One way in which Earth's evolution as a planet can be understood is by measuring the amounts of certain isotopes in rocks. One quantity recently measured is the ratio of \({ }^{129} \mathrm{Xe}\) to \({ }^{130}\) Xe in some minerals. In what way do these two isotopes differ from one another? In what respects are they the same?

Isotopes are different forms of a single chemical element, having the same number of protons but differing in the number of neutrons present in their atomic nucleus.

Xenon is element number 54 in the periodic table, which means that it has 54 protons in its nucleus. For \({ }^{129}\mathrm{Xe}\) isotope: - Number of protons (Z) = 54 - Mass number (A) = 129 - Number of neutrons (N) = A - Z = 129 - 54 = 75 For \({ }^{130}\mathrm{Xe}\) isotope: - Number of protons (Z) = 54 - Mass number (A) = 130 - Number of neutrons (N) = A - Z = 130 - 54 = 76

The main difference between \({ }^{129}\mathrm{Xe}\) and \({ }^{130}\mathrm{Xe}\) is the difference in the number of neutrons present in their nuclei. \({ }^{129}\mathrm{Xe}\) has 75 neutrons, while \({ }^{130}\mathrm{Xe}\) has 76 neutrons. This difference in the number of neutrons results in slightly different atomic masses and physical properties.

The isotopes \({ }^{129}\mathrm{Xe}\) and \({ }^{130}\mathrm{Xe}\) have the same number of protons (54) and therefore the same chemical properties. Both isotopes belong to the same element, Xenon, and have the same electron configuration, as the number of electrons is also the same (54). This means that both isotopes exhibit similar chemical behavior and reactivity. In conclusion, \({ }^{129}\mathrm{Xe}\) and \({ }^{130}\mathrm{Xe}\) isotopes differ in the number of neutrons present in their nuclei, resulting in slightly different atomic masses and physical properties. However, they have the same number of protons and electrons, and therefore share the same chemical properties and electron configuration, which makes them chemically indistinguishable.