Now when it comes to the density of our transition metals, just remember that increases as the mass of the metal increases. We're going to say an increase in density down a group is more significant then across a period. And we're going to say here that the general trend is as we head from the left to the right side of our periodic table in relation to our transition metals, in this case our density is going to increase and that's because our mass is increasing.

And then we're going to say as we head down a group our mass also still increases. Now remember as we're heading across a group our size is staying relatively constant because we're just adding additional electrons to either our D or F orbitals. So our volume is staying more or less the same. d=mV. So your volume is staying more or less the same, but your mass is increasing. This causes an increase in your density.

If we're looking at going down a group, well, as we're going down a group, our mass is still increasing because we're going from lighter elements up top to heavier elements on the bottom. And then we have lanthanide contractions that are possible. So that kind of keeps your volume more or less close to the same as you're heading down a group. Again, your volume is staying relatively the same. Your mass is increasing greatly. This also causes an increase in your density.

So just remember the formula for density. Remember with our transition metals, because we're being in the same row or because of the lanthanide contraction, our volume is staying more or less the same, but our mass is increasing. This causes an overall increase in our density.