why is osmium denser than gold?

[paul]

considering gold has a higher atomic number, and greater relative atomic mass (or is it "standard atomic weight"?) i would have thought gold to be the more dense?

[nitric]

osmium has a denser packed crystal lattice i believe, since it has a denser packed lattice then the density will be higher

[paul]

thanks nitric.

 

so, 1 atom of osmium is actually lense dense than 1 atom of gold?

 

but, where actual visible pieces of the metals are concerned, osmium is more dense than gold?

[Sisyphus]

I don't think it really makes much sense to talk about the density of a single atom, since it's size is pretty indefinite. (You can talk about mass, though.) Density in general is also always conditional. Osmium has the highest density in normal solid state under normal pressure, because it's both heavy and packs relatively tightly together. In gaseous form (which for stuff like osmium and gold I imagine means the kind of heat you usually only find in stars), density is almost directly proportional to molecular mass. In liquid form, it's probably something else.

[nitric]

i agree, density is conditional base on many factors, and density of an atom is impossible, density is the measure of how much matter is packed into one place

[farmboy]

As others have pointed out, it isn't really the nucleus that is important, but the way the atoms are arranged in their lattice. Osmium adopts a hexagonal close packed lattice structure which has a higher packing efficency (90.69%) than golds face centred cubic lattice structure (74.05%).

[John Cuthber]

I can only think of one way of looking at the density of individual atoms, and that's as monatomic vapours. At some high enough temperature and low enough pressure both gold and osmium would be vapours. The gas laws say that the gas with the higher atomic weight (gold in this case) is denser.

[DrP]

This is a classic example of why Lead is so light! (Yes.. light). Every one thinks of lead being 'Heavy' and dense (because it it is compared to some metals) but its weigt is ALL to do with it's RMM (Atomic number 82?). Really, one would expect Lead to be MUCH denser and heavier per per unit volume than it actually is. Again, this is due to the packing structure of the atoms. With lead it is Body Centred Cubic - which id not a very close packed structure at all. (9 atoms per cube - one on each corner and one in the centre). If it were Face Centred Cubic (14 atoms - one on each corner and one in the middle of each face) it would be much heavier per unit volume. Even more so with Hexagonal Close Packing - which is asdense as you get (imagine balls layed out in a box packed as tightly as they can get - they form hexagons).