Problem 48 - Chemistry

Question

a. List the noble gas elements. Which of the noble gases has only radioactive isotopes? (This situation is indicated on most periodic tables by parentheses around the mass of the element. See inside front cover.) b. Which lanthanide element and which transition element have only radioactive isotopes?

Step-by-Step Solution

Answer

The noble gas elements are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn). Among them, Radon (Rn) has only radioactive isotopes. The lanthanide element with only radioactive isotopes is Promethium (Pm) with atomic number 61, and the transition element with only radioactive isotopes is Technetium (Tc) with atomic number 43.

Step 1: Part a: Listing the noble gas elements

The noble gases are the elements found in Group 18 (VIII) of the periodic table. These elements include: 1. Helium (He) 2. Neon (Ne) 3. Argon (Ar) 4. Krypton (Kr) 5. Xenon (Xe) 6. Radon (Rn)

Step 2: Identifying the noble gas with only radioactive isotopes

Among the noble gases, Radon (Rn) is the only one with radioactive isotopes. It is usually indicated on the periodic table by parentheses around its mass number.

Step 3: Part b: Identifying the lanthanide element and the transition element with only radioactive isotopes

We will again refer to the periodic table to find the required elements. 1. The lanthanide element with only radioactive isotopes is Promethium (Pm). Its atomic number is 61. 2. The transition element with only radioactive isotopes is Technetium (Tc). Its atomic number is 43.

Key Concepts

Radioactive Isotopes

Radioactive isotopes are atoms with an unstable nucleus that tend to lose particles and energy to reach a more stable state. These isotopes undergo radioactive decay, a process that occurs over time, during which they transform into a different element or a different isotope of the same element. This decay can produce:

• Alpha particles, which are positively charged and fairly heavy.
• Beta particles, which can be negatively charged (electrons) or positively charged (positrons).
• Gamma rays, which are energetic photons without a charge.

Understanding the decay process is essential, as it is the basis for radiometric dating and nuclear medicine. Radon (Rn), a noble gas with only radioactive isotopes, is a classic example in nature. Being colorless and odorless, Radon is often undetected in houses, accumulating from soil or rock sources. It's important because of its health implications—prolonged exposure can lead to lung cancer.

Lanthanide Elements

Lanthanide elements, also known as rare earth elements, are found in the f-block of the periodic table. They include elements with atomic numbers 57 through 71. Lanthanides have unique properties, such as

• Silvery-white appearance
• High reactivity, particularly with oxygen
• Magnetic and phosphorescent properties

Promethium (Pm), atomic number 61, is unique among the lanthanides because it only exists as radioactive isotopes. Unlike other lanthanides, Promethium is scarce and found only in trace amounts in uranium ores. However, it can be synthesized in nuclear reactors and has applications in luminous paints and certain types of batteries. These specialized uses capitalize on its radioactive nature, making it valuable despite its rarity.

Transition Elements

Transition elements are metals placed in the d-block of the periodic table, spanning groups 3 through 12. These elements are known for their ability to form variable oxidation states, which leads to the formation of colorful compounds. Key characteristics of transition elements include:

• Good conductors of electricity
• High melting and boiling points
• Ability to form alloys with other metals

Technetium (Tc), with an atomic number of 43, is unique among transition metals as it has no stable isotopes—all its isotopes are radioactive. Discovered as a byproduct of nuclear fission, Technetium plays a crucial role in medicine, especially in imaging techniques due to its radioactive properties. It is commonly used in diagnostic tests like heart scans, making it a vital element in modern healthcare.