Impurities in Solids 6.9 Atomic radius, crystal structure, electronegativ- ity, and the most common valence are tabulated in the following table for several elements, for those that are nonmetals, only atomic radii are indicated. Atomic Radius (nm) Crystal Structure Electro- negativity Valence Element Cu 0.1278 FCC 1.9 +2 C 0.071 H 0.046 O 0.060 0.1445 FCC 1.9 +1 Ag Al 0.1431 FCC 1.5 +3 Co 0.1253 HCP 1.8 +2 Cr 0.1249 BCC 1.6 +3 Fe 0.1241 BCC 1.8 +2 Ni 0.1246 FCC 1.8 +2 Pd 0.1376 FCC 2.2 +2 Pt 0.1387 FCC 2.2 +2. Zn 0.1332 HCP 1.6 +2 Which of these elements would you expect to form the following with copper: (a) A substitutional solid solution having com- plete solubility (b) A substitutional solid solution of incomplete solubility (c) An interstitial solid solution