Final answer:
Isotopes of an element have the same number of protons but different numbers of neutrons. The naturally occurring isotopes of argon have mass numbers 36, 38, and 40. These isotopes have the same number of protons and electrons, giving them similar chemical properties, but they differ in their atomic mass.
Step-by-step explanation:
Isotopes are different forms of the same element that have the same number of protons, but a different number of neutrons. For example, argon has three naturally occurring isotopes with mass numbers 36, 38, and 40.
This means that all three isotopes have the same atomic number, which is the number of protons in the nucleus (in the case of argon, the atomic number is 18). However, they have different mass numbers because the number of neutrons in the nucleus varies.
The similarities between the isotopes of argon are that they all have 18 protons, which gives them their chemical properties. They also have the same electron configuration, which determines how they interact with other atoms in chemical reactions. However, the isotopes differ in their atomic mass, which is the sum of the protons and neutrons in the nucleus.
Isotopes of argon occur in different proportions in nature. The most abundant isotope is argon-40, which makes up about 99.6% of all naturally occurring argon. The remaining 0.4% is made up of the other two isotopes, argon-36 and argon-38. These relative abundances are determined by the processes that form and transform atoms in stars and in the Earth's atmosphere over billions of years.