TABLE 10.3 Van der Waals Constants for Gas Molecules Substance a (L²-atm/mol?) b (L/mol) Не 0.0341 0.02370 Ne 0.211 0.0171 Ar 1.34 0.0322 Kr 2.32 0.0398 Xe 4.19 0.0510 На 0.244 0.0266 N2 1.39 0.0391 O2 1.36 0.0318 F2 1.06 0.0290 Cl, 6.49 0.0562 Н-о 5.46 0.0305 NH3 4.17 0.0371 CH4 2.25 0.0428 CO2 3.59 0.0427 CCI4 20.4 0.1383 1A Н 2A 0.31 8A 7A 3A 4A БА 6A Be 0.96 He 0,28 Li 1.28 Ne 0,84 0.76 0.71 0.66 0.57 0,58 Increasing radius Mg 1.41 Na 1.66 Al Si P. Ar 1.21 1.11 1.07 |1.05 1.02 1.06 Kr a 60 1.53 1.39 1.391.32 |l.26 1.24 1.32 1.22 1.22 1.20 1.19 1,20 1.20 1.16 Cr Mn Fe Co Ni Cu Zn Ga Ca Sc Ti K 2.03 Ge As Se Br Sr Y. Zr Nb Mo Tc Ru Rh Pd Rb 1,95 190 1.75 1.64 1.54 147 1.46 1,42 1391451.44 1 42 139 1.39 1.38 1.39 1.40 Ag Cd In Sn Sb Te 2.20 Xe Radius (Å) Increasing radius Figure 7.7 Trends in bonding atomic radii for periods 1 through 5.
Ideal and Real Gases
Ideal gases obey conditions of the general gas laws under all states of pressure and temperature. Ideal gases are also named perfect gases. The attributes of ideal gases are as follows,
Gas Laws
Gas laws describe the ways in which volume, temperature, pressure, and other conditions correlate when matter is in a gaseous state. The very first observations about the physical properties of gases was made by Robert Boyle in 1662. Later discoveries were made by Charles, Gay-Lussac, Avogadro, and others. Eventually, these observations were combined to produce the ideal gas law.
Gaseous State
It is well known that matter exists in different forms in our surroundings. There are five known states of matter, such as solids, gases, liquids, plasma and Bose-Einstein condensate. The last two are known newly in the recent days. Thus, the detailed forms of matter studied are solids, gases and liquids. The best example of a substance that is present in different states is water. It is solid ice, gaseous vapor or steam and liquid water depending on the temperature and pressure conditions. This is due to the difference in the intermolecular forces and distances. The occurrence of three different phases is due to the difference in the two major forces, the force which tends to tightly hold molecules i.e., forces of attraction and the disruptive forces obtained from the thermal energy of molecules.
Table 10.3 shows that the van der Waals b parameter has
units of L/mol. This implies that we can calculate the size of
atoms or molecules from b. Using the value of b for Xe, calculate
the radius of a Xe atom and compare it to the value
found in Figure 7.7, that is, 1.40 Å. Recall that the volume of
a sphere is (4/3)πr3
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