Question

1. ionic radius

a) define ionic radius:
b) ionic radius of a cation is than that of the neutral atom.
c) ionic radius of an anion is than that of the neutral atom.
d) which of the following ions has the smallest ionic radius?
s²⁻ na⁺ f⁻ mg²⁺ ca²⁺

Explanation:

• a) Ionic radius is the distance from the nucleus of an ion to the outermost electron in its electron cloud. It is a measure of the size of an ion.
• b) When an atom loses electrons to form a cation, the number of electrons decreases while the nuclear charge remains the same. The remaining electrons are more strongly attracted to the nucleus, resulting in a smaller ionic radius compared to the neutral atom.
• c) When an atom gains electrons to form an anion, the number of electrons increases. The added electrons increase electron - electron repulsion, and the electron cloud expands. So, the ionic radius of an anion is larger than that of the neutral atom.
• d) For ions with the same electron - configuration (isoelectronic ions), the ion with the higher nuclear charge has a smaller ionic radius. $S^{2 - }$ has more electron shells than the others. Among $Na^{+}$, $F^{-}$, $Mg^{2+}$, they are isoelectronic ($1s^{2}2s^{2}2p^{6}$). The nuclear charges are: for $Na^{+}(Z = 11)$, $F^{-}(Z = 9)$, $Mg^{2+}(Z = 12)$. $Ca^{2+}$ has more electron shells than $Na^{+}$, $F^{-}$, $Mg^{2+}$. Using the formula for isoelectronic ions $r=\frac{k}{Z}$ (where $k$ is a constant and $Z$ is the nuclear charge), $Mg^{2+}$ has the highest nuclear charge among $Na^{+}$, $F^{-}$, $Mg^{2+}$, so it has a smaller radius than $Na^{+}$ and $F^{-}$. And compared to $S^{2 - }$ and $Ca^{2+}$ (which have more electron shells), $Mg^{2+}$ has the smallest ionic radius.

Answer:

a) The distance from the nucleus of an ion to the outermost electron in its electron cloud.
b) smaller
c) larger
d) $Mg^{2+}$