B 6 points consider the alkali halide system kcl with

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Chemistry & Chemical Reactivity
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Chapter 7 / Exercise 24
Chemistry & Chemical Reactivity
Kotz/Treichel
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(b) (6 points) Consider the alkali halide system KCl with an unknown lattice energy X . Which of the ionic substances described above would you expect to have a lattice energy most similar to that of X ? Would X be larger or smaller than your choice? Explain your answer; most of the credit will be assigned for a correct explanation, and not just a correct guess. 9
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Chemistry & Chemical Reactivity
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Chapter 7 / Exercise 24
Chemistry & Chemical Reactivity
Kotz/Treichel
Expert Verified
7. (a) (24 points) Below is shown a model MO diagram describing a generic heteronuclear diatomic molecule AB where the “heavy-atom” orbital energies are assumed, as shown. For the transient diatomic NF fill in the MO diagram; make sure that you identify which atom (N or F) corresponds to the A or B species in the diagram, and that you place the valence electrons both into AO’s and MO’s as appropriate. Based on your MO diagram, also answer the questions below. i. Identify the bond order in the NF molecule. ii. The bond length in NF is measured to be 135 pm; in the ion NF + , it is found to be 124 pm. Does your MO diagram provide an explanation for the shortening of the NF bond when an electron is lost? Explain. 10
iii. In creating the ion, an electron is removed from the highest occupied MO (the HOMO). Based on your diagram, does the HOMO correspond to greater electron density on the N or on the F atom? iv. List any species (NF or NF + ) which is paramagnetic. (b) (8 points) The OH radical has been observed in interstellar space. Sketch and label an MO diagram indicating which of the valence orbitals only on the two atoms are involved in bonding; on your MO diagram you should indicate which orbitals are occupied both in the separated atoms and in the diatomic molecule. 11
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Some possibly useful facts: For the one-electron atom, the ionization energy of the n th Bohr state for nuclear charge Z is IE n = 2 . 18 aJ Z 2 n 2 If one knows the ionization energy IE n,‘ of a specific electron with known values of { n, ‘ } then IE n,‘ = 2 . 18 aJ Z 2 eff n 2 can be taken as a definition of Z eff . Coulomb’s law states that for two ions of charge Q 1 and Q 2 separated by a center-to-center distance r 12 the electrostatic energy of interaction is E = 231 (aJ - pm) Q 1 Q 2 r 12 Negative values of E correspond to an attractive interaction. p )(Δ x ) h 4 π λ = h mv The mass of the neutron is m n = 1 . 675 × 10 - 27 kg The mass of the proton is m p = 1 . 673 × 10 - 27 kg The mass of the electron is m e = 9 . 109 × 10 - 31 kg 6 . 022 × 10 23 amu = 1 gram (exactly) E photon = = hc λ h = 6 . 626 × 10 - 34 Joule - sec c = 2 . 998 × 10 8 meter / sec 1 watt = 1 Joule/sec 13
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