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Uranium is a heavy metal with significant importance in the nuclear energy sector. It is represented by the symbol "U" and has an atomic number of 92. This means uranium has 92 protons in its nucleus, making it one of the heaviest naturally occurring elements.
Uranium is found in the form of several isotopes, with uranium-238 being the most abundant. However, uranium-235 is particularly noteworthy for its role in nuclear fission. Isotopes differ in mass numbers but have the same atomic number.
For nuclear applications, uranium is often enriched, which involves increasing the concentration of uranium-235 to enhance its ability to sustain a nuclear reaction.

Nuclear reactions involve changes to the nucleus of an atom. These transformations can release or absorb a lot of energy. One common type is neutron capture, which occurs when a neutron collides with and is absorbed by an atomic nucleus.
Nuclear reactions are distinct from chemical reactions; they change the identity of elements through alterations in the number of protons or neutrons in the nucleus. Such changes can lead to the formation of new isotopes or even completely different elements.

• In fission reactions, heavy nuclei, like uranium, split into smaller, lighter nuclei, releasing energy.
• Fusion reactions, on the other hand, involve light nuclei merging to form a heavier nucleus, also releasing energy.

The mass number is a crucial aspect of understanding elements and their isotopes. It is the total number of protons and neutrons in an atom's nucleus. It is represented by the upper number in isotopic notation, such as \( 248 \) in \\({ }_{92}^{248} \mathrm{U} \).
When a nucleus undergoes processes like neutron capture, it absorbs an additional neutron, leading to an increase in its mass number. This is because the nucleus now contains one extra neutron, making the nucleus heavier.
In our example, during neutron capture, uranium-248 becomes uranium-249, showcasing the increase in the mass number due to the addition of a neutron.

The atomic number is a fundamental characteristic of elements. It indicates the number of protons in an atom's nucleus and therefore determines the element's identity. Additionally, the atomic number dictates the placement of an element on the periodic table.
In isotopic notation, it is represented as the lower number, as seen in \({ }_{92}^{248} \mathrm{U} \),where "92" denotes uranium's atomic number. Regardless of changes in the mass number, as seen with neutron capture, the atomic number remains constant. Thus, the element's identity does not change.
This consistency means that even when uranium-248 absorbs a neutron and becomes uranium-249, the atomic number stays at 92, indicating that the element remains uranium.