1. Nuclear Chemistry
2 major topics:
Radioactive decay
Fission and Fusion

2. Radioactive Decay
Certain isotopes of certain elements, such as Uranium-235, have unstable nuclei. These are called radioactive isotopes; given some time, these unstable nuclei will undergo radioactive decay to give off energy and become more stable. There are many kinds of radioactive decay, but for this class we’ll only look at three major ones:
Alpha () decay
Beta (β) decay
Gamma (γ) decay
Sometimes, nuclei might still be radioactive after these processes, so multiple decays may occur in a sequence.

3. Alpha decay
In alpha decay, the radioactive isotope ejects an alpha particle from its nucleus. An alpha particle has two protons and two neutrons. It has no electrons, so it has a 2+ charge. Because an alpha particle is technically a helium ion in a specific situation, you might see alpha particles labeled like this: 2 4 𝐻𝑒 (The charge is usually not shown here for some reason)
Because the nucleus loses two protons and two electrons, the element actually changes. For example, if bismuth-210 (atomic number 83) undergoes alpha decay, it becomes thallium-206 (atomic number 81).

4. Beta decay
There are several types of beta decay, but the one we will focus on is the ejecting of an electron. In this kind of beta decay, one neutron in the nucleus of the radioactive element will turn into a proton. This conversion releases an electron, which is ejected from the nucleus. Note that this process has nothing to do with the electrons in the atom’s electron cloud.
Because a neutron turns into a proton, the element once again changes. For example, if calcium-48 (atomic number 20) undergoes beta decay, it becomes scandium-48 (atomic number 21).

5. Gamma Decay
When a particle undergoes gamma decay, there are no changes to its nucleus. The nucleus simply emits gamma radiation, a kind of electromagnetic wave. (Light is also a form of electromagnetic radiation, but gamma waves are beyond the visible spectrum.) Like the other kinds of decay, this process gives off energy (exothermic) and makes the nucleus more stable.

6. Half-lives
The time it takes for any one atom to undergo decay is random, but for large samples of radioactive isotopes, a trend can be observed about the rate of decay. The amount of atoms that have yet to decay can always be modeled by a function of exponential decay.
According to this model, the amount of remaining radioactive material never completely disappears, but gets halved at regular intervals. The amount of time it takes for half of a sample of a radioactive isotope to decay is called its half-life. The half life of a decay process depends on the element that’s decaying and can be anywhere from a tiny fraction of a second to billions of years (or more).
Useful formula: 𝐴 𝑓 = 𝐴 𝑖 ( 1 2 ) 𝑛 where n is the number of half lives that occur. Understand why this formula works.

7. Fission and Fusion
Fission is the splitting of the nucleus of an atom into two nuclei with lower atomic mass
Fusion is the combination of two nuclei into one nucleus with higher atomic mass

8. Fission Applications
Nuclear power: Fission is used in nuclear power plants. When certain elements are split, a tremendous amount of heat energy is released. This heat boils water to spin the blades of a turbine to generate lots of electricity. Nuclear power is very efficient and doesn’t produce greenhouse gases like the combustion of fossil fuels does, but it does produce long-lasting radioactive waste and can be dangerous.
Nuclear weapons: In nuclear weapons, elements are also split to release lots of energy, but unlike in nuclear reactors, this energy is not contained. Often in this situation, the fission of one atom results in the fission of several more atoms, which each result in even more fission, causing a chain reaction.

9. Chain Reaction
Each time uranium-235 fission takes place, neutrons are ejected with a lot of energy. When these hit the nuclei of other uranium-235 atoms, these also undergo fission, ejecting more neutrons, etc.

10. Fusion Applications
The sun consists of continuous fusion reactions of hydrogen combining to form helium and heavier elements. Though scientists have used fusion to create several new elements, they have not managed to perform the kind of fusion the sun uses- a sustainable reaction that releases huge amounts of energy (far more even than fission). Though no one is sure whether a fission reactor could be possible, it is the subject of much research; if fission reactors could be built, they could provide completely clean energy to entire countries.