Define the Term Isotope?
Isotope definition or isotope meaning can be given as the chemical element variants that possess the same count of electrons and protons but with a different neutron count. In other terms, isotopes are the variants of elements that vary in their nucleon numbers because of the difference in their respective nuclei's total neutron number. For example, carbon-12, carbon-13, and carbon-14 are all the isotopes of carbon. Carbon-12 comprises a total of 6 neutrons, carbon-13 contains a total of 7 neutrons, and Carbon-14 comprises a total of 8 neutrons.
Representation of Isotopes
Isotopes can be majorly represented in 2 different ways, which are given as follows:
By writing the name of the element followed by a hyphen and the mass number of the isotope. For example, uranium-235 and uranium-239 are two different isotopes of the element uranium.
Following the AZE notation (which is also known as the standard notation). This involves writing the symbol of an element and prefixing the atomic number in subscript and the mass number in superscript. For example, the uranium-239 isotope can be represented as 23992U, whereas, uranium-235 isotope can be represented as 23592U.
Determining the Neutron Number in an Isotope
The total neutron number present in an isotope nucleus is determined by subtracting the element's atomic number from the mass number of the isotope. As an example, the atomic number of carbon is 6, and the 12C isotope of carbon contains a mass number of 12. Thus, the total neutron number present in the carbon-12 isotope is equal to 6.
Stable Isotopes, Radioactive Isotopes, and Primordial Isotopes
A few isotopes contain unstable atomic nuclei that experience radioactive decay. These specific isotopes are radioactive in nature and are, thus, called radioisotopes (otherwise radionuclides). A few examples of the radioactive isotopes can be given as chlorine-36, uranium-235, uranium-238, and carbon-14, tritium (hydrogen-3).
Primordial nuclides are the ones that existed because of the solar system formation. Out of 339 naturally occurring isotopes on Earth, a total of 286 are known to be the primordial isotopes.
A few isotopes are known to have extremely long half-lives (in the order, hundreds of millions of years). Such types of isotopes are commonly known as either stable isotopes or stable nuclides. Some common examples of stable nuclides are given as oxygen-16, oxygen-17, oxygen-18, carbon-12, and carbon-13.
Comparison Between the Isobars and Isotopes
An isotope is described as a variation of an element that possesses a similar atomic number but with a different mass number. A group of isotopes with any element will always contain a similar number of electrons and protons. Moreover, they will vary in the number of neutrons held by their respective nuclei. One example of a group of isotopes is given as hydrogen-1 (so-called, protium), hydrogen-2 (so-called, deuterium), and hydrogen-3 (so-called, tritium).
On the other side, isobars are described as the chemical species that contain a similar number of nucleons, with different atomic numbers. The isobar groups will differ in the number of protons, in the atomic number, the number of neutrons, and the number of electrons. However, they will always contain a similar number of nucleons. Thus, the sum of the number of neutrons and the number of protons will always be the same in an isobar group. An example of an isobar group is given by argon-40, chlorine-40, sulfur-40, potassium-40, and calcium-40.
To simplify more, isotopes hold similar atomic numbers but different mass numbers. On the other side, the isobars contain similar mass numbers but with different atomic numbers.
Applications of Isotopes
One of the important applications of isotopes is given in the determination of the isotopic signature of the element samples through isotope analysis. In general, this is done via the process of isotope ratio mass spectrometry.
The chemical reaction mechanism can be determined using isotopic substitution. The change in the rate of reaction can be measured on the basis of the kinetic isotope effect.
Isotopes are also used to determine the concentration of several substances/elements via isotope dilution.
An Isotope of an Element
The isotope of an element can be described as one of the many variants of the specific chemical element that carries a similar number of electrons and protons as the atomic number of the element but contains a variable number of neutrons when compared to the other variants (isotopes) of the element. Alternately, isotopes can be defined as variants of elements that differ in their nucleon numbers because of the difference in the total number of neutrons in their respective nuclei.
Isotopes of Hydrogen
The three isotopes of hydrogen can be listed as follows.
