Question
The element argon has an atomic number of 18 and an average atom mass of 39.95 mathrm(amu) . What does amu mean? Based on this information, which isotope of argon is likely the most abundant?
Answer
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Constance
Master · Tutor for 5 years
Answer
#ExplanationThe term "amu" stands for atomic mass unit. It is a standard unit of mass that quantifies mass on an atomic or molecular scale. 1 amu is defined as one-twelfth the mass of a carbon-12 atom, which is the isotope of carbon with 6 protons and 6 neutrons.Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.The atomic number of an element represents the number of protons in the nucleus. Since argon has an atomic number of 18, this means it has 18 protons. The atomic mass of an element is the weighted average mass of the atoms in a naturally occurring sample of the element. It is usually close to the mass number of the most abundant isotope, but it will not be a whole number if the element has more than one isotope.Given that the average atomic mass of argon is 39.95 amu, the most abundant isotope of argon is likely Argon-40. This is because the atomic mass is closest to 40, and when considering the atomic number of 18 (number of protons), Argon-40 (which has 22 neutrons) would make the most sense.#AnswerThe most abundant isotope of argon is likely Argon-40.