19. Answer the following:
(a) Sketch the sigma (?) bond that is created by the overlap of two p orbitals.
(b) Sketch the pi (?) bond that is created by the from the overlap of two p orbitals
(c) Which is generally the stronger, a sigma (?) bond or a pi (?) bond? Explain.
20. For each of the following molecules or ions of sulfur and oxygen, write a single Lewis structure that
obeys the octet rule, and calculate the oxidation numbers and formal charges on all the atoms:
(a) SO$_2$, (b) SO$_3$, (c) SO$_3$$^{2-}$ (d) Arrange these molecules/ions in order of increasing bond length
and increasing bond strength. (Hint: Think about resonance structures.)
21. Do the following:
(a) Sketch the molecular orbitals of the H$_2$$^-$ ion and draw its energy level diagram.
(b) Write the electron configuration of the ion in terms of its MOs.
(c) Calculate the bond order in H$_2$$^-$.
(d) Suppose that the ion is excited by light, so that an electron moves from a lower energy to a
higher energy molecular orbital. Would you expect the excited state H$_2$$^-$ to be stable? Explain.