Hydrogen-1 or Protium
This isotope of hydrogen holds 1 electron, 1 proton, and zero neutrons.
Hydrogen-2 or Deuterium
This isotope of hydrogen holds 1 electron, 1 proton, and 1 neutron.
Hydrogen-3 or Tritium
This isotope of hydrogen holds 1 electron, 1 proton, and 2 neutrons. It should also be noted that this isotope of hydrogen is radioactive.
FAQs on Isotope Meaning
1. What is the fundamental definition of an isotope in Chemistry?
In chemistry, isotopes are defined as variants of a particular chemical element which have the same number of protons but a different number of neutrons in their atomic nuclei. Since the atomic number (Z) is determined by the number of protons, all isotopes of an element share the same atomic number and position on the periodic table. However, they differ in their mass number (A), which is the total count of protons and neutrons.
2. What are some common examples of isotopes?
Some of the most common and widely taught examples of isotopes include:
- Hydrogen: It has three main isotopes: Protium (¹H) with 1 proton and 0 neutrons, Deuterium (²H) with 1 proton and 1 neutron, and Tritium (³H) with 1 proton and 2 neutrons.
- Carbon: Carbon-12 (¹²C) is the most abundant, with 6 protons and 6 neutrons. Carbon-13 (¹³C) has 6 protons and 7 neutrons, and Carbon-14 (¹⁴C) has 6 protons and 8 neutrons. Carbon-14 is radioactive.
3. How are isotopes represented using standard chemical notation?
Isotopes are commonly represented using the AZE notation. In this format, the mass number (A) is written as a superscript and the atomic number (Z) is written as a subscript, both preceding the element's symbol (E). For example, the isotope Uranium-235 is written as ²³⁵₉₂U, where 235 is the mass number and 92 is the atomic number.
4. How are isotopes different from isobars?
Isotopes and isobars are often confused but describe opposite relationships. The key difference lies in what is the same and what is different:
- Isotopes: Atoms of the same element (same atomic number) but with a different mass number. Example: Carbon-12 (¹²C) and Carbon-14 (¹⁴C).
- Isobars: Atoms of different elements (different atomic numbers) but with the same mass number. Example: Argon-40 (⁴⁰₁₈Ar) and Calcium-40 (⁴⁰₂₀Ca).
5. What are the main types of isotopes found in nature?
Isotopes are broadly classified into two main types based on their nuclear stability:
- Stable Isotopes: These have a stable atomic nucleus that does not undergo spontaneous radioactive decay. They persist indefinitely. Examples include Carbon-12 and Oxygen-16.
- Radioactive Isotopes (Radioisotopes): These have an unstable atomic nucleus that decays over time, emitting radiation in the process. Each radioisotope has a characteristic half-life. Examples include Carbon-14, Uranium-235, and Cobalt-60.
6. Why are these variants of an element called 'isotopes'?
The name 'isotope' comes from the Greek words 'isos' (meaning 'same') and 'topos' (meaning 'place'). This name was proposed by Margaret Todd in 1913. It reflects the fact that all isotopes of a single element occupy the same place on the periodic table because they all have the same atomic number (number of protons).
7. What are some important real-world applications of isotopes?
Isotopes have numerous critical applications across science and industry. For example:
- Medical Diagnosis and Treatment: Cobalt-60 is used in radiotherapy to destroy cancer cells, and Iodine-131 is used to diagnose and treat thyroid disorders.
- Carbon Dating: The radioisotope Carbon-14 is used to determine the age of ancient organic materials and archaeological artifacts.
- Nuclear Power: Uranium-235 is a key fuel source in nuclear reactors for generating electricity through nuclear fission.
8. Do different isotopes of an element have the same chemical properties? Why or why not?
Yes, different isotopes of an element generally have nearly identical chemical properties. This is because an atom's chemical behaviour is primarily determined by its electron configuration, specifically the valence electrons. Since all isotopes of an element have the same number of protons, they also have the same number of electrons to remain electrically neutral. Therefore, their electron structures are the same, leading to the same chemical reactivity. However, they may have slightly different physical properties (like density and diffusion rate) due to their difference in mass.
