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Isotopes are different forms of the same element that share the same number of protons but have a different number of neutrons. This means that the isotopes of an element have identical atomic numbers but different mass numbers. The atomic number defines the element, as it represents the number of protons in the nucleus.
Isotopes are important in nuclear chemistry because some have unique properties, such as radioactivity, which can be used in medical imaging or treatments. In this exercise, we are dealing with isotopes of radon. Radon is a noble gas with the atomic number 86, meaning each isotope of radon contains 86 protons. The variation in the number of neutrons gives rise to different isotopes, such as Rn-210, Rn-218, and Rn-222.

The atomic number of an element is a fundamental property that characterizes the element. It is equivalent to the number of protons found in the nucleus of an atom. The atomic number helps distinguish one element from another. For example, radon, with an atomic number of 86, contains precisely 86 protons in its atomic structure, irrespective of its isotopic form.
Given that protons carry a positive charge, the atomic number also dictates the amount of positive charge in the nucleus, affecting how the element interacts chemically. Understanding the atomic number is crucial in nuclear chemistry, particularly when identifying different isotopes, as the atomic number remains constant among isotopes of the same element.

The mass number of an isotope is the total count of both protons and neutrons in an atom's nucleus. Unlike the atomic number, which only counts protons, the mass number varies because it also depends on the number of neutrons, which can differ between isotopes. For example, in the radon isotopes we explored, Rn-210, Rn-218, and Rn-222, the mass number is 210, 218, and 222, respectively.
The mass number is used to distinguish between different isotopes of an element. In practical terms, to find the number of neutrons in any given isotope, you subtract the atomic number from the mass number. For instance, for radon isotopes:

• Rn-210 has 124 neutrons.
• Rn-218 has 132 neutrons.
• Rn-222 has 136 neutrons.

Understanding mass numbers helps in the study of atomic structure, nuclear reactions, and radioactivity.

Neutrons are subatomic particles found in the atomic nucleus, alongside protons. They have no electrical charge, distinguishing them from the positively charged protons. Neutrons play a critical role in stabilizing the nucleus, especially in larger atoms where positive proton repulsions need balance.
To determine the number of neutrons in an isotope, you subtract the atomic number from the mass number. In our examples of radon isotopes, the calculations show how each isotope differs in neutron count:

• For Rn-210: 210 (mass number) - 86 (atomic number) = 124 neutrons.
• For Rn-218: 218 - 86 = 132 neutrons.
• For Rn-222: 222 - 86 = 136 neutrons.

Neutrons are crucial for understanding isotope stability and are a key focus in nuclear chemistry for their role in nuclear reactions and isotope formation.