# Why is arsenic more chemically similar to phosphorus than is nitrogen?

Why is arsenic more chemically similar to phosphorus than is nitrogen (to phosphorus)?

I thought that it may be because both phosphorus and arsenic have d orbitals (albeit one has one that is filled and the other has an unfilled one).

Another possibility I thought was that because nitrogen held the electrons very closely, and thus the difference between the second and third period may be more pronounced than the difference between the third and fourth periods.

I'd really appreciate it if anyone could help clarify/ explain. Thanks!

• @NicolauSakerNeto Indeed, the $4d$ transition metals are rather similar to the $5d$, but considerably different from the $3d$; and there are stark differences between the lanthanides ($4f$) and actinides ($5f$). Thank you for the reference, I will be reading it promptly! – hBy2Py Sep 9 '15 at 1:48