher-energy 2pz orbital, giving an excited state configuration [He] 2s2px1 2py1 2pz1 that has foour unpaired electrons and can thus form four bonds
  26. Linus Pauling introduced the idea of __. Pauling showed how the __ for s and p atomic orbitals derived from the __ can be mathematically combiined to form a new set of equivalent wave unctions called __.
    Ex: When one s orbital combines with three p orbitals, as occurs in an __, four equivalent hybrid orbitals, called __, result. 
    • hybrid orbitas
    • quantum mechanical wave functions
    • Schrodinger wave equation
    • hybrid atomic orbitals
    • excited-state carbon atom
    • sp3 orbitals 
  27. Each sp3 hybrid ornital has two lobes, of __,one of which is larger than the other.
    different phase
  28. The shared electrons in a covalent bond made with a spatially directed hybrid orbital spend most of hteir time in the region between the __.
    two bonded nuclei
  29. Atoms with three charge clouds undergo hybridization by combination of one atomic s orbital with two p ornitals, resulting in three __.
    sp2 hybrid orbitals
  30. What happens to the unhybridized p orbitals on the carbons as the two sp2 hybridized carbon atoms approach each other with sp2 orbitals aligned head-on for sigma bonding?
    the unbybridized p orbitals on the carbons approach oeach other in a parallel, sideways manner rather than head on, occupying regions above and below a line connecting hte nuclei rather than directly, called a pi bond
  31. The __ bond has __ regions of orbital overlap, one above and one below a line drawn between the nuclei, the __. Both regiosn are part of the same bond, and the two shared electrons are spread over both regions. As always, the p lobes must be of the same __ for overlap, leading to __. The net reaction of both sigma and pi bonds is __.
    • pi
    • two
    • internuclear axis
    • phase
    • the sharing of four electrons and the formation of a carbon-carbon double bond
  32. A given shell has a total onf only __ s and p orbitals.
  33. 2 charge clouds
    Arrangement and hybridization?
    • linear
    • sp
  34. 3 charge clouds
    Arrangement and hybridization?
    trigonal planar sp2
  35. 4 charge clouds 
    Arrangement and hybridization?
    • tetrahedral
    • sp3
  36. Atomic orbitals on the same atom can do what?
    combine to form hybrids
  37. Atomic orbitals on different atoms can overlap to do what?
    form covalent bonds, but the orbitals and electrons in htem remain localized on specific atoms
  38. atomic orbital
    a wave function whose square gives hte probability of finding an electron within a given region of space in an aotom
  39. Molecular orbital theory considers what?
    the molecule as a whole rather than the individual atoms
  40. molecular orbital
    a wave function whose square gives the probability of finding an electron within a given region of space in a molecule
  41. Molecular orbital theory has two ways for interaction...__ and __
    additive nad subtractive way
  42. The additive combo, denoted sigma, is __ in energy than the two isolated 1s orbitals and is called a __ because any electrons it contains spends most of their tiime in the region between the two nuclei, bonding the atoms together.
    • lower
    • bonding molecular orbital
  43. In the molecular orbitals, a net gain results in __, while a neutral (no net bondign energy) results in __.
    • stability
    • instability
  44. bond orders
    the number of electron pairs shared between atoms
  45. how to determine bond order?
    (# of bonding electrons- # of antibonding electrons)/2 
  46. A molecular orbital describes what?
    a region of space in a molecule where electrons are most likely to be found, and it has a specific size, shape, and energy level
  47. Molecular orbitals are formed how?
    by combining atomic orbitals on different atoms
  48. Molecular orbitals are __ in energy than the starting atomic orbitals are __, and MOs that are __ in energy than the starting atomic orbitals are __.
    • lower
    • bonding
    • higher
    • antibonding
  49. Electrons occupy molecular orbitals beginning with the __. A maximum of __ electrons can occupy each orbital, and their spins are paired.
    • MO of lowest energy
    • two
  50. Substances with unpaired electrons are attracted by magnetic fields and are thus said to be __.
  51. The more unpaired electrons a substance has, the stronger the __ attraction.
  52. Substances whose electrosn are all spin-paired, by contrast, are weakly repelled by magnetic fields and are said to be __.
  53. __ is better because of its simplicity and ease of visualization, but __ is better because of its accuracy.
    • valence bond theory
    • MO theory
  54. What are the two problems with valence bond theory?
    • for olecules like O2, it makes an incorrect prediction about electronic structure
    • for molecules like O3, no single structure is adequate and resonance must occur
  55. spread out
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Chapter Seven Text
2012-11-28 01:58:43

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