Isoelectronic Species and Size Trends
Compare the sizes of isoelectronic species and relate these to nuclear charge, understanding that size decreases as nuclear charge increases for species with the same number of electrons.
Why this shows up in the exam
NEET and JEE frequently test your ability to order isoelectronic ions or atoms by size.
How NEET tests this
Practise it
These are real questions from past NEET papers that test this exact idea.
The ions O²⁻, F⁻, Na⁺, Mg²⁺ and Al³⁺ are isoelectronic. Their ionic radii show
Push further
More challenging5 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.
Consider the species: P³⁻, S²⁻, Cl⁻, Ar, K⁺, Ca²⁺. Which of the following statements about their sizes is correct?
More from Classification of Elements and Periodicity in Properties
Periodic Trends in Atomic and Ionic Size
Understand how atomic and ionic radii change across periods and down groups, including trends in atomic size, atomic volume, and the relative sizes of atoms, cations, and anions.
Periodic Trends in Metallic, Nonmetallic, and Acid-Base Character
Learn how metallic and nonmetallic character, as well as the acidic or basic nature of oxides, change across periods and down groups.
Ionization Energy and Electronic Configuration
Explore the trends in ionization energy across periods and down groups, including exceptions, and relate these to electronic configuration and stability.
Electron Gain Enthalpy and Electron Affinity
Study the trends and exceptions in electron gain enthalpy (electron affinity) across the periodic table, especially in halogens, and understand its relationship with ionization energy.
IUPAC Nomenclature of Elements
Learn the IUPAC systematic naming rules for elements, especially those with atomic number greater than 100, and understand the distinction between systematic and official names for transuranium elements.
Electronegativity and Anion Formation
Understand the concept of electronegativity, its periodic trends, and how it influences the tendency of elements to form anions, including group-wise trends.