Difference Between Isotopes and Elements

The key difference between isotopes and elements is that the isotopes are different forms of the same chemical element whereas the elements are species of atoms having the same number of protons in the atomic nuclei.

A similar type of atoms can undergo slight changes to form different isotopes. An element may have several isotopes. The nature of each isotope contributes to the nature of an element. Here, we will be discussing in detail about the isotopes and elements in order to elucidate the difference between isotopes and elements.

CONTENTS

1. Overview and Key Difference
2. What are Isotopes
3. What are Elements
4. Side by Side Comparison – Isotopes vs Elements in Tabular Form
5. Summary

What are Isotopes?

Atoms of the same element can be different from each other. These different atoms of the same element are isotopes. They are different from each other by having a different number of neutrons. Since the neutron number is different, their mass number also differs. However, the isotopes of the same element have the same number of protons. In nature, different isotopes occur in varying quantities. Therefore, we can give their occurrence as a percentage value called relative abundance. For instance, hydrogen has three isotopes such as protium, deuterium and tritium. The number of protons in their atomic nuclei is the same, but the number of neutrons is different. Their neutrons and relative abundances are as follows.

• ¹H – no neutrons, relative abundance is 99.985%
• ²H- one neutron, relative abundance is 0.015%
• ³H- two neutrons, relative abundance is 0%

The number of neutrons a nucleus can hold differs from element to element. Among these isotopes, only some are stable. For instance, oxygen has three stable isotopes, and tin has ten stable isotopes. Most of the times, simple elements have the same neutron number as the proton number. But in heavy elements, more neutrons are there than the number of protons.

Further, the number of neutrons is important to balance the stability of the nuclei. When the nuclei are too heavy, they become unstable and therefore, those isotopes become radioactive. For example, ²³⁸U emits radiation and decays into much smaller nuclei. Isotopes may have different properties because of their different masses. For example, they can have different spins. Thus, their NMR spectra differ. However, their electron number is similar giving rise to similar chemical behaviour.

What are Elements?

We are familiar with the word “element,” because we learn about them in the periodic table. There are about 118 chemical elements in the periodic table, and they are arranged according to their atomic number. An element is a chemical species, which represent only a single type of atoms. Hence, they are pure. Further, the atoms of the same element have the same number of protons in their atomic nuclei. But, the number of neutrons can differ from each other. For example, the smallest element is hydrogen. Silver, gold, platinum are some of the commonly known precious elements.

Each element has an atomic mass, atomic number, symbol, electronic configuration, etc. Although most of the elements are naturally occurring, there are some synthetic elements like Californium, Americium, Einsteinium, and Mendelevium. We can categorize all the elements into three groups; as metals, metalloids, and nonmetals.

Further, we can categorize them into groups and periods based on more specific characteristics. Also, elements in the same group or period share certain common characteristics, and some properties may change sequentially when you go through a group or period. Moreover, elements can undergo chemical changes to form various compounds; however, we cannot break down elements further by simple chemical methods.

What is the Difference Between Isotopes and Elements?

The term chemical element describes a species of atoms while the term isotopes describe different forms of the same chemical element. Therefore, the key difference between isotopes and elements is that isotopes are different forms of the same chemical element whereas elements are species of atoms having the same number of protons in the atomic nuclei. Furthermore, one other difference between isotopes and elements is that the isotopes have different numbers of neutrons, but chemical elements can have either the same number of neutrons or a different number of neutrons; but they never have the same number of protons.

As another important difference between isotopes and elements, we can say that atomic mass of an isotope can be calculated by simply adding the total mass of protons and the neutrons in the atomic nuclei whereas we can calculate the atomic mass of a chemical element using the atomic masses of its isotopes and their relative abundance.

Summary – Isotopes vs Elements

Isotopes are different atomic forms of the same chemical element. The key difference between isotopes and elements is that the isotopes are different forms of the same chemical element whereas the elements are species of atoms having the same number of protons in the atomic nuclei.

Reference:

1. “Chemical Element.” Wikipedia, Wikimedia Foundation, 11 Nov. 2018. Available here  
2. Helmenstine, Anne Marie, Ph.D. “Isotopes Definition and Examples in Chemistry.” ThoughtCo, Oct. 22, 2018. Available here  

Image Courtesy:

1.”204 Isotopes of Hydrogen-01″By OpenStax College – Anatomy & Physiology, Connexions Web site.  (CC BY 3.0) via Commons Wikimedia
2.”Simple Periodic Table Chart-en”By Offnfopt – Own work, (Public Domain) via Commons Wikimedia