Problem 10 - AP Biology Premium Prep 2021

Question

A radioactive isotope of hydrogen, \({ }^{3} \mathrm{H},\) is called tritium. Tritium differs from the more common form of hydrogen because (A) it contains two neutrons and one proton in its nucleus \((\mathrm{B})\) it contains one neutron and two protons in its nucleus (C) it differs by its atomic number (D) it is radioactive and therefore gives off one electron

Step-by-Step Solution

Answer

Tritium differs from the more common form of hydrogen because \(it \ contains \ two \ neutrons \ and \ one \ proton \ in \ its \ nucleus.\) The correct answer is (A).

Step 1: Understand hydrogen isotopes

An element is defined by its atomic number, which represents the number of protons in the nucleus. Hydrogen has an atomic number of 1, meaning it has one proton. However, hydrogen has different isotopes, which have the same number of protons but different numbers of neutrons. The most common isotope of hydrogen has no neutrons (protium), but tritium has two neutrons.

Step 2: Evaluate the given options

Now, we will evaluate each option to identify the correct answer. (A) it contains two neutrons and one proton in its nucleus: This option is correct. Tritium is an isotope of hydrogen with two neutrons and one proton in its nucleus, making it different from the more common form of hydrogen, which has no neutrons. (B) it contains one neutron and two protons in its nucleus: This option is incorrect. If it had two protons, it wouldn't be hydrogen–it would be helium. (C) it differs by its atomic number: This option is incorrect. Both tritium and common hydrogen have the same atomic number (1), which represents the number of protons in the nucleus. (D) it is radioactive and therefore gives off one electron: This option is partially correct. Tritium is radioactive, but radioactivity is not the primary difference between tritium and the more common form of hydrogen. Radioactivity is a byproduct of tritium's different nucleus structure, which contains two neutrons and one proton.

Step 3: Choose the correct answer

Based on the evaluation of the given options, option (A) is the correct answer. Tritium differs from the more common form of hydrogen because it contains two neutrons and one proton in its nucleus.

Key Concepts

Tritium

Tritium is a special kind of hydrogen isotope, distinguished by its unique atomic structure. It is referred to as hydrogen-3, denoted by \({ }^3\text{H}\). Unlike hydrogen's most common isotope protium, which contains merely one proton and no neutrons, tritium harbors two neutrons alongside one proton in its nucleus. This gives tritium a total atomic mass of 3 amu (atomic mass units).

Tritium is noteworthy because of its radioactivity, which sets it apart from other hydrogen isotopes. Although all isotopes of hydrogen share the same single proton, it's the neutron count that makes tritium distinctively unstable and radioactive. This radioactivity arises because the extra neutrons in tritium cause the nucleus to be less stable, leading it to emit radiation to reach a more stable state.

Hydrogen Isotopes

Hydrogen, the simplest and most abundant element in the universe, can exist in three isotopic forms: protium, deuterium, and tritium. These variations are known as hydrogen isotopes.

All hydrogen isotopes contain only one proton in their nucleus, which explains why they share the same atomic number, 1. However, they differ in the number of neutrons:

• Protium: Has no neutrons and is the most common hydrogen isotope found in nature.
• Deuterium: Contains one neutron along with the single proton.
• Tritium: Encompasses two neutrons and a single proton.

The differences among these isotopes impact their weight, physical properties, and stability. Tritium, being heavier due to its two neutrons, is less stable and exhibits radioactive properties, which is notably significant in nuclear science and various applications including glow-in-the-dark devices and as a tracer in biochemical research.

Atomic Structure

The atomic structure of an element is defined by the arrangement of protons, neutrons, and electrons within its atom. For hydrogen, this simplicity is both profound and illustrative of atomic basics.

Hydrogen atoms are defined by having one proton. The number of neutrons present distinguishes its isotopes:

• Protium: One proton and zero neutrons, with one electron orbiting the nucleus.
• Deuterium: One proton, one neutron, and one electron.
• Tritium: One proton, two neutrons, and one electron.

Understanding atomic structure helps us grasp the concept of isotopes. Isotopes are variants of the same element that have the same number of protons but differ in the number of neutrons. This difference can dramatically affect some properties, such as radioactivity, as seen in tritium. The atomic structure of an element is therefore pivotal in determining its chemical behavior and physical properties.

Radioactivity

Radioactivity refers to the process by which unstable atomic nuclei lose energy by emitting radiation. This phenomenon is crucial to understanding isotopes like tritium.

Tritium is radioactive because its nucleus is unstable. Radioactivity can be natural or artificially induced, but in isotopes like tritium, it occurs naturally as the atom seeks a more stable state. During this process, tritium transforms into helium-3 by emitting a beta particle (an electron or positron), which is a common type of radioactive decay.

The radioactivity of tritium is often exploited in different technologies:

• Emitting low-energy radiation, tritium is used in self-luminous applications like exit signs and wristwatch dials.
• In scientific research, tritium acts as a tracer for tracking movement and exchanges in metabolic studies.

Understanding radioactivity is crucial for ensuring the safe handling of radioactive substances and harnessing their potential in scientific and practical applications.