Question 1

What is an isoelectronic series?

Accepted Answer

An isoelectronic series is a group of ions and atoms that have the same number of electrons. For example, O²⁻, F⁻, Na⁺, Mg²⁺, and Al³⁺ each contain 10 electrons and share the configuration 1s² 2s² 2p⁶.

Question 2

Why does ionic radius decrease in an isoelectronic series?

Accepted Answer

The electron count stays constant, but the number of protons and nuclear charge increase. The stronger nuclear attraction pulls the common electronic configuration closer to the nucleus, so the ionic radius decreases from the first member to the last.

Question 3

What is the order of ionic radii in the 10-electron series?

Accepted Answer

The correct order is O²⁻ > F⁻ > Na⁺ > Mg²⁺ > Al³⁺. Their atomic numbers are 8, 9, 11, 12, and 13 respectively, so the size decreases as nuclear charge rises.

Question 4

Which configuration is common to the 18-electron series?

Accepted Answer

P³⁻, S²⁻, Cl⁻, K⁺, and Ca²⁺ each contain 18 electrons with the configuration 1s² 2s² 2p⁶ 3s² 3p⁶. This is the same as the argon configuration.

Question 5

Is an ion with Z = 10 included in the 10-electron series?

Accepted Answer

Z = 10 corresponds to the neutral neon atom, so it is not shown as one of the five ions in the row. The listed ions are O²⁻, F⁻, Na⁺, Mg²⁺, and Al³⁺, all of which have 10 electrons.

Isoelectronic Series 3D — Same Electrons, Shrinking Clouds

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