Nuclear Chemistry

Nuclear Chemistry: definition

Let's start by looking at the definition of nuclear chemistry. Nuclear chemistry is the chemistry that deals with radioactivity, nuclear reactions and nuclear properties.

Nuclear reactions are reactions that involve an atom's nucleus. Since the nucleus is comprised of nucleons, which are protons and neutrons, we tend to ignore electrons as they are not a part of the nucleus.

Now, there are two ways to represent nuclides: atomic notation and mass notation. In atomic notation, the number on the top is the mass number, while the number on the bottom is the atomic number. In mass notation, the name of the element is followed by the mass number. For example, the atomic notation of an isotope of radium containing 140 neutrons is written as \( ^{228}_{88}\text{Ra} \), whereas its mass notation is radium-228,

• Mass number → number of protons plus the number of neutrons in the nucleus.
• Atomic number → proton number in the nucleus.

Figure 1. Atomic notation of radioactive isotope of radium, Isadora Santos - StudySmarter Originals.

History Of Nuclear Chemistry

Now, let's dive into the history of nuclear chemistry and learn about three different chemists that were important in the discovery of radioactivity.

First up, we have Wilhelm Röntgen, a German physicist. Röntgen was interested in understanding how a Crookes tube worked. The Crookes tube was a device created in 1870 by a British scientist named William Crookes. It consisted of a sealed glass cylinder, with no oxygen inside and two electrodes (an anode and a cathode). When there was a high voltage difference between both electrodes, a green/yellow glow would appear behind the anode, as if this light was being emitted from the cathode. Physicists called this invisible light "cathode rays".

However, in 1895, Röntgen discovered that there was another unknown radiation being emitted by the Crookes tube, besides the cathode rays. Well, it turns out he had just discovered X-rays!

Then, in 1896, Henri Becquerel enters the picture. Becquerel used the newly discovered X-rays to do some experimentation, and by accident, he stumbled upon the discovery of phosphorescent uranium salts that spontaneously emitted radiation! Becquerel had just discovered a new phenomenon: radioactivity!

Marie Curie was also a pioneer of radioactivity. In 1898, together with her husband Pierre Curie, Marie Curie discovered the elements polonium and radium. Marie was also the one who coined the term radioactivity.

Nuclear Chemistry Equations

The nuclear equations in nuclear chemistry involve special particles called nuclear particles, and the involvement of each of these nuclear particles depends on the type of nuclear decay happening to the nucleus of an unstable isotope.

• Unstable isotopes (Radioactive Isotopes) are those that have an unstable nucleus that can spontaneously undergo radioactive decay to form a stable isotope (daughter isotope).

Most importantly, in nuclear decay, a radioactive isotope with an unstable nucleus (also known as the parent isotope) undergoes spontaneous decomposition of its nucleus to form a daughter isotope with a stable nucleus!

There are six nuclear particles associated with nuclear equations. These are the neutron particle, proton particle, beta particle, alpha particle, and positron particle.

• The proton particle has the symbol \( ^{1}_{1} \text{p} \) and a charge of +1.
• The neutron particle has no charge and the symbol \(^{1}_{0} \text{n} \).
• The beta particle (or electron particle) has a charge of -1 and the symbol \(^{0}_{-1}\beta \) or \(^{0}_{-1} \text{e} \).
• The positron particle is the opposite of the beta particle, it was the symbol \(^{0}_{1}\beta \) and a +1 charge.
• The alpha particle has the symbol \( ^{4}_{2}\alpha \) and a charge of +2

When nuclear decay happens, these nuclear particles are either emitted or absorbed. Now, let's explore the different types of radioactive decay and the nuclear particles involved!

Beta Decay

Beta decay is probably the most common type of nuclear decay seen in nuclear reactions. In beta decay, an alpha particle (\(^{4}_{2}\alpha \)) is emitted, while the stable isotope loses one neutron and gains a proton.

For example, let's say that you have a radioactive isotope of carbon, carbon-14. The atomic notation for carbon-14 is \( ^{14}_6\text {C} \), meaning that has an atomic number of 6 and a mass number of 14.

Now, if you look for Carbon in your Periodic Table, you will find that the mass of carbon in the Periodic Table is 12. Since the mass number of carbon-14 is greater (14) than that mass number in the Periodic Table, carbon-14 will undergo beta decay.

$$ ^{14}_{6}\text{C }\longrightarrow \text{ }^{0}_{-1}\text{e + }^{14}_{7}\text{N} $$

Electron Capture and Positron Emission

Electron capture is basically the opposite of what we just saw in beta decay. During electron capture, a beta particle is absorbed instead of emitted.

During electron capture, an electron in an atom's inner shell is drawn into the nucleus where it combines with a proton, forming a neutron and a neutrino. The neutrino is ejected from the atom's nucleus. The nuclear equation below shows the electron capture in ¹⁹⁶Pb.

$$ ^{196}_{82}\text{Pb + } ^{0}_{-1}\text{e }\longrightarrow ^{196}_{81}\text{Tl + } \nu_{e} $$

Let's solve a problem!

Positron emission is a type of nuclear decay that can happen in isotopes with a mass smaller than that in the periodic table. In this case, a positron particle gets emitted, leading to the isotope gaining one neutron and losing one proton.

The nuclear equations for the positron emission in \( ^{26} \text{Al} \) is shown below:

$$ ^{26}_{13}\text{ Al }\to ^{0}_{1}\beta\text{ + }^{26}_{12}\text{ Mg } $$

Alpha Decay

The fourth type of nuclear decay is called alpha decay.

In this case, an alpha particle (\( ^{4}_{2}\alpha \)) gets emitted, and the resulting isotope will lose two protons and two neutrons (the equivalent of a helium nucleus!).

$$ ^{238}_{92}\text{U }\to \text{ }^{234}_{90}\text{Th + } ^{4}_{2} \alpha $$

Nuclear Chemistry Examples

Now that we know what nuclear chemistry encompasses and the different types of nuclear decay that can occur, let's look at some examples.

Plutonium-239 is a radioactive isotope of the element plutonium, and it is used in the generation of nuclear weapons. Since \( ^{239}_{94} \text {Pu}\) has an atomic number greater than 82 (94 > 82), its expected mode of decay is alpha decay.

$$ ^{239}_{94}\text{Pu }\to \text{ }^{235}_{92}\text{U + } ^{4}_{2} \alpha $$

Another example of an important radioactive isotope in nuclear chemistry is Fluorine-18. This isotope is important in positron emission tomography (PET), a type of imaging used to see the metabolic functions of tissues and organs. Fluorine-18 undergoes positron emission.

$$ ^{18}_{9}\text{ F }\to \text { } ^{0}_{1}\beta\text{ + }^{18}_{8}\text{O} $$

Applications of Nuclear Chemistry

To finish off, let's talk explore the applications of nuclear chemistry. Nuclear chemistry has very important medical applications, as some radioactive isotopes can be used for imaging, and also in the process of diagnosis and cancer treatment. Samarium-153, for instance, is a radioisotope used in the treatment of bone cancer.

The figure below shows some common isotopes used in the diagnosis and treatment of certain diseases.

Now, I hope that you feel ready to dive deep into nuclear chemistry!