# How to reason in terms of atomic radius in this case?

I am trying to solve a pset from MIT $$5.111$$ class. The question is which of vanadium and molybdenium has the largest radius. The right answer (given in the pset answers) is: molybdenum.

In class, we have only seen that the radius across a period gets smaller, and across a column gets bigger.

However, this knowledge doesn't allow us to conclude (because $$r_V > r_{Cr}$$ but $$r_{Cr} < r_{Mo}$$).

What kind of reasoning allows us to conclude ?

• Why not obscure your question even more? I don't care whatever "pset from MIT 5.111 class" is. You need to actually write a question. Not necessarily in original form, but asking why radius of Mo is bigger then Cr in title, would tell whatever the thing is about. Commented Jun 21 at 11:27

• Therefore, it can be assumed from these patterns that $$(r_\ce{Mo} - r_\ce{Cr}) \gt (r_\ce{V} - r_\ce{Cr})$$ and therefore $$r_\ce{Mo} \gt r_\ce{V}$$.
• OTOH, due the lanthanide contraction, the differences of the radius (and of chemical properties) are much smaller between the periods 5 and 6, therefore there can be implied that $$r_\ce{W} \lt r_\ce{Nb}$$ as $$r_\ce{W} - r_\ce{Mo} \lt r_\ce{Nb} - r_\ce{Mo}$$.