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Uranium
Uranium (symbol 'U') is a chemical element with atomic number 92, meaning it has 92 protons and electrons, including six valence electrons. Uranium, a silvery-grey metal in the actinide series, was discovered by Martin Heinrich Klaproth in 1789. It is weakly radioactive due to its unstable isotopes, with uranium-238 and uranium-235 being the most common. The mass number of uranium is 238.
1.0Introduction
Uranium is one of the most well-known and, arguably, infamous elements. Uranium is the heaviest naturally occurring element and is more abundant in the Earth's crust than silver. As an actinide, uranium belongs to large, heavy metals that fill their f-orbitals with valence electrons.
Chemically, uranium is intriguing due to its large nucleus, packed with protons and neutrons, which pulls its core electron shells inward, introducing relativistic effects that impact electron orbital energies.
Outside the lab, uranium is primarily known as a nuclear fuel, gaining attention in global discussions about nuclear energy's role in reducing carbon emissions. To power reactors, uranium—mostly U-238—is enriched with U-235, naturally occurring at only 0.7%.
2.0 Physical Properties of Uranium
- Solid at standard temperature and pressure with an orthorhombic crystal structure.
- Its slow radioactive decay generates heat, contributing to Earth's continental and convection drift.
- 18.7 times denser than water and among the heaviest naturally occurring elements by mass number.
- Used in aircraft counterweights and radiation shielding due to its high density.
- Malleable, ductile, slightly paramagnetic, strongly electropositive, and a poor conductor of electricity.
- Found naturally as a mixture of isotopes: U-238 (99.3%) and U-235 (0.7%).
- Silvery-grey in appearance, but corrodes to a black oxide in air.
3.0Chemical Properties of Uranium
- Uranium reacts with most nonmetals and their compounds, except noble gases.
- Its reactivity increases with temperature.
- It dissolves in hydrochloric and nitric acids but reacts slowly with non-oxidizing acids.
- Uranium is extracted from ores and converted into uranium dioxide or other usable forms in industrial processes.
- Finely divided uranium reacts with cold water.
- Uranium235 was the first fissile isotope discovered.
- When bombarded with slow neutrons, Uranium-235 splits into smaller nuclei, releasing nuclear binding energy and additional neutrons, essential for nuclear reactions.
4.0Uranium in Nuclear Energy
Uranium plays a critical role in generating electricity through nuclear fission. When uranium nuclei split, they release vast amounts of energy, rapidly converting to heat. In nuclear power plants, nuclear reactions generate heat, which turns water into steam, and drives turbines to generate electricity.
However, uranium ore must undergo extensive processing to become usable nuclear fuel. Yellowcake (U₃O₈) is the primary source of uranium, but only 0.7% of the uranium atoms in yellowcake are uranium-235, the isotope needed for reliable fission. To increase the concentration of uranium-235 to about 3%, the uranium oxide is converted to uranium hexafluoride (UF6), allowing for easier separation of the desired isotope through gaseous diffusion.
Nuclear energy has garnered interest in recent years as a solution to combat climate change since nuclear reactors, unlike fossil fuels, do not emit CO2 while producing electricity. However, concerns about safety, uranium availability, reactor efficiency, and costs continue to challenge the widespread adoption of nuclear energy as a solution.