Nuclear Chemistry: Crash Course Chemistry #38

Summary

This Crash Course Chemistry episode delves into radioactivity, a misunderstood yet fascinating aspect of nuclear chemistry. It explains how radioactivity isn't a typical chemical reaction but involves changes in an atom's nucleus, leading to transmutation. The video introduces different types of radioactive decay—alpha, beta, and gamma—and spontaneous fission, emphasizing their distinct characteristics and potential impacts, such as DNA mutations and cancer. It also touches on how half-life calculations are crucial for understanding radioactive decay rates.

Takeaways

• ⚛ Radioactivity is a prominent yet misunderstood concept in popular culture, often associated with both superpowers and catastrophic effects.
• 🔬 Radioactivity is more related to nuclear chemistry than traditional chemistry, as it involves changes in the atomic nucleus, not just electron transfers.
• 🌟 The transformation of one element into another, or one isotope to another, is known as transmutation, which can theoretically turn lead into gold, albeit impractically.
• 🔋 Nuclear reactions can release vast amounts of energy, much more than traditional chemical reactions, making them a potential power source.
• ⚠️ Radioactive decay is a natural process where an unstable nucleus seeks stability by releasing particles or energy, resulting in a different element or isotope.
• 🕰 The half-life of a radioactive isotope is a key concept, indicating the time required for half of a sample to decay, and is crucial for understanding decay rates.
• 📉 There are three main types of radioactive decay: alpha decay (release of helium nuclei), beta decay (release of electrons), and gamma decay (release of high-energy photons).
• 🛡 Alpha particles can be stopped by a sheet of paper or cloth, beta particles by aluminum foil or skin, but gamma rays can penetrate deeply and are the most dangerous.
• 🌐 Radioactive isotopes are part of a decay chain originating from supernovae, and some, like carbon-14, are continuously renewed by cosmic rays, ensuring their presence on Earth.
• 🔄 Spontaneous fission is a rare form of radioactivity where an atom splits into two smaller atoms without external influence, significant for producing neutrons for nuclear reactions.

Q & A

What is radioactivity, and why is it often misunderstood?

Radioactivity refers to the release of energy from the decay of unstable atomic nuclei. It's often misunderstood because popular media portrays it as primarily harmful, mutating genes or melting skin, when in reality, not all forms of radioactivity are dangerous. Some forms, like alpha and beta radiation, can be easily stopped, while others, like gamma radiation, are more hazardous.

How is radioactivity related to nuclear chemistry?

While traditional chemistry involves the interaction of outermost electrons, nuclear chemistry focuses on changes within the nucleus, involving protons and neutrons. When these particles are altered, it can release much larger amounts of energy compared to regular chemical reactions.

What is transmutation, and how is it significant in nuclear reactions?

Transmutation is the process by which one element changes into another due to changes in its number of protons or neutrons. It's significant because it shows how nuclear reactions can alter the fundamental nature of an element, like turning lead into gold, though the process is expensive and impractical for most purposes.

Why are some radioactive elements still present on Earth if they eventually decay into stable forms?

Radioactive elements persist because they are part of long decay chains. Elements with longer half-lives decay into other radioactive forms, keeping them around for billions of years. Additionally, some elements, like carbon-14, are constantly replenished by cosmic rays.

What are the three types of radioactive decay, and how do they differ?

The three types are alpha decay, beta decay, and gamma decay. Alpha decay releases a helium nucleus (2 protons, 2 neutrons), beta decay emits electrons or positrons, and gamma decay emits electromagnetic radiation (energy) without releasing particles.

What is half-life, and why is it important in nuclear chemistry?

Half-life is the time it takes for half of a radioactive sample to decay into a more stable form. It's important because it helps scientists determine how long a radioactive element will remain active and how much of it will remain after a given period.

What are the dangers associated with gamma radiation?

Gamma radiation is dangerous because it has high energy and can penetrate deep into human tissue, potentially damaging cells and DNA. This can lead to burns, radiation sickness, mutations, and an increased risk of cancer.

How does alpha radiation compare to other types of radiation in terms of energy and danger?

