Video Transcript
When an atomic nucleus emits a
gamma ray, by how much does the atomic number of the nucleus change?
Okay, so in this example, we have
an atomic nucleus. Let’s say that this is it. And we’re told this nucleus emits a
gamma ray. And we can symbolize that this
way. When a nucleus emits a gamma ray,
we say that it’s giving off gamma radiation. Now, an important thing to realize
about gamma radiation is that it’s purely energy. There’s no mass involved. Another way to describe a gamma ray
is as a packet of electromagnetic radiation called a photon. Now, if a gamma ray has no mass,
that also means it has no protons or electrons in it because those objects have a
mass. So, our massless gamma ray also has
no electric charge. And this fact helps us answer our
question of how much the atomic number of this nucleus that gives off the gamma ray
changes.
The atomic number — we can call it
𝑧 — of an element is equal to the number of protons in the nucleus. Since the relative charge of a
single proton is plus one, the number of protons in a nucleus and its overall
relative charge are the same. Just as a side note, when it comes
to other subatomic masses such as beta particles, which are electrons, this
similarity between proton number and relative charge means that, often, an emitted
electron is symbolized as having an atomic number of negative one. This doesn’t mean that a beta
particle has negative-one protons, but rather that its relative charge is negative
one.
All this to say that when we’re
talking about atomic nuclei, atomic number corresponds to the relative charge of the
nucleus. And as we saw earlier, the relative
charge of a gamma ray is zero because there’s no charge or mass involved in this
radiation. That means it has no effect on the
atomic number of the nucleus from which it was emitted. So, when we talk about how much the
atomic number of that nucleus changes, the answer is simply that it doesn’t change
at all. The change is zero. Another way to say this is that the
atomic number of a nucleus that emits a gamma ray stays the same.
