You're right to think a solid bar of uranium would be incredibly dense! However, it's not the densest metal. Here's why:

* Density is mass divided by volume. While uranium has a high atomic weight, it's not the heaviest element.

* Osmium and Iridium are actually denser than uranium. They have smaller atomic radii and more tightly packed atoms, leading to a greater mass packed into a smaller volume.

Here's a quick comparison:

* Uranium: Density = 19.1 g/cm³

* Osmium: Density = 22.59 g/cm³

* Iridium: Density = 22.42 g/cm³

So, while uranium is indeed very dense, it's not the densest metal due to the slightly denser nature of osmium and iridium.