Nucleons and Isotopes

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Nucleons and Isotopes

This lesson aligns with NGSS PS1.A

Introduction

Every atomic nucleus, excluding the simplest form of hydrogen, is composed of both protons and neutrons. The unique identity of each nucleus is defined by the specific count of protons and neutrons it contains. Protons are subatomic particles with a positive charge, while neutrons are subatomic particles characterized by a neutral charge. Nucleons collectively refer to the particles present within the nucleus of atoms. Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons in their nuclei. In this article, we will learn about nucleons, their properties, nuclides and isotopes.

Nucleons

Nucleons are subatomic particles that are found in the nucleus of an atom. There are two main types of nucleons: protons and neutrons. The atom can be likened to a miniature solar system, where electrons orbit a central star, analogous to the nucleus composed of nucleons.

Both protons and neutrons contribute to the mass of an atom, and they are bound together by the strong nuclear force within the atomic nucleus.

For instance, in a nucleus of gold, there are 79 protons and 118 neutrons, giving a total of 197 nucleons altogether.

Protons:

Positively charged particles, protons are one of the fundamental building blocks of an atomic nucleus. The number of protons in an atom determines its atomic number, which, in turn, identifies the element.

For example, hydrogen, the simplest element, boasts a single proton, while the element carbon is characterized by six protons.

Neutrons:

Neutrons are neutral particles, meaning they have no electric charge. Neutrons, along with protons, contribute to the mass of the atomic nucleus. They play an important role in stabilizing the nucleus by offsetting the electrostatic repulsion between positively charged protons.

The total number of nucleons in a nucleus is known as nucleon number (or mass number) A.
The nucleon number is equal to the sum of the number of neutrons N in the nucleus, and the number of protons Z. A = N+Z

Binding Energy Per Nucleon

Atomic nuclei are composed of protons and neutrons, yet the total mass of a nucleus is slightly less than the combined mass of its individual protons and neutrons. The difference is the measure of binding energy per nucleon, the force that binds nucleons within the nucleus. The binding energy per nucleon represents the energy required to disassemble a nucleus into its constituent parts and reflects the stability of the nucleus. A higher binding energy per nucleon indicates a more stable nucleus.

The binding energy per nucleon can be determined from the following relationship:

Nuclear binding energy = Binding Energy/Nucleon number

For instance, the binding energy per nucleon for a helium atom is 28.3/4 = 7.1 MeV.

Nuclide:

The representation of an atom's nucleus involves using the element symbol along with the nucleon number and proton number. This is demonstrated in the examples below:

Oxygen-16 [math]{::}_8^16O[/math]

Gold-197 [math]{::}_79^197Au [/math]

Uranium-238[math]{::}_92^238U[/math]

A unique arrangement of protons and neutrons within a nucleus is referred to as a nuclide.

What are Isotopes?

Isotopes of a particular element share the same atomic number but have different atomic masses due to variations in the number of neutrons. This results in isotopes having similar chemical properties but differing in their physical properties, such as atomic mass and stability. For instance, three different naturally occurring forms of neon are: [math]{::}_10^20Ne[/math] [math]{::}_10^21Ne [/math] [math]{::}_10^22Ne[/math].

The first has 10 neutrons in the nucleus, the second 11 neutrons and the third 12 neutrons. These three types of neon nuclei are known as isotopes of neon.

Stable Isotopes:

Stable isotopes maintain their nuclear structure over time without undergoing radioactive decay. Carbon, a fundamental element for life, exists in stable isotopic forms such as carbon-12 and carbon-13, carbon-14.

Unstable Isotopes:

In contrast, unstable isotopes, also known as radioactive isotopes. This process, known as radioactive decay, involves the emission of particles such as alpha or beta particles, leading to the conversion of the isotope into another element. For instance, Uranium-238, a common radioactive isotope, decays into lead-206.

The different numbers of neutrons in isotopes of an element result in distinct relative atomic masses for each isotope. These differences extend to various physical properties, including density and boiling point. For instance, heavy water, containing deuterium, exhibits a boiling point of 104 °C under standard atmospheric pressure.

Summary

Protons are subatomic particles with a positive charge, while neutrons are subatomic particles characterized by a neutral charge.
Nucleons are subatomic particles of either number of protons or number of neutrons that are found in the nucleus of an atom.
The binding energy per nucleon represents the energy required to disassemble a nucleus into its constituent parts and reflects the stability of the nucleus.
A higher binding energy per nucleon indicates a more stable nucleus.
Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons in their nuclei.

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