Video Transcript
Which of the following statements
about spontaneous changes to the compositions of atomic nuclei of elements is
correct? The composition of an atomic
nucleus can spontaneously change only for atoms of certain elements. The composition of an atomic
nucleus can spontaneously change for atoms of any element. The composition of an atomic
nucleus cannot spontaneously change for atoms of any element.
To answer the question correctly,
we must ensure that we understand two things: what “change of the composition of an
atomic nucleus” means in the question and what “spontaneously change” means in the
question.
A change of composition of an
atomic nucleus means a change to what the nucleus is made of. That could be adding something to
the nucleus or removing something from the nucleus. The meaning of “spontaneously
change” in the question is change without any influence from any other object. If something is added to a nucleus,
whatever was added must have come from outside the nucleus. Anything that comes from outside
the nucleus that changes the composition of the nucleus would not be a spontaneous
change to the nucleus. We see then that we can only
consider removal of things from a nucleus as changes that could be spontaneous.
Recall that when nuclear radiation
is emitted by a nucleus, something must actually leave the nucleus. Nuclear radiation is something. And whatever this something is, it
must have been in a nucleus before being emitted by that nucleus. We see then that we can determine
whether nuclei of atoms of an element can undergo spontaneous nuclear decay by
checking if these atoms emit nuclear radiation without us doing anything to
influence them to emit this radiation.
Now, we know that naturally
occurring nuclear radiation sources exist, as we know that nuclear radiation can
come from space and from rocks in the Earth. This tells us that at least some
elements must have atoms with nuclei that spontaneously emit nuclear radiation. These nuclei must spontaneously
decay. We reject option (C), as option (C)
says that there are no elements that have atoms with spontaneously decaying
nuclei.
Do all elements have atoms with
nuclei that spontaneously decay though? No, they do not. Some elements are stable. Atoms of these elements have nuclei
that will not spontaneously decay. We reject option (B).
We accept option (A) then. Some elements have atoms with
nuclei that can spontaneously change composition.
