26)Which of the following molecules are polar? I SO3 Il. NCI3 III. PCIs a. Ionly

Question

26)Which of the following molecules are polar? I SO3 Il. NCI3 III. PCIs a. Ionly b. Il only c. land II only d. I and IIl only e. Il and IlI only 27)Which of the following statements is true a. The de Broglie wavelength of a flying bullet is longer than that of a red b. A 2p orbital has 2 radial nodes. c. If a molecule has a plane of symmetry it cannot be polar. d. A hydrogen atom has 2s orbitals e. Electrons are shared equally in the H-F covalent bond. 28)The ionization en ergy for the He+ ion (n=1 to n=oo) is th because the eff charge of the H atom. a. higher bigger thar b. higher smaller than igher d. lower e. lower equal to bigger than smaller than GenChem I all 2017 Exam 2B

Explanation / Answer

26. OPTION B. Polarity of a molecule is a measure of its resultant dipole moment arising from the sum of all individual dipole vectors. If the net dipole moment is zero, the molecule is non-polar and if its not zero, it is polar. In case of sulfur trioxide, the trigonal planar molecular geometry with the dipole vectors arising from the sulfur to oxygens gives equal dipoles on all directions, cancelling them out overall. This makes sulfur trioxide non-polar. For nitrogen trichloride N is less electronegative than Cl. Moreover, the molecule has all 3 Cl atoms pointing downward in the trigonal pyramidal geometry resulting in a net dipole vector pointing downward perpendicular to the principal C3 axis of the molecule. Thus, the molecule is polar. PCl5 is non-polar as the three equitorial Cl atoms cancel the dipole moment perpendicular to the principle axis of the molecule similar to sulfur trioxide and the two equivalent axial Cl pull equally above and below cancelling out dipole moment along the axis too.

27. OPTION D. de Broglie wavelength is inversely propotional to the mass and velocity of the object (object's momentum). Hence, if the flying bullet is lighter than the red object (Exact object is not visible in question) and faster than the latter, this statement is true. If however the red object is propotionally faster than the bullet such that both their momentums are equal, then the statement is false. The no.of radial nodes of a np orbital is related to its principal quantum number as (n-2) radial nodes for a np orbital. So for 2p orbital, we get (2-2) = 0 radial nodes. Even if a molecule has a plane of symmetry, it can have a net dipole moment depending upon the molecular geometry, it can have a dipole moment. Since a hydrogen has only 1 atom, in its ground state, it does not have a 2s orbital. However, since the state of the atom is not mentioned, theoretically, electron excitation results in electron going to 2s orbital so we can say H atom has 2s orbital. HF molecule is very polar due to the large electronegativity difference between H and F atoms. This reuslts in the electron cloud of the molecule to be distorted by the F atom due to its pull of electrons toward itself. So only the fourth statement is true.

28.OPTION A. He has more nucleons than H resulting in a higher effective nuclear charge for He cation. Hence, the electron remaining will be pulled more towards the nucleus of He cation that the electron in an H atom. So the ionization energy of He cation is higher than that of H atom and its effective nuclear charge is bigger than that of H atom.

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