Question

When an unstable nucleus produces an \(\alpha\) particle, by how many units does the atomic number of the nucleus change? Does the atomic number increase or decrease?

Short answer

When an unstable nucleus produces an alpha particle, its atomic number decreases by 2 units. This is because, during alpha emission, the nucleus loses two protons, which are part of the emitted alpha particle.

Step-by-step solution

Recall the properties of an alpha particle

An alpha particle is a type of ionizing radiation consisting of two protons and two neutrons, which can be seen as a helium nucleus (\(He^{2+}\)).

Understand the change in atomic number

The atomic number (Z) of an element indicates the number of protons in the nucleus. When an unstable nucleus emits an alpha particle, it loses two protons.

Determine the change in atomic number

Since an alpha emission involves the loss of two protons, the atomic number of the nucleus decreases by two units.

Summarize the result

When an unstable nucleus produces an alpha particle, its atomic number decreases by 2 units, meaning the nucleus now belongs to a different element with a lower atomic number.

Key concepts

Atomic Number Change

The atomic number, often symbolized as 'Z', is a fundamental characteristic of an element that represents the number of protons in an atomic nucleus.

During alpha particle emission, an atomic transformation takes place. This process is crucial in the realm of nuclear physics and chemistry as it alters an element's identity. An alpha particle, identical to a helium nucleus with a notation of (He^{2+}), comprises two protons and two neutrons. As it is emitted, the original unstable nucleus loses these two protons.

This ejection of an alpha particle results in a decrease in the atomic number of the original atom by two units. As a consequence, the identity of the atom changes because the atomic number is directly tied to the element's position in the periodic table. For instance, if Uranium-238 (^{238}_92U) emits an alpha particle, it transmutes into Thorium-234 (^{234}_90Th), moving two places to the left in the periodic table.

Properties of Alpha Particles

Alpha particles are a type of nuclear radiation that are relatively large and heavy, especially when compared to other forms of radioactive emissions such as beta particles or gamma rays.

Key properties of alpha particles include:

• Mass: An alpha particle has a mass of approximately 4 atomic mass units, comprising two protons and two neutrons.
• Charge: They carry a +2 electric charge due to the presence of two protons.
• Penetrating Power: They have low penetrating power and can be stopped by a sheet of paper or a few centimeters of air. This makes them less dangerous when encountered externally but they can cause significant damage to biological tissue when ingested or inhaled due to their high mass and charge.
• Ionizing Ability: Alpha particles are highly ionizing, which means they can knock electrons off atoms and molecules they encounter, creating ions.

These properties are important for understanding both the risks associated with alpha radiation and the precautions necessary for safely handling materials that emit alpha particles.

Nuclear Stability

An atomic nucleus is composed of protons and neutrons, whose numbers and ratios play a pivotal role in the stability of the nucleus. A stable nucleus will have an optimal proportion of protons to neutrons; any significant deviation can lead to radioactivity and the tendency of the nucleus to seek a more stable state.

Alpha particle emission is one of the paths a nucleus can take to achieve greater stability, particularly for heavy elements with high atomic numbers. Over time, these highly unstable nuclei will eject alpha particles, resulting in a lower atomic number and often a more stable configuration.

The concept of a 'decay series' is central to understanding these transformations—the sequential decay of radioactive elements, where each decay step moves closer to stability, often culminating in a non-radioactive isotope of lead. Moreover, the half-life of an element, the time taken for half of a given quantity of the substance to decay, is a key indicator of its stability. Shorter half-lives typically suggest a greater level of instability and thus a higher rate of alpha particle emission.