Which Of The Following Represents A Pair Of Isotopes

Which of the Following Represents a Pair of Isotopes? Understanding Isotopes and Their Significance

Understanding isotopes is crucial in various scientific fields, from chemistry and physics to medicine and environmental science. This article delves deep into the concept of isotopes, explaining what they are, how they differ from other similar atomic species, and how to identify them. We'll explore several examples and clarify common misconceptions surrounding isotopes. By the end, you'll be able to confidently identify pairs of isotopes from a given set of options.

What are Isotopes?

Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. This means they possess the same atomic number (which defines the element) but different mass numbers (the total number of protons and neutrons). The difference in neutron number leads to variations in atomic mass, but the chemical properties remain largely the same due to the identical number of protons and electrons.

Let's break this down further:

• Atomic Number: This number represents the number of protons in an atom's nucleus. It uniquely identifies an element. For example, all atoms with an atomic number of 6 are carbon atoms.
• Mass Number: This is the total number of protons and neutrons in an atom's nucleus. It determines the atom's mass.
• Neutrons: These subatomic particles reside in the nucleus alongside protons. They contribute to the atom's mass but not its charge (as they are neutral).

Identifying Isotopes: A Step-by-Step Guide

To identify a pair of isotopes, you need to carefully examine the atomic number and the mass number of the atoms in question. Here's a step-by-step approach:

1. Identify the Atomic Number: Locate the atomic number for each atom. This is usually represented by the subscript before the element's symbol (e.g., ⁶C for carbon).
2. Compare Atomic Numbers: If the atomic numbers are the same, the atoms belong to the same element. This is a necessary but not sufficient condition for them to be isotopes.
3. Identify the Mass Number: Locate the mass number for each atom. This is usually represented by the superscript before the element's symbol (e.g., ¹²C for carbon-12).
4. Compare Mass Numbers: If the mass numbers are different, while the atomic numbers are the same, you have identified a pair of isotopes.

Examples of Isotope Pairs

Let's illustrate this with some examples:

Example 1:

• ¹²C and ¹⁴C (Carbon-12 and Carbon-14)

Both have an atomic number of 6 (indicating they are both carbon atoms). However, their mass numbers differ (12 and 14, respectively). Therefore, ¹²C and ¹⁴C are isotopes of carbon. The difference lies in the number of neutrons: ¹²C has 6 neutrons, while ¹⁴C has 8 neutrons.

Example 2:

• ¹H and ²H (Protium and Deuterium)

These are isotopes of hydrogen. Both have an atomic number of 1, but their mass numbers are 1 and 2, respectively. This difference stems from the number of neutrons: ¹H has 0 neutrons, while ²H (deuterium) has 1 neutron. Deuterium is also known as heavy hydrogen.

Example 3:

• ¹⁶O and ¹⁸O (Oxygen-16 and Oxygen-18)

Oxygen-16 and Oxygen-18 are isotopes of oxygen. They share an atomic number of 8, but their mass numbers are 16 and 18, respectively, due to a difference in the number of neutrons.

Isotopes vs. Ions vs. Isomers: Clarifying the Differences

It's important to distinguish isotopes from other similar atomic species:

• Isotopes: Same atomic number (number of protons), different mass number (number of neutrons).
• Ions: Atoms with a different number of electrons than protons, resulting in a net electric charge. Ions of the same element will have the same number of protons but different numbers of electrons.
• Isomers: Molecules with the same molecular formula but different arrangements of atoms. This is a difference in structure rather than the number of subatomic particles in the nucleus.

The Significance of Isotopes

Isotopes play a significant role in various fields:

• Radioactive Dating: Radioactive isotopes, such as Carbon-14, are used to determine the age of artifacts and fossils. The decay rate of these isotopes allows scientists to estimate the time elapsed since the organism died.
• Medical Imaging and Treatment: Radioactive isotopes are employed in medical imaging techniques like PET (positron emission tomography) scans and are used in radiation therapy to treat cancer.
• Nuclear Energy: Certain isotopes, like Uranium-235, are used as fuel in nuclear power plants.
• Industrial Applications: Isotopes are used in various industrial processes, including tracing materials, measuring flow rates, and gauging thickness.
• Scientific Research: Isotopes are essential tools in various scientific research areas, including understanding chemical reactions, studying metabolic processes, and analyzing environmental samples.

Identifying Isotopes in Multiple Choice Questions

Let’s consider some multiple choice examples to further solidify your understanding.

Question 1: Which of the following represents a pair of isotopes?

(a) ¹²C and ¹⁴N (b) ¹⁶O and ¹⁸O (c) ¹H and ²He (d) ³He and ⁴He

Answer: (b) ¹⁶O and ¹⁸O. Both have the same atomic number (8 for oxygen), but different mass numbers (16 and 18).

Question 2: Which pair represents isotopes of the same element?

(a) ³H and ³He (b) ¹⁴N and ¹⁵N (c) ²³⁵U and ²³⁸Pu (d) ²H and ³Li

Answer: (b) ¹⁴N and ¹⁵N. Both have the same atomic number (7 for nitrogen).

Question 3: Which of the following is NOT a pair of isotopes?

(a) ²³⁸U and ²³⁵U (b) ³H and ³He (c) ¹²C and ¹⁴C (d) ³⁵Cl and ³⁷Cl

Answer: (b) ³H and ³He. These have different atomic numbers (1 for hydrogen and 2 for helium).

Common Misconceptions about Isotopes

Several misconceptions surround isotopes. Let's address some common ones:

• Isotopes are radioactive: While some isotopes are radioactive (radioisotopes), many are stable. Radioactivity is related to the instability of the nucleus, not simply the number of neutrons.
• Isotopes have vastly different chemical properties: While the mass difference can slightly influence reaction rates, isotopes of the same element exhibit nearly identical chemical behavior. This is because chemical properties are determined primarily by the electron configuration, which is largely unaffected by the neutron number.
• All isotopes are equally abundant: The abundance of different isotopes in nature varies significantly depending on the element and the nuclear stability of the isotopes.

Conclusion

Understanding isotopes is crucial across diverse scientific and technological fields. This article has provided a comprehensive explanation of isotopes, outlining how to identify them, differentiating them from other similar atomic species, and highlighting their significant applications. By mastering the concepts discussed here, you can confidently approach problems involving the identification and understanding of isotopes. Remember, the key is to focus on the atomic number (number of protons) to determine the element, and the mass number (protons plus neutrons) to differentiate isotopes of the same element.