How Do Isotopes Work?

Isotopes are variations on the same chemical element that have different numbers of neutrons. Learn how these variants can behave differently -- and why chemists, physicists, and paleontologists are all interested in them -- in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of I Heart Radio. Hey,
brain Stuff, Laurin bobble bomb. Here. Atoms are the building
blocks of matter. Anything that has mass and occupies space
by having volume is made up of these we things
that goes for the air you breathe, the water you drink,
and your body itself. Isotopes are a vital concept in

(00:23):
the study of atoms and how they work. Chemists, physicists,
and geologists use them to make sense of our world.
But before we can explain what isotopes are or why
they're so important, we'll need to take a step back
and look at atoms as a whole. As you probably know,
atoms have three main components, two of which reside in
the atoms nucleus, located at the center of the atom.

(00:45):
The nucleus is a tightly packed cluster of particles. Some
of those particles are protons, which have positive electrical charges.
It's well documented that opposite charges attract, while similarly charged
bodies tend to repel one another. I think about the
ends of two magnets. So here's a question. How can
two or more protons with their positive charges come exist

(01:06):
in the same nucleus? Shouldn't they be pushing each other away.
That's where another type of particle comes in, neutrons. Neutrons
are subatomic particles that share nuclei with protons, but neutrons
don't possess an electrical charge. True to their name, neutrons
are neutral, being neither positively nor negatively charged. It's an
important attribute. By virtue of their neutrality, neutrons can stop

(01:30):
protons from driving one another clear out of the nucleus.
Orbiting the nucleus are the third main component of atoms, electrons,
which are ultra light particles with negative charges. Electrons facilitate
chemical bonding, and their movements can produce a little thing
called electricity. But protons are no less important for one thing,
they help scientists tell the elements apart. You might have

(01:53):
noticed that in most versions of the periodic table, each
square has a little number printed in its upper right
hand corner. That figure is known as the atomic number.
It tells the reader how many protons are in the
atomic nucleus of a given element. For example, Oxygen's atomic
number is eight. Every oxygen atom in the universe has
a nucleus with exactly eight protons, no more, no less.

(02:17):
Without this very specific arrangement of particles, oxygen wouldn't be oxygen.
Each elements atomic number, including oxygen's, is totally unique, and
it's a defining trait. No other element has eight protons
per nucleus. By counting the protons, you can identify an atom.
Just as oxygen atoms will always have eight protons, nitrogen
atoms invariably come with seven. It's that simple neutrons do

(02:41):
not follow suit the nucleus, and an oxygen atom is
guaranteed to harbor eight protons as we've established, However, it
might also contain anywhere from four to twenty neutrons. Isotopes
are variants of the same chemical element that have different
numbers of neutrons. Now, each isotope is named on the
basis its mass number, which is the total combined number

(03:02):
of neutrons and protons in an atom. For example, one
of the better known oxygen isotopes is called oxygen eighteen
because it's got the standard eight protons plus ten neutrons.
A related isotope, oxygen seventeen, has one fewer neutron in
the nucleus. Some combinations of subatomic particles are stronger than others.
Scientists classify oxygen seventeen and eighteen as stable isotopes. In

(03:27):
a stable isotope, the forces exerted by the protons and
neutrons hold each other together permanently, keeping the nucleus intact
on the flip side. The nuclei in radioactive isotopes, also
called radio isotopes, are unstable and will decay over time.
These things have a protons neutron ratio that's fundamentally unsustainable

(03:47):
in the long run. Nobody wants to stay in that predicament. Hence,
radioactive isotopes will shed some subatomic particles and release energy
while they're at it until they've converted themselves into nice
stable isotopes. So oxygen eighteen is stable, but oxygen nineteen
is not. The latter will inevitably break down and fast
within twenty six point eight eight seconds of its creation.

(04:10):
Any given sample of oxygen nineteen is guaranteed to lose
half of its atoms to the ravages of decay. That
means of oxygen nineteen has a half life of twenty
six point eight eight seconds. A half life is the
amount of time it takes of an isotope sample to decay.
Remember this concept, we're going to connect it to paleontology
in just a minute. But before we talk about fossil science,

(04:32):
there's an important point that needs to be made. Unlike oxygen,
some elements do not have any stable isotopes whatsoever. Consider
uranium in the natural world. There are three isotopes of
this heavy metal, and they're all radioactive. With the atomic
nuclei in a constant state of decay. Eventually a chunk
of uranium will turn into it altogether different element. Don't

(04:53):
bother trying to watch the transition in real time, though
the process unfolds very very slowly. Uranium two thirty eight,
the elements most common isotope, has a half life of
about four point five billion years. Gradually it will become
lead to OH six, which is stable. Likewise, uranium two
thirty five, with its seven hundred and four million year

(05:15):
half life, transitions into lead to OH seven, another stable isotope.
Two geologists, this is really useful information. Let's say somebody
finds a slab of rock whose zircon crystals contain a
mixture of uranium two thirty five and lead to OH seven.
The ratio of those two atoms can help scientists determine
the rocks age. Here's how Let's say the lead atoms

(05:38):
vastly outnumber their uranium counterparts. In that case, you know
you're looking at a pretty old rock. After all, the
uraniums had plenty of time to start transforming itself into lead.
On the other hand, if the opposite is true, and
the uranium atoms are more common, then the rock must
be on the younger side. The technique we've just described
is called radiometric dating. That's the act of using the

(06:00):
well documented decay rates of unstable isotopes to estimate the
age of rock samples and geologic formations. A Paleontologists have
harnessed the strategy to determine how much time has elapsed
since a particular fossil was deposited, though it's not always
possible to date the specimen directly. You don't need to
be a prehistory buff to appreciate isotopes. Medical practitioners use

(06:21):
some of the radioactive varieties to monitor blood flow, study
bone growth, and even fight cancer. Radio Isotopes have also
been used to give farmers insights into soil quality. So
there you have it. Something as seemingly abstract as the
variability of neutrons affects everything from cancer treatment to the
mysteries of deep time. Science is awesome. Today's episode was

(06:47):
written by Mark Mancini and produced by Tyler Clang. Brain
Stuff is a production of iHeart Radio's How Stuff Works.
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