As we have seen (Fig. 8.11), the bonds between atoms can be represented by vectors. The atoms in a water molecule (H2O, with atoms O, H1 and H2

) are positioned at the coordinates (in units of Å)

O = (0, 0, 0), H 1 = (0.950, 0, 0), H 2 = (−0.238, 0.920, 0).

a. Use these coordinates to construct the vectors

−−−→

OH1 and

−−−→

OH2

, and thus construct a diagram of an H2O molecule.

b. What is the bond angle?

c. What are the bond lengths?

d. What is the distance between the two H atoms?

e. When the atoms vibrate, they absorb light with an electromagnetic oscillation in the corresponding net direction of that vibration. One of the vibrational modes of water involves the symmetrical stretching of the OH1 and OH2 bonds. If each bond is lengthened by 2% what is the percentage change in the distance between H1 and H2 ?