Atomic/molecular level definition/description of density.

[TFGordon]

I am in the process of completing a short presentation on the properties of depleted uranium that make it so suited to it's use in modern munitions. I have stated that DU's high density means that a projectile made from it will have a much smaller cross sectional area than one made of steel, granting said projectile a greater penetrative force.

Now to my problem. I've spent a good hour scouring the net for a description/definition of what causes materials to have different densities on an atomic/molecular scale to no avail. I am aware that DU will have more atoms per given area than steel but I was hoping for significantly more detail?

Thanks in advance, Gordon.

 

[Mapes]

Hi TFGordon, welcome to PF!

Density depends on a number of factors, including bond length, atom size, and crystal structure. In the case of steel vs. uranium, the biggest factor is atom size: an atom of uranium has a lot more protons and neutrons than an atom of iron (the main constituent of steel).

 

[TFGordon]

Thanks awfully Mapes, but I was already aware that Uranium has 92 protons and 141-6 neutrons, significantly more than Iron. I may be sounding somewhat dim, I'm all too aware, but I was rather hoping there was more to it than that? Or am I just over-complicating this whole business?

Also, could you possibly shed some light on the pyrophoric qualities of uranium? (Is this a little naughty, asking a different question in the same thread? I'm willing to start a fresh one if the rules require.) Again, I know the basics; that uranium autoignites at around 500 celsius but what causes this? Is the 500 degree heat what is required to remove the initial electrons from a few of the U atoms, creating a cascade effect? Or is a wildly different process occurring?