1 (176)

Prévia do material em texto

7 Periodic Properties of the Elements Solutions to Exercises interpenetrate, bringing the two nuclei closer together and resulting in a smaller bonding atomic radius (Figure 7.5). (d) If a free atom reacts to become part of a covalent molecule, the atom gets smaller; its radius changes from nonbonding to bonding. 7.18 (a) Since the quantum mechanical description of the atom does not specify the exact location of electrons, there is no specific distance from the nucleus where the last electron can be found. Rather, the electron density decreases gradually as the distance from the nucleus increases. There is no quantum mechanical "edge" of an atom. (b) When nonbonded atoms touch, it is their electron clouds that interact. These interactions are primarily repulsive because of the negative charges of electrons. Thus, the size of the electron clouds determines the nuclear approach distance of nonbonded atoms. 7.19 (a) The atomic (metallic) radius of W is the interatomic W-W distance divided by 2, 2.74 Å/2= 1.37 Å. (b) Under high pressure, we expect atoms in a pure substance to move closer together. That is, the distance between W atoms will decrease. 7.20 The distance between Si atoms in solid silicon is two times the bonding atomic radius from Figure 7.6. The Si-Si distance is 2 1.11 Å = 2.22 Å. The C-C distance in diamond is 1.54 Å (from Section 7.3; from Figure 7.6, 2 X 0.77 Å = 1.54 Å). We expect the Si-Si distance to be greater, because the bonding (valence) electrons in Si are in the n=3 shell, while those in C are in the n=2 shell. 7.21 From bonding atomic radii in Figure 7.6, As-I = 1.19 Å + 1.33 Å = 2.52 Å. This is very close to the experimental value of 2.55 Å in AsI₃. 7.22 Bi-I = 2.81 Å = + r₁. From Figure 7.6, = 1.33 Å. = - r₁ = 2.81 Å - 1.33 Å = 1.48 Å. 7.23 (a) Atomic radii decrease moving from left to right across a row and (b) increase from top to bottom within a group. (c)