Problem 37 - General Chemistry: Principles and Modern Applications

Question

Iodine has many radioactive isotopes. Iodine-123 is a radioactive isotope used for obtaining images of the thyroid gland. Iodine-123 is administered to patients in the form of sodium iodide capsules that contain \(123 \mathrm{I}^{-}\) ions. Determine the number of neutrons, protons, and electrons in a single \(^{123} \mathrm{I}^{-}\) ion.

Step-by-Step Solution

Answer

In a single \(^{123} \mathrm{I}^{-}\) ion, there are 53 protons, 70 neutrons, and 54 electrons.

Step 1: Determine the number of protons

The number of protons in an isotope is equivalent to the atomic number of that element. The atomic number of iodine (\( \mathrm{I} \)) is 53. So, there are 53 protons in \(^{123} \mathrm{I}^{-}\).

Step 2: Determine the number of neutrons

The mass number of an isotope is the sum of the number of protons and neutrons in the nucleus. So, to find the number of neutrons in \(^{123} \mathrm{I}^{-}\), subtract the number of protons from the mass number. Hence, the number of neutrons is 123 - 53 = 70.

Step 3: Determine the number of electrons

In a neutral atom, the number of electrons is the same as the number of protons. However, in an ion like \(^{123} \mathrm{I}^{-}\), the negative charge indicates that there is one extra electron. So, the number of electrons is 53 (protons) + 1 (extra from the negative charge) = 54.

Key Concepts

Iodine-123

Iodine-123 is a noteworthy radioactive isotope. It plays a significant role in nuclear medicine, primarily due to its optimal half-life of approximately 13.2 hours and its gamma radiation emissions. These properties make it especially useful for creating images in diagnostic procedures without unnecessarily prolonging radiation exposure for the patient. This isotope behaves similarly to non-radioactive iodine and is predominantly utilized in the form of sodium iodide (NaI) capsules. When administered, it participates in the thyroid gland's natural iodine uptake processes, allowing for effective imaging of thyroid function and structure. Furthermore, Iodine-123 decays into a stable form of Xenon, ensuring that it does not leave any long-lasting radioactive residue in the body.

• Optimal half-life: 13.2 hours
• Gamma radiation emission
• Used in sodium iodide form

Thyroid Imaging

Thyroid imaging is crucial in diagnosing and managing thyroid-related disorders. The thyroid gland is responsible for producing hormones that regulate metabolism, and its dysfunction can lead to a variety of health issues. Utilizing Iodine-123 in thyroid scans provides clear images of the gland. Once administered, Iodine-123 is selectively absorbed by the thyroid, where it mimics the behavior of natural iodine. Gamma cameras are then employed to detect the gamma rays emitted by the isotope, capturing detailed images that reveal the size, shape, and activity of the thyroid. These scans are essential for identifying conditions like hyperthyroidism, Graves' disease, or thyroid nodules.

• Diagnostic tool for thyroid disorders
• Targeted absorption by thyroid gland
• Gamma camera imaging process

Atomic Structure

Understanding atomic structure is vital in grasping how isotopes like Iodine-123 function. An atom consists of three main components: protons, neutrons, and electrons. The number of protons defines the element and is known as the atomic number. For iodine, this number is 53, indicating 53 protons. The mass number of an isotope is the sum of protons and neutrons; for Iodine-123, the mass number is 123, leading to 70 neutrons (123 - 53 = 70). Electrons are equal to protons in neutral atoms, but in ions, this can change. The ion Iodine-123 in its negative form ("")] has an additional electron, totaling 54 electrons (53 protons + 1 extra electron).

• Atomic number: 53 for iodine
• Mass number: sum of protons and neutrons
• Extra electron in negatively charged ions