Alpha radiation has relatively low energy compared to beta and gamma radiation. It can be stopped by a sheet of paper or even skin, making it less dangerous externally. However, if inhaled or ingested, alpha particles can cause significant internal damage.

What role does spontaneous fission play in nuclear chemistry?

Spontaneous fission is when an atom splits into two smaller atoms without external influence. It's rare in most elements but useful in materials like Californium-254, which can produce neutrons used in other nuclear reactions.

What is gamma decay, and when does it typically occur?

Gamma decay occurs when an excited nucleus releases excess energy in the form of gamma radiation, often accompanying other forms of radioactive decay like alpha or beta decay. It involves no change in the number of protons or neutrons, only energy release.

Outlines

00:00

🔬 Radioactivity: The Misunderstood Marvel

This paragraph delves into the popular yet misunderstood concept of radioactivity. Often portrayed as a plot device in sci-fi movies, radioactivity is a principle of chemistry that is both feared and fascinating due to its potential to mutate genes or even melt faces. However, it also holds the key to producing electricity without contributing to global warming, as exemplified by nuclear power plants. The script introduces the audience to the basics of nuclear chemistry, explaining that while chemical reactions typically involve electron transfers, nuclear reactions involve changes in the atomic nucleus, releasing vast amounts of energy. The concept of transmutation, where one element or isotope is changed into another, is introduced, along with the idea that atoms seek stability, just like humans do. Radioactive decay, a process where an unstable nucleus decomposes to form a more stable one, is also discussed, with the half-life concept explained using phosphorus-32 as an example. The paragraph concludes with a teaser for the next episode, which will explore nuclear fission and fusion.

05:01

🌟 Types of Radioactive Decay: Unraveling the Atom's Secrets

This paragraph explores the different types of radioactive decay, each characterized by the particles or energy released from the nucleus. The most common form of uranium, uranium-238, is used as an example to explain alpha decay, which releases an alpha particle consisting of two protons and two neutrons, effectively transforming uranium into thorium-234. Beta decay, which involves the emission of electrons, is introduced as the next type of decay, with thorium-234 decaying into xenon while releasing an electron. The script then describes gamma decay, which emits electromagnetic radiation without any particles, and is often associated with transitions of electrons from excited to ground states. Spontaneous fission, a rare occurrence where an atom splits into two smaller atoms without external influence, is also mentioned, with Californium-254 highlighted as a notable exception due to its practical use in producing neutrons. The paragraph wraps up by emphasizing the potential dangers of gamma radiation, which can penetrate deeply into tissues and cause significant harm, including DNA mutations and cancer.

Keywords

💡Radioactivity

Radioactivity refers to the spontaneous decay of atomic nuclei, resulting in the emission of particles or electromagnetic radiation. In the video, radioactivity is portrayed as a misunderstood yet fascinating aspect of nuclear chemistry that has been a plot device in many sci-fi movies. The script explains that while radioactivity can be harmful, it also has the potential to produce electricity without contributing to global warming, as mentioned in the context of nuclear power.

💡Nuclear Chemistry

Nuclear chemistry is the study of the changes that occur in the nucleus of an atom, involving protons and neutrons. Unlike chemical reactions that involve electron transfer, nuclear reactions release far more energy. The video emphasizes that nuclear chemistry is responsible for phenomena like transmutation, where one element can be changed into another, and is distinct from traditional chemistry.

💡Transmutation

Transmutation is the process of changing one element into another or one isotope into another. The video uses the example of alchemy, where lead could be turned into gold, to illustrate the concept. It's noted that while transmutation is possible, it is often not practical due to the high costs involved, as in the case of turning lead into gold.

💡Isotopes

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. The video explains that changes in the number of neutrons can create different isotopes, which is a form of transmutation. Isotopes are a key concept in understanding nuclear reactions and their applications.

💡Half-life

The half-life of a radioactive isotope is the time it takes for half of a sample to decay. The video uses phosphorus-32 as an example, explaining that its half-life is 14.3 days, meaning that after two weeks, half of the sample would have decayed. Half-life is a critical concept for understanding the rate of radioactive decay and the time scales involved.

