Problem 13 - Chemistry The Molecular Science

Question

By what processes do these transformations occur? (a) Uranium-238 to thorium-234 (b) Iodine-131 to xenon-131 (c) Nitrogen- 13 to carbon- 13 (d) Bismuth-214 to polonium-214

Step-by-Step Solution

Answer

(a) Alpha decay, (b) Beta decay, (c) Positron emission, (d) Beta decay.

Step 1: Identify the Nuclear Process for Uranium-238 to Thorium-234

Uranium-238 (\[^{238}_{92}\text{U}\]) transforms into Thorium-234 (\[^{234}_{90}\text{Th}\]) through a process known as alpha decay. An alpha particle, which consists of 2 protons and 2 neutrons (\[^{4}_{2}\text{He}\]), is emitted. This reduces the atomic number by 2 and the mass number by 4.

Step 2: Identify the Nuclear Process for Iodine-131 to Xenon-131

Iodine-131 (\[^{131}_{53}\text{I}\]) transforms into Xenon-131 (\[^{131}_{54}\text{Xe}\]) through beta decay. In beta decay, a neutron in the nucleus is converted into a proton, and a beta particle (electron, \[e^-\]) is emitted, resulting in an increase in the atomic number by 1, but the mass number remains unchanged.

Step 3: Identify the Nuclear Process for Nitrogen-13 to Carbon-13

Nitrogen-13 (\[^{13}_{7}\text{N}\]) transforms into Carbon-13 (\[^{13}_{6}\text{C}\]) through positron emission or positive beta decay. Here, a proton is converted into a neutron, and a positron (\[e^+\], the antimatter equivalent of an electron) is emitted. This decreases the atomic number by 1, but the mass number stays the same.

Step 4: Identify the Nuclear Process for Bismuth-214 to Polonium-214

Bismuth-214 (\[^{214}_{83}\text{Bi}\]) transforms into Polonium-214 (\[^{214}_{84}\text{Po}\]) through beta decay. During this process, a neutron is transformed into a proton, emitting a beta particle (electron), and thereby increasing the atomic number by 1, but the mass number remains unchanged.

Key Concepts

Alpha Decay

Alpha decay is a type of radioactive decay where an unstable nucleus releases an alpha particle. An alpha particle is made up of 2 protons and 2 neutrons, essentially a helium-4 nucleus.
When an atom undergoes alpha decay, its atomic number decreases by 2, and its mass number decreases by 4.

• The atom loses protons, changing its element.
• Example: Uranium-238 transforms into Thorium-234.

This process changes the identity of the element and results in a lighter nucleus. Alpha decay often occurs in heavy elements, helping them achieve stability.

Beta Decay

In beta decay, a neutron in the nucleus transforms into a proton. This transformation emits a beta particle, which is an electron.
As the atomic number increases by 1 due to the newly formed proton, the mass number remains the same.

• This happens because the overall number of nucleons (protons + neutrons) doesn't change.
• Example: Iodine-131 becomes Xenon-131 and Bismuth-214 turns into Polonium-214.

The increased atomic number means that the element changes, but this type of decay typically doesn't lead to a large change in atomic mass.

Positron Emission

Positron emission, or positive beta decay, involves a proton being converted into a neutron. During this process, a positron is emitted. A positron is similar to an electron but carries a positive charge.
This decreases the atomic number by 1, while the mass number stays constant.

• Example: Nitrogen-13 decays into Carbon-13.
• This type of decay allows unstable isotopes to become more stable by balancing the ratio of protons to neutrons.

Positron emission is important in processes like PET scans in medical imaging.

Atomic Number Change

The atomic number change is a common result of nuclear decay and directly influences the chemical identity of the element.
During nuclear decay processes such as alpha decay, beta decay, and positron emission, the atomic number changes because the number of protons in the nucleus changes.

• In alpha decay, the atomic number decreases by 2.
• In beta decay, the atomic number increases by 1.
• In positron emission, the atomic number decreases by 1.

These changes affect the element's position on the periodic table and its chemical properties. The ability to predict and understand these changes helps in fields like nuclear medicine and energy production.