Definition: Ionic radii refer to the size of an ion, which is influenced by the addition or removal of electrons from an atom.
Cations: Formed when electrons are removed from an atom.
Charge: Resulting ion is positive.
Removed Electron: Typically the outermost valence electron.
Anions: Formed when electrons are added to an atom.
Charge: Resulting ion is negative.
Added Electrons: Fill the next available orbital, lowest in energy.
Practice Question: Which has a larger radius, the lithium atom or the lithium cation?
Answer: The lithium atom is larger.
Explanation:
In the lithium atom, there are 3 protons pulling on 3 electrons.
In the lithium cation, there are 3 protons pulling on only 2 electrons.
Less electron-electron repulsion in the cation results in a tighter pull and a smaller radius.
Cations are always smaller than their corresponding neutral atoms.
Practice Question: Which has a larger radius, the fluorine atom or the fluoride anion?
Answer: The fluoride anion is larger.
Why?: Adding an electron increases electron-electron repulsion, causing the electrons to push apart, resulting in a larger radius for the anion compared to the neutral atom.
Anions are larger than their parent neutral atoms.
Definition: An isoelectronic series consists of atoms and ions that have the same electron configuration but different numbers of protons.
Example: Sodium cation vs. Fluoride anion.
Comparison: Fluoride anion is larger despite both having the same electron configuration as Neon because the fluoride anion has fewer protons (9) compared to sodium (11).
Trend: The more protons there are, the stronger the attractive force on the electrons, pulling them closer to the nucleus and leading to a smaller size of the ion.
Understanding the size difference between cations and anions is crucial.
Remember that trends in ionic radius are based on the interplay of electron-electron repulsion and nucleus-electron attraction.