Copper is the most common mentioned metal that has the fcc structure. This element is one of the noble metals. It has been widely used for door knobs and other tools, and has been widely recognized. Yet, most noble metals (\(\ce{Cu}\), \(\ce{Ag}\), \(\ce{Au}\), \(\ce{Ni}\), \(\ce{Pd}\), \(\ce{Pt}\), \(\ce{Rh}\), and \(\ce{Ir}\)) have fcc type structures. Among the group 2 elements, only \(\ce{Ca}\) and \(\ce{Sr}\) have the fcc structure, whereas \(\ce{Be}\) and \(\ce{Mg}\) have hcp structures. So do \(\ce{Zn}\), \(\ce{Cd}\), \(\ce{Sc}\), \(\ce{Y}\), \(\ce{Lu}\), \(\ce{Ti}\), \(\ce{Zr}\), \(\ce{Hf}\), \(\ce{Tc}\), \(\ce{Re}\), \(\ce{Ru}\), \(\ce{Os}\) and most rare earth elements. These are mentioned to bring your attention to these two common types of structures, and you are encouraged to at least be able to give a few examples for each type. Amazingly, the hcp and fcc structure are very similar in many aspects, but nature knows best. The structures adopted by various metals occur by their design. When crystallization takes place, the atoms arrange themselves according to their structure types. Exercises 1 Copper has a specific gravity of 8.92; evaluate its atomic radius. The atomic radius of silver \(\ce{Ag}\) is listed as 145 pm. Evaluate its density.