Atoms and ions with the same number of electrons, whose size decreases as nuclear charge rises.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
Isoelectronic species are atoms and ions that have the same number of electrons, such as O2-, F-, Ne, Na+ and Mg2+, all of which have 10 electrons. Within such a series, the species with more protons has stronger nuclear attraction and is smaller. This comparison isolates the effect of nuclear charge on size, since the electron number is constant. The radius therefore falls as the atomic number rises along an isoelectronic series. Isoelectronic relationships are useful for predicting trends in ionic radii.
Key ideas: Species with the same number of electrons, such as N3-, O2-, F-, Ne, Na+, Mg2+, Al3+ (10 electrons each). Radius falls as nuclear charge rises: N3- is the largest and Al3+ the smallest. Count electrons as Z minus charge to identify the series. They share an electron configuration, but not chemistry.
Common mistakes and connections: Students order them by atomic number in the wrong direction or think they have the same radius. With same electron count, higher Z pulls more strongly, so smaller radius. Isoelectronic series are used in comparing ionization energies and in predicting the stable ion charges (elements form ions that match the nearest noble gas).
These ions all have 10 electrons, yet radius falls from 140 to 54 pm as the nuclear charge rises from 8 to 13. The interactive lesson shows this as a live animation or chart.
O2- (Z = 8), F- (Z = 9), Ne (Z = 10), Na+ (Z = 11) and Mg2+ (Z = 12) all have 10 electrons, and their radii decrease in that order.
Atoms and ions with the same number of electrons, whose size decreases as nuclear charge rises.
Isoelectronic Species is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Atomic Structure & Periodicity first: Metals Nonmetals and Metalloids, Atomic Radius, Ionic Radius.
The next topics in Atomic Structure & Periodicity are Ionization Energy and Successive Ionization Energies.
Yes. The interactive lesson includes a self-check question on Isoelectronic Species, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Isoelectronic Species is topic 85 of 115 in Atomic Structure & Periodicity.