The number of moles corresponding to V m is
3:3 Â 10
−8 m
3
2:24 Â 10
−2 m 3 mol−1
= 1:47 Â 10
−6 mol
The number of molecules is simply N A times the number of moles.
6:022 Â 10
23 mol
– 1
1:47 Â 10
– 6 mol
= 8:85 Â 10
17 molecules
Now each N 2 molecule occupies a single site on the mica surface.
Thus, there must be 8.85 × 10
17 sites on the surface.
For a square of length 2 cm, the concentration of surface sites is
simply the ratio of the total number of sites to the total surface
area of the square.
8:85 Â 10
17 molecules
0:02m
ð
Þ
2
= 2:21 Â 10
21 m
−2
9 × 10 7
6 × 10 7
7 × 10 7
8 × 10 7
5 × 10 7
4 × 10 7
3 × 10 7
2 × 10 7
1 × 10 7
1 × 10 12 2 × 10 12 3 × 10 12 4 × 10 12 5 × 10 12 6 × 10 12
0
0
1/[V(m 3
)]
1/[P(torr)]
Figure 7.11 A plot of 1/V
versus 1/P for the adsorption
of N 2 on mica at 273.15 K.
ADSORPTION PHENOMENA: SELF-ASSEMBLED MONOLAYERS 239