Actinium and the Actinides

All 15 of these elements, (Atomic
numbers 89 - 103) all fit into the space
for Group 2, Period 7.  Rather than make
the table HUGE they are just pulled out
as a subgroup. All of the elements in this
group have such large
nuclei (the plural
of nucleus) that they are
radioactive
and will eventually break down into other
elements.  Elements 94 and higher are
all
man-made and are not found in
nature.