The key difference between isotopes and isoelectronic species lies in what they share: isotopes share the same number of protons (same element), while isoelectronic species share the same number of electrons.
Isotopes Explained
- Definition: Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number (mass number). All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.
- Protons are Key: Because isotopes of an element have the same number of protons, they exhibit almost identical chemical properties. The slight mass difference can sometimes lead to minor differences in reaction rates.
- Example: Hydrogen has three common isotopes:
- Protium (¹H): 1 proton, 0 neutrons
- Deuterium (²H): 1 proton, 1 neutron
- Tritium (³H): 1 proton, 2 neutrons
Isoelectronic Explained
- Definition: Isoelectronic species are atoms, ions, or molecules that have the same number of electrons. The term means "equal electric."
- Focus on Electrons: Isoelectronic species can have vastly different numbers of protons and neutrons. Their similar electronic configurations, however, can lead to some similarities in their chemical and physical properties.
- Example:
- O²⁻ (Oxygen ion): 8 protons + 2 extra electrons = 10 electrons
- F⁻ (Fluoride ion): 9 protons + 1 extra electron = 10 electrons
- Ne (Neon): 10 protons, 10 electrons
- Na⁺ (Sodium ion): 11 protons - 1 electron = 10 electrons
- Mg²⁺ (Magnesium ion): 12 protons - 2 electrons = 10 electrons
All the species above are isoelectronic with each other, having 10 electrons each.
Table Summarizing the Differences
| Feature | Isotopes | Isoelectronic Species |
|---|---|---|
| Definition | Same element, different # of neutrons | Different elements/ions, same # of electrons |
| Protons | Same number | Different numbers |
| Neutrons | Different numbers | Different numbers |
| Electrons | Same number | Same number |
| Chemical Props. | Very similar | Can be quite different |
In summary, isotopes are atoms of the same element with differing numbers of neutrons, whereas isoelectronic species are different atoms, ions, or molecules that possess the same number of electrons.
