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QUESTION

At 20°C, the density of copper is 8.9 g/cm^3. The density of platinum is 21.4 g/cm^3. What does this tell you about how the atoms are "packed" in each material?

Good question. Remember, that we compare a 3rd row transition metal (Pt), to a 1st row transition metal (Cu).

"Molar mass (Cu)" = 63.55 g*mol^-1.

"Molar mass (Pt)" = 195.08 g*mol^-1.

This threefold difference in molar mass, of course translates to . Given that the difference in densities is (very approx.) threefold as well, we would predict that the atomic packing in both metals is similar in terms of , "mass per unit volume". Does this make sense?