💡Alpha Decay

Alpha decay is a type of radioactive decay where an atom's nucleus emits an alpha particle, which consists of two protons and two neutrons. The video explains that this process transforms uranium-238 into thorium-234, and it's characterized by the release of a helium nucleus. Alpha particles are relatively low energy and can be stopped by a sheet of paper or cloth.

💡Beta Decay

Beta decay is another form of radioactive decay where an atom's nucleus emits an electron or a positron. The video describes how thorium-234, formed from uranium-238 through alpha decay, can undergo beta decay, emitting an electron and transforming into xenon. Beta particles have higher energy than alpha particles and can be stopped by aluminum foil or the outer layers of human skin.

💡Gamma Decay

Gamma decay involves the emission of gamma rays, which are high-energy electromagnetic radiation. Unlike alpha and beta decay, gamma decay does not involve the emission of particles but rather energy. The video explains that gamma rays can be harmful as they can penetrate skin and cell membranes, potentially causing DNA mutations and cancer.

💡Spontaneous Fission

Spontaneous fission is a rare type of radioactive decay where an atomic nucleus splits into two smaller nuclei without external assistance. The video mentions that Californium-254 is an example of an element that undergoes spontaneous fission at a rate useful for producing neutrons for other nuclear reactions.

💡Ionizing Radiation

Ionizing radiation is a term used to describe radiation that carries enough energy to ionize atoms or molecules by removing tightly bound electrons. The video explains that radioactive decay typically results in ionizing radiation, which can be in the form of alpha, beta, or gamma rays, and has the potential to cause damage to living organisms by altering DNA.

Highlights

Radioactivity can be misunderstood as only causing mutations or harmful effects, but it has diverse applications, including electricity generation.

Nuclear chemistry is different from traditional chemistry because it involves changes in the nucleus, releasing much more energy than typical chemical reactions.

Transmutation involves changing one element into another, which is theoretically possible but highly expensive.

Atoms aim for stability, and when they are unstable due to improper proton or neutron ratios, they undergo radioactive decay.

The concept of half-life allows us to calculate how long it takes for half of a radioactive substance to decay.

Radioactive elements persist because of long decay chains that last billions of years, originating from elements formed in supernovas.

There are three types of radioactive decay: alpha, beta, and gamma, each with different properties and effects.

Alpha decay releases an alpha particle, which is the equivalent of a helium nucleus and can be stopped by paper or cloth.

Beta decay releases electrons and can be stopped by aluminum foil or skin.

Gamma decay emits electromagnetic radiation, which is highly penetrating and can damage cells, causing mutations or cancer.

Gamma radiation is one of the most dangerous forms of radiation as it can penetrate skin and alter DNA.

Spontaneous fission occurs when an atom splits into two smaller atoms without external influence, but this is rare and slow.

Californium-254 is one of the few elements that undergo spontaneous fission at a useful rate, often used to produce neutrons.

Radioactivity can be harnessed for beneficial purposes, such as energy generation and scientific experiments.

Understanding the types of radiation (alpha, beta, gamma) and their effects helps demystify the misconceptions surrounding nuclear chemistry.

Transcripts

Apparently, it can turn you into a superhero or into a mutant zombie.

It's the plot device for probably half of the sci-fi movies made in the last 60 years

and it's even the name of the song that welcomes you to the new age, to the new age, welcome to the new age.

Presumably this new age occurring after some kind of apocalypse.

As principles of chemistry go, few figure more prominently in the popular imagination than radioactivity,

but at the same time few are as completely misunderstood.

Most people think of radioactivity as just some thing that mutates genes and melts faces off.

And yes, some forms of radioactivity can do those things.

But all the more reason to understand it, right?

And also we can harness it to produce lots of electricity to fuel our rock and roll lifestyles without contributing to global warming,

though as Fukushima has taught us it comes with some of its own problems,

which we'll explore more next episode.

Before we get into the nuts and bolts of nuclear chemistry,

like nuclear fission and why it's so awesome as well as fusion and why it's so hard to do,

we'll first get to know radioactivity.

What it is, what different kinds there are, and why you don't really need to fear it.

At least, you know, not all the time.

