Problem 38 - General Chemistry: Principles and Modern Applications

Question

Iodine-131 is a radioactive isotope that has important medical uses. Small doses of iodine-131 are used for treating hyperthyroidism (overactive thyroid) and larger doses are used for treating thyroid cancer. Iodine-131 is administered to patients in the form of sodium iodide capsules that contain \(^{131} \mathrm{I}^{-}\) ions. Determine the number of neutrons, protons, and electrons in a single \(^{131} \mathrm{I}^{-}\) ion.

Step-by-Step Solution

Answer

In a single iodine-131 ion, there are 53 protons, 78 neutrons, and 54 electrons.

Step 1: Determining the number of Protons

The atom in question is Iodine (\(\mathrm{I}\)). The atomic number of iodine, which is given by its place in the periodic table, is 53. This represents the number of protons. Thus, the number of protons in iodine-131 is 53.

Step 2: Determining the number of Neutrons

To find the number of neutrons in a nucleus, the atomic number (No. of protons) is subtracted from the mass number. In this case, Iodine-131, the atomic mass is 131 (given in the notation). So, the number of neutrons = atomic mass – atomic number = \(131 - 53 = 78\). Therefore, there are 78 neutrons in a single iodine-131 isotope.

Step 3: Determining the number of Electrons

In an uncharged, neutral atom, the number of electrons is equal to the number of protons. However, the iodine in the form given in the problem (\(^{131} \mathrm{I}^{-}\)) is an ion with a negative charge. This means it has gained one extra electron. Therefore, the number of electrons = atomic number + 1 (due to the negative charge) = \(53 + 1 = 54\). Thus, there are 54 electrons in a single iodine-131 ion.

Key Concepts

Iodine-131

Iodine-131 is an isotope of iodine that is both radioactive and important in medical applications. Its radioactivity means it spontaneously emits radiation as it decays to a more stable form. This is crucial for its use in therapies, especially as it emits beta particles, which are effective at targeting and destroying specific cells, such as those in thyroid tissues.
Iodine-131 has a half-life of about eight days, making it suitable for medical treatments since it remains active long enough to be effective but not excessively long to pose prolonged radiation risks to patients. In medical use, iodine-131 is often provided in the form of sodium iodide and is specially designed to target thyroid cells, leveraging the thyroid gland's natural uptake of iodine. The efficiency and precision of iodine-131 treatments stem directly from its isotope properties, which make it a valuable tool in treating thyroid conditions.

Atomic Structure

The atomic structure is foundational to understanding elements and their isotopes. Essentially, an atom is composed of a nucleus surrounded by electrons. The nucleus contains protons and neutrons, which are collectively called nucleons.

• Protons are positively charged particles.
• Neutrons are neutral particles that add to the atomic mass.
• Electrons are negatively charged particles that orbit the nucleus.

The number of protons in an atom's nucleus determines the element's identity on the periodic table. This is known as its atomic number. For example, iodine has 53 protons. Neutrons, though not affecting the charge, play a role in defining different isotopes of the same element, like iodine-131 versus iodine-127. Electrons are crucial for dictating the atom's chemical properties, especially in interactions and bonding.

Isotopes in Medicine

Isotopes play a significant role in medicine, providing diagnostic and therapeutic solutions. Medical isotopes are often chosen for their radioactive properties, which, when carefully managed, allow for effective treatments. A prime example is iodine-131, used in therapies due to its ability to emit radiation that can precisely target diseased cells, as seen in thyroid treatments.
In diagnostics, isotopes can be used to trace substances within the body due to their radioactive decay, which can be captured on film or by detectors. This technique is valuable in nuclear medicine, allowing for detailed imaging without invasive procedures. Such applications require isotopes with specific half-lives to ensure they remain active only for the duration of the medical need. Safety protocols are crucial, ensuring that the benefits far outweigh any risks from radiation exposure.

Ionic Compounds

Ionic compounds are formed through the electrostatic interaction between positively and negatively charged ions. These are typically created when metals transfer electrons to non-metals, resulting in positive metal ions (cations) and negative non-metal ions (anions).
In the context of iodine-131, when it forms an ionic compound like sodium iodide ( NaI ), it involves the iodide ( I^- ) anion. This formation stems from iodine accepting an extra electron to complete its valence shell, resulting in a negative charge. Meanwhile, sodium provides this electron, becoming a positively charged ion. Ionic compounds are characterized by their high melting and boiling points due to the strong ionic bonds. They typically dissolve in water, conducting electricity in solution. In medical applications, compounds like sodium iodide can be easily administered as they readily dissolve in bodily fluids, facilitating delivery to target areas such as the thyroid gland.