Problem 47 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Isotopes of an element differ in the number of \(\ldots \ldots \ldots \ldots .\) in their nuclei.

Step-by-Step Solution

Answer

Isotopes differ in the number of neutrons in their nuclei.

Step 1: Understanding Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This means isotopes of an element share the same atomic number but have different mass numbers.

Step 2: Identifying the Difference

Since the number of protons determines the element, isotopes have the same number of protons but differ in another subatomic particle to account for the different mass numbers. The particle that varies between isotopes is the neutron.

Step 3: Concluding the Definition

Based on the understanding of isotopes, they are defined by their differing neutron count, while maintaining an identical proton count.

Key Concepts

Neutrons

Neutrons are subatomic particles found in the nucleus of an atom along with protons. Unlike protons, neutrons carry no electrical charge, making them neutral. Their primary role in the nucleus is to bind with protons, contributing to the stability of the atom. However, the number of neutrons can vary within atoms of the same element. This variation results in different isotopes.

The variation in neutron number affects the mass of the atom but not its chemical properties, since those are largely dictated by the electron configuration which is determined by the number of protons. Elements can have isotopes that are stable or radioactive, depending on their neutron-to-proton ratio. Having different numbers of neutrons allows scientists to use isotopes in various applications like radiocarbon dating and medical diagnostics.

Atomic Number

The atomic number of an element is a fundamental property that defines the element. It is equal to the number of protons found in the nucleus of an atom. Since protons carry a positive charge, the atomic number also indicates the positive charge of the nucleus.

The atomic number is crucial because it determines the element's identity and its place on the periodic table. For instance, all atoms with 6 protons are carbon, regardless of how many neutrons they contain. Each element's atomic number is unique, ensuring there is no confusion when identifying elements. The atomic number also indirectly determines the number of electrons in a neutral atom, which influence the chemical reactivity and bonds an element can form.

Mass Number

The mass number is the total count of protons and neutrons in the nucleus of an atom. It is represented as a whole number, and unlike atomic number, it is not listed on the periodic table. The mass number is significant because it gives the approximate atomic mass of an isotope in atomic mass units (amu).

While isotopes of an element share the same atomic number, their mass numbers differ due to variation in the neutron count. For example, carbon-12 and carbon-14 both have an atomic number of 6, meaning they each have 6 protons, but carbon-12 has 6 neutrons whereas carbon-14 has 8 neutrons. These mass differences, derived from the differing number of neutrons, are what distinguish isotopes from each other.