[Theme Music]

So, radioactivity doesn't actually have a lot to do with chemistry in the sense that

we've been talking about for most of this course.

Chemical reactions happen when an atom's outermost electrons do stuff,

and the protons and neutrons and even the inner electron shells are usually completely unaffected.

But the protons and neutrons are still part of the atom, of course, still part of the chemicals,

and their interactions are important.

When protons and neutrons get directly involved in reactions and their numbers do change,

huge amounts of energy can be released.

Far more than by the transfer of electrons that we've learnted about in other reactions.

When these changes happen to the nucleus of an atom we rather logically call their study: Nuclear Chemistry.

Now it's probably occurred to you already that changing the nucleus of an atom can completely change it's nature.

Protons are the key to an atom's identity

so any change that affects the number of protons will turn one element into a completely different one.

An alchemist's dream, right? Lead to gold.

So as you might expect, that's not something that usually happens in a typical chemical reaction.

The same can be said of that other component of the nucleus, neutrons.

Atoms of the same element that have the same number of protons, but different numbers of neutrons are isotopes.

So changes in the number of neutrons in an atom create different isotopes of the same element.

Both of these kinds of changes, changing one element to another,

or changing one isotope to another are known as transmutation.

And it is, indeed, possible to transmute lead to gold.

Its just so ridiculously expensive that the tiny amounts of gold produced could never pay for the process.

But the very fact that it is possible, should clue you in that nuclear chemistry is an entirely different flavor of chemistry sauce.

Though, as with non nuclear chemistry, the changes that take place in a nuclear reaction

all come down to the atom's desire to have what we all want in life, stability.

Just as atoms are most stable when their outermost electron orbitals are full of electrons,

certain combinations of protons and neutrons make the nucleus more stable.

And just like when an atom gains or loses or shares electrons to stabilize it's outer shell,

when the numbers of protons or neutrons aren't ideal,

the nucleus releases some of them to try to reach a stable configuration.

When a nucleus decomposes in this way to form a different nucleus that's radioactive decay.

And just like with other chemical reactions we've talked about,

we need to know more about a nuclear reaction than just what's reacting and what's being produced.

Probably the most important thing to learn is how much of the product is being made and how fast.

Now you've heard of half life, it's the measurement that tells us just that.

The time it takes for exactly one half of the sample to decay.

Different nuclei have different half lives.

By knowing the half life, we can calculate how much of a sample will be gone in a given amount of time.

For example, the half life of phosphorus-32 is 14.3 days.

So if you start with a 100 gram sample, after about 2 weeks you'll have 50 grams left.

After another 2 weeks, half of the remainder would decay leaving only 25 grams of undecayed phosphorus, and so on.

Now you might be asking, if radioactive elements are always decaying in to more and more stable isotopes

that are eventually no longer radioactive, why are they still around at all?

Fascinating question, you seem to have brought your clever pants today.

Well it's fairly simple, given enough time all radioactive elements would decay in to non radioactive forms.

Even ultra stable bismuth, with it's half life longer than the age of the universe.

But elements with short half lives are around because they were decayed in to by elements that recently decayed in to them.

The chain of decay from the element originally produced in whatever supernova created them,

to the elements that exist on Earth now last billions and billions of years.

Also, I should note that some radioactive isotopes like carbon-14 in the atmosphere

are constantly being renewed by cosmic rays.

Now radioactive decay occurs when a nucleus has a higher energy level than a potentially more stable version.

Typically this difference in energy is released as what's called ionizing radiation.

Which you know as radioactivity.

It's ionizing because it has enough energy to knock electrons out or add electrons to other atoms.

Essentially creating ions.

There are three general types of radioactive decay,

each named for exactly what is released from the nucleus as it decays.

Let's take a look at what may be the most famous radioactive element, uranium.

By far the most common naturally occurring form of uranium is the isotope uranium-238.

More than 99% of the natural uranium in the world is in this form.

U-238 spontaneously decays in to thorium-234, in a process that releases something called an alpha particle.

This is called alpha decay and the particle that it emits is basically the same as a helium nucleus:

two protons and two neutrons.

We even describe it that way when writing it.

