The atoms of different elements that contain the same number of neutrons in their nuclei, but may have different atomic numbers and mass numbers, are called what?

Introduction / Context:
In nuclear and atomic chemistry, several related terms describe specific relationships between atomic number, mass number, and neutron count. Students often encounter isotopes, isobars, and isotones and need to distinguish among them clearly. This question focuses on the situation where atoms of different elements share the same number of neutrons in their nuclei, even though their atomic numbers and mass numbers can differ. Knowing the correct term for this relationship is important for understanding nuclear stability and nuclide classification.

Given Data / Assumptions:

• We are looking at atoms of different elements, so their atomic numbers are not the same.
• These atoms have the same number of neutrons in their nuclei.
• Mass numbers may be different because mass number equals protons plus neutrons.
• The terms available include isobars, isotopes, isotones, and isoelectronic species.

Concept / Approach:
Isotopes are atoms of the same element with the same atomic number but different mass numbers, meaning they have the same number of protons but different numbers of neutrons. Isobars are atoms of different elements with the same mass number but different atomic numbers. Isotones, on the other hand, are atoms of different elements that have the same number of neutrons but different numbers of protons and usually different mass numbers. Isoelectronic species have the same number of electrons. The question describes atoms with equal neutron count but not necessarily equal atomic number or mass number, which is the definition of isotones.

Step-by-Step Solution:
Step 1: Recall that the number of neutrons in an atom is given by N = A − Z, where A is mass number and Z is atomic number. Step 2: Identify that the question mentions atoms of elements which have the same number of neutrons, so N is the same for all such atoms. Step 3: Recognise that the atoms belong to different elements, so their atomic numbers Z are different. Step 4: Match this description to the term isotones, which refers to nuclides that share the same neutron number but have different proton numbers. Step 5: Confirm that isotopes and isobars do not fit this description because they relate to equal atomic number and equal mass number respectively, not equal neutron count.

Verification / Alternative check:
Consider two specific nuclides, for example carbon 14 and nitrogen 15. Carbon 14 has atomic number 6 and mass number 14, so it has 8 neutrons. Nitrogen 15 has atomic number 7 and mass number 15, also giving 8 neutrons. These two nuclides belong to different elements but share the same neutron count, so they are classic examples of isotones. By contrast, isotopes would be pairs like carbon 12 and carbon 14, which share atomic number 6 but have different neutron numbers. This comparison confirms that equal neutron number across different elements corresponds to isotones.

Why Other Options Are Wrong:
Isobars are nuclides that have the same mass number A but different atomic numbers Z, so they may not have the same number of neutrons. Isotopes are nuclides of the same element with the same atomic number Z but different mass numbers, which means they differ in neutrons rather than share neutron count. Isoelectronic species are ions or atoms with the same number of electrons, which is a different concept independent of neutron count. The option "None of these" is incorrect because the specific term isotones does exist and matches the description in the question.

Common Pitfalls:
Students often mix up isotopes, isobars, and isotones because the terms sound similar. A typical mistake is to choose isotopes whenever they see a question about similar nuclear properties, forgetting that isotopes must belong to the same element. Another error is to think that isobars and isotones are interchangeable. A helpful memory aid is to remember that all three words start with "iso" meaning same, and the second part hints at what is the same: "topes" refers to place in the periodic table (same atomic number), "bars" refers to mass (same mass number), and "tones" can be linked to neutrons. Using this association will help you select the right term.

Final Answer:
Atoms of different elements that have the same number of neutrons are called isotones.