In atomic and molecular chemistry, species that contain the same total number of electrons are collectively referred to by which term?

Introduction / Context:
This question belongs to the basic terminology of atomic structure and nuclear chemistry. It asks you to identify the correct term for species that have the same number of electrons. Distinguishing between isotopes, isobars, isotones and isoelectronic species is important because these terms describe different relationships between atoms or ions and are frequently tested in competitive examinations.

Given Data / Assumptions:
- The focus is on species with the same total number of electrons.
- The options include isotopes, isobars, isoelectronic and isotones.
- We assume standard textbook definitions: isotopes have same atomic number, isobars have same mass number, isotones have same number of neutrons and isoelectronic species have the same number of electrons.

Concept / Approach:
Isoelectronic species are defined as atoms, ions or molecules that contain the same number of electrons. For example, N3-, O2-, F-, Ne, Na+ and Mg2+ are all isoelectronic with 10 electrons. Isotopes, on the other hand, are atoms of the same element with the same atomic number but different mass numbers. Isobars are atoms of different elements that have the same mass number. Isotones have the same number of neutrons but different numbers of protons. Since the question explicitly refers to the same number of electrons, the correct term is isoelectronic.

Step-by-Step Solution:
Step 1: Recall the definition of isoelectronic species: entities that possess the same total number of electrons, even if they are different elements or ions. Step 2: Recall the definition of isotopes: same atomic number, different mass numbers, hence same number of protons and electrons but different neutrons. Step 3: Recall the definition of isobars: same mass number, different atomic numbers, so their electron counts usually differ. Step 4: Recall the definition of isotones: same number of neutrons, different number of protons and typically electrons. Step 5: Since the question is specifically about species containing the same number of electrons, select the term isoelectronic.

Verification / Alternative check:
To verify, consider the set of species O2-, F-, Ne and Na+. Oxygen has atomic number 8, so O2- has 10 electrons. Fluorine has 9 electrons, so F- has 10 electrons. Neon has 10 electrons, and Na+ (11 - 1) also has 10 electrons. These different atoms and ions are isoelectronic. They are not isotopes, because they have different atomic numbers. They are not isobars, because their mass numbers differ, and they are not isotones, because their neutron counts differ. This example reinforces that the correct term for same electron count is isoelectronic.

Why Other Options Are Wrong:
Isotopes: refer to same atomic number and different mass numbers, emphasising protons and neutrons rather than electrons alone.
Isobars: refer to the same mass number, not the same number of electrons.
Isotones: refer to the same number of neutrons, independent of electron count.

Common Pitfalls:
A common mistake is to confuse isoelectronic with isotopes because both sets can share similar electronic structures. However, isotopes are restricted to the same element and involve neutron differences, whereas isoelectronic species can come from different elements and charge states. Another pitfall is to mix up the prefixes iso, bar and tone. To avoid confusion, remember that isoelectronic focuses specifically on electrons, while the other terms are primarily about nuclear properties.

Final Answer:
Species containing the same number of electrons are called isoelectronic species.