Question

1. Determine whether each statement below is True (T) or False (F). a. ____ If A,B and C are elements whose electronegativities satisfy xA > xB > xC, then then (ΔAC)1/2 = (ΔAB)1/2 + (ΔBC)1/2 if the Pauling electronegativity scale is valid. b. ____ There is no interelectronic repulsion in the H2+ molecule. c. ____ The wave function N(1sA + 1sB) is the exact electronic wave function for the ground electronic state of H2+. d. ____ The plane perpendicular to the molecular axis at the midpoint between the nuclei in H2+ is a node for the first excited state. e. ____ The molecular electron probability density is experimentally observable. f. ____ The molecular wave function is experimentally observable. g. ____ The bonding MOs of BeH2 extend over all three atoms and the hybridization of AOs are approximately sp2. h. ____ A SCF wave function is one in which each electron is assigned to a single spin-orbital, the spatial part of each spin-orbital is expressed as a non- linear combination of basis functions, and the coefficients in these combinations are found by solving the Hartree-Fock equations. i. ____The molecular-mechanics method is an empirical quantum mechanical method that treats the molecule as atoms held together by bonds and writes the molecular steric energy as the sum of contributions from bond bending and stretching, bond torsion and van der Waals and electrostatic interactions of non-bonded atoms. j. ____ The molecular-mechanics method can be applied to very large molecules and yields good results when applied to molecules similar to those for which the force field was parametrized. k. ____ The maximum electron probability density in the ground electronic state of H2+ occurs at each nucleus. l. ____ If sufficient basis functions are used, the Hartree-Fock wave function of a many-electron molecule will reach the true wave function. m. ____ In a homonuclear diatomic molecule, combining two 2p AOs always yields a π MO. n. ____ In homonuclear diatomic molecules, all u MOs are antibonding. o. ____ A decrease in viscosity with increasing rate of flow of a solution indicates the presence of long rod-like molecules that are orientated by the flow.

Answer 1

a. True (because the pauling electronegativity scale is linear)

Consider; xA=3 > xB=2 > xC=1

Now (ΔAC)1/2 = (ΔAB)1/2 + (ΔBC)1/2 is valid as (3-1)/2 = (3-2)/2 + (2-1)/2

b. True (beacuse H₂⁺ molecule contains only one electron)

c. False (having two bonding orbitals and a single electron there should be a spin exchange term in the wave function, which is not present in the given additive expression N(1sA + 1sB))

d. True ( the nodal plane of the first excited state of H₂⁺ molecule lies perpendicular to the molecular axis at the midpoint between the nuclei)

e. True (it is ² observable in STM experiments)

f. False (it is , a mathematical entity)

g. False (BeH₂ is linear and sp hybridized)

h. True (all statements are correct)

i. True (it considers all the given forces, bending and stretching and bond torsion are the covalent forces while van der Waals and electrostatic interactions are the non-covalent forces)

j. True (a well parameterized force field benchmarked with ab-initio calculations represents the quantum mechanical potential field for the molecule)

k. True (that is why it does not exist hence collapses)

l. True (the sufficiency of the basis sets is abnormally high)

m. True (there will always be two p-orbitals with the same angular/azimuthal quantum number)

n. False (The ungerade orbitals can be non-bonding as well)

o. True (the increasing flow will increase the velocity of the medium around the edges of the rod-like molecule and hence the viscosity will decrease)