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Difficulty: MediumSubatomic Particles, Atomic Number, Mass Number, and Isotopy

Two naturally occurring species of chlorine are represented as 1735Cl^{35}_{17}\text{Cl} and 1737Cl^{37}_{17}\text{Cl}. Which of the following statements correctly describes the relationship between these two atoms?

  1. They are isotopes because they have the same atomic number but different mass numbers due to differing neutron counts.Answer
  2. B
    They are allotropes because they represent different structural forms of the same element in the same physical state.
  3. C
    They are isobars because they have identical mass numbers but different numbers of protons in their nuclei.
  4. D
    They are ions formed by gaining or losing electrons from the outermost valence shell.

Answer

The atoms are isotopes because they have the same atomic number (17 protons) but different mass numbers (35 and 37) resulting from different numbers of neutrons.
The statement identifying them as isotopes is correct because both species belong to chlorine with an atomic number of 17 (17 protons), but differ in mass numbers (35 and 37) due to having 18 and 20 neutrons respectively.

Step-by-Step Solution

1
Analyze the nuclide symbols 1735Cl^{35}_{17}\text{Cl} and 1737Cl^{37}_{17}\text{Cl} for atomic and mass numbers.
Both species have an atomic number Z=17Z = 17 (protons = 17). 1735Cl^{35}_{17}\text{Cl} has mass number A=35A = 35, while 1737Cl^{37}_{17}\text{Cl} has mass number A=37A = 37.
The lower subscript indicates atomic number (number of protons) and the upper superscript indicates mass number (protons + neutrons).
2
Calculate the neutron count for each nuclide.
Neutrons in 1735Cl=35−17=18^{35}_{17}\text{Cl} = 35 - 17 = 18. Neutrons in 1737Cl=37−17=20^{37}_{17}\text{Cl} = 37 - 17 = 20.
Neutron number is determined by subtracting atomic number from mass number (N=A−ZN = A - Z).
3
Classify the relationship based on chemical definitions.
Atoms of the same element (Z=17Z = 17) possessing different neutron counts and mass numbers are defined as isotopes.
Isotopy is defined specifically by identical atomic number paired with different mass numbers.

Key Concept

Isotopes are atoms of the same element with identical atomic numbers (protons) but different mass numbers (neutrons).
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Topics

Subatomic Particles, Atomic Number, Mass Number, and Isotopy

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