In short
The ionic radius is the size of an ion in an ionic crystal. A positive ion is smaller than its atom, and a negative ion is larger than its atom.
A cation loses electrons, so the electrons that remain are pulled more strongly by the nucleus, and the ion shrinks. An anion gains electrons, and the extra repulsion makes it swell. For ions with the same number of electrons (isoelectronic), the one with the larger nuclear charge is smaller. Down a group, ionic size rises.
and both have 10 electrons. Sodium has 11 protons and fluorine has 9, so () is smaller than ().
Also searched as: ionic size, molecule sizes.
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