So right away you can see that the math checks out when it comes to the protons and neutrons.

92 minus 2, is 90. And 238 minus 4, leaves you with 234.

But you'll note, that we don't write the charges.

The helium nucleus obviously has a plus 2 charge, and the thorium atom would have a negative charge as well.

While its not incorrect to write them,

these charges are often omitted to emphasize what's going on in the nucleus.

Now alpha particles have relatively low energy, they're pretty heavy as particles go.

So while I try not to make a habit of walking around with a hunk of uranium in my pocket,

alpha particles can be stopped by nothing more than a sheet of paper or cloth.

The second type of radioactive decay is beta decay, which simply emits electrons.

It has somewhat higher energy than alpha radiation,

but it can still be stopped by a sheet of aluminum foil or the top layers of your skin.

So that thorium-234 that formed when uranium underwent alpha decay?

It can continue to decay on its own, and when it does it undergoes beta decay.

Releasing an electron and an atom of xenon.

Notice that again, the way we write this is a little different.

Even though the thorium emits an electron we don't use the usual symbol for electrons.

Instead we write it in nuclear notation form, with the mass number at top and the atomic number at the bottom.

Since its an electron, and not a proton, we put a negative 1 for the atomic number.

That probably seems a little weird right now,

but next week when we talk about nuclear equations, you will see why it's useful.

The third type of decay, is a little different, because it only emits energy, not a particle.

Its called gamma decay, and it releases electromagnetic radiation similar to visible light,

or UV radiation, but higher on the energy scale.

Because it's just energy, gamma radiation has no mass and contains no protons, neutrons, or electrons.

So it's written with two zeros.

This form of radiation is often released when electrons transition from an unstable excited state,

to a more stable state that has a lower energy. That's called the ground state.

Depending on how much energy the electron loses, the extra energy can be released in the form of visible,

or ultraviolet light, x-rays, or gamma waves.

Let's take the example of nickle-60.

Imagine there's an atom of nickle-60 with one or more of its electrons in an excited state.

That's what the little asterisks designates.

Atoms can get to this state when they are themselves the products of radioactive decay,

or if they get bombarded with radiation from other reactions pushing their electrons in to a higher energy level.

Now when all those electrons drop down to the ground state,

that atom is going to release some gamma radiation.

This kind of transition can also take place where other kinds of nuclear reactions are going on.

So gamma decay often occurs along with some other form of decay too.

So for example, if that uranium atom is at an excited state when it decays in to thorium,

it can simultaneous release gamma waves as well as the alpha particle I already mentioned.

Now you might have heard of gamma radiation more than the other kinds I've mentioned

because it can actually do some serious harm.

Like potentially turning you in to a giant green rage monster

that doesn't obey the laws of conservation of matter.

Unlike the particles emitted by other kinds of radiation, gamma rays can penetrate your skin,

your cell membranes, and ultimately the organelles within your cells.

So gamma radiation can not only cause skin burns, nausea,

other symptoms we associate with radiation poisoning,

it can also alter your DNA causing mutations and cancer.

OK, but to turn the frown upside down.

There's one more type of radioactivity that I'm happy to say is really simple.

It's called spontaneous fission and it occurs when an atom simply breaks in to 2 smaller atoms without any outside help.

This occurs at a ridiculously slow rate in most cases.

In fact, the only substances that does it at a rate that sufficient to serve any purposes is Californium-254.

And that purpose is to produce neutrons for use in other nuclear reactions.

But we'll talk more about that when we go in to fission, fusion,

and how scientists use and control nuclear reactions.

In the meantime, thank you for watching this episode of Crash Course Chemistry.

If you listened carefully, you learned what radioactivity really is.

And about transmutation among elements and among isotopes.

And how to make calculations based on an elements half life.

You also learned about different types of radioactive decay: alpha, beta, and gamma.

And about spontaneous fission.

This episode was written by Edi González and Blake de Pastino.

It was edited by Blake de Pastino. And our chemistry consultant is Dr. Heiko Langner.

It was filmed, edited, and directed by Nicholas Jenkins.

The script supervisor was Michael Aranda, who is also our sound designer.

And our graphics team is Thought Café.