Problem 19 - Chemistry The Central Science In Si Units

Question

(a) Give the names and chemical symbols for the three isotopes of hydrogen. (b) List the isotopes in order of decreasing natural abundance. (c) Which hydrogen isotope is radioactive? (d) Write the nuclear equation for the radioactive decay of this isotope.

Step-by-Step Solution

Answer

(a) Protium (\(^1H\), Deuterium (\(^2H\), Tritium (\(^3H\)). (b) Ordered by abundance: Protium, Deuterium, Tritium. (c) Tritium is radioactive. (d) \([^3_1H \rightarrow ^3_2He + e^- + \bar{\nu}_e]\).

Step 1: Identifying Isotopes of Hydrogen

Hydrogen has three isotopes. They are: Protium, which has the chemical symbol \(^1H\); Deuterium, represented as \(^2H\) or \(^2D\); and Tritium, denoted as \(^3H\).

Step 2: Ordering by Natural Abundance

In terms of natural abundance, the isotopes of hydrogen are ordered as follows: 1. Protium \(^1H\), 2. Deuterium \(^2H\), and 3. Tritium \(^3H\). Protium is overwhelmingly the most abundant, making up more than 99.98% of natural hydrogen.

Step 3: Identifying the Radioactive Isotope

Tritium \(^3H\) is the only radioactive isotope among the hydrogen isotopes. It undergoes radioactive decay.

Step 4: Writing the Nuclear Equation for Decay

The decay of tritium \(^3H\) involves beta decay. The nuclear equation for the decay is: \[ ^3_1H \rightarrow ^3_2He + e^- + \bar{u}_e \]In this equation, tritium decays to helium-3 \(^3He\) by emitting a beta particle (\(e^-\)) and an electron antineutrino (\(\bar{u}_e\)).

Key Concepts

Radioactive Decay

Radioactive decay is a natural process whereby an unstable atomic nucleus loses energy by emitting radiation. During this process, the atom changes from one type to another. For example, a carbon atom might change into a nitrogen atom over time.

An easy way to visualize this is as if atoms are ticking clocks counting down to change. The time it takes for half of the radioactive atoms present to decay is called the 'half-life'.

Key Points about Radioactive Decay:

• It occurs spontaneously. This means the atom changes without needing any help externally.
• Radiation can be particles (like electrons) or electromagnetic waves (like gamma rays).
• Every radioactive isotope has a characteristic half-life, which is different for each isotope.

Tritium

Tritium is one of the three isotopes of hydrogen, specifically named \(^3H\), containing one proton and two neutrons. It is unique among hydrogen isotopes because it is radioactive.

Characteristics of Tritium:

• It is radioactive and undergoes beta decay, where it transforms into helium-3.
• Tritium occurs naturally in trace amounts through interactions in the upper atmosphere but can also be artificially produced.
• In nature, it is extremely rare, contributing only a minuscule fraction to the abundance of hydrogen isotopes.

Usage of Tritium:

• Commonly used in self-powered lighting applications like watch dials and exit signs.
• Used in nuclear fusion processes as a possible future energy source.

Nuclear Equations

Nuclear equations are used to describe what happens during radioactive decay. They show the transformation of one element into another. Much like a recipe tells you how to bake a cake, a nuclear equation details the components before and after decay.

In the case of tritium, its decay is expressed as follows:\[ ^3_1H \rightarrow ^3_2He + e^- + \bar{u}_e \]This equation tells us that tritium (\(^3H\)) becomes helium-3 (\(^3He\)), and in the process releases a beta particle (an electron, \(e^-\)) and an electron antineutrino (\(\bar{u}_e\)).

Understanding Nuclear Equations:

• Superscripts denote the mass number, which is the total number of protons and neutrons.
• Subscripts denote atomic numbers, which count the number of protons.
• Particle emissions like beta particles are shown on the right of the arrow, representing products of decay.

Natural Abundance

Natural abundance refers to the relative percentage of an isotope compared to the total amount of the element found in nature.

For hydrogen, the concept showcases what portion each isotope accounts for:

• **Protium** \(^1H\): The most common hydrogen isotope, making up over 99.98% of hydrogen on earth. It contains just one proton.
• **Deuterium** \(^2H\): Comprising roughly 0.015% of natural hydrogen. Also called heavy hydrogen due to its extra neutron.
• **Tritium** \(^3H\): Almost absent in nature, this isotope is rare and difficult to find except when generated through cosmic rays or in laboratories.

Relevance of Natural Abundance:

• It helps scientists understand the composition of the earth and celestial bodies.
• Aids in analyzing environmental and climatic changes.