Which is the larger species in each pair? a. Li or Li^- b. I^- or Cs^+ c. CrorCr^3+ d.

step 1 We're trying to find the larger subspecies of each pair. I have parent ions with, on their cat i

Which is the larger species in each pair? a. Li or Li^-...

Which is the larger species in each pair? \begin{equation} \text { a. }\mathrm{Li} \text { or } \mathrm{Li}^{-}\text { b. } \mathrm{I}^{-} \text { or } \mathrm{Cs}^{+} \quad \text { c. } \mathrm{Cror} \mathrm{Cr}^{3+} \quad \text { d. } \mathrm{O} \text { or } \mathrm{O}^{2-} \end{equation}

Which is the larger species in each pair?
\begin{equation}
\text { a. }\mathrm{Li} \text { or } \mathrm{Li}^{-}\text { b. } \mathrm{I}^{-} \text { or } \mathrm{Cs}^{+} \quad \text { c. } \mathrm{Cror} \mathrm{Cr}^{3+} \quad \text { d. } \mathrm{O} \text { or } \mathrm{O}^{2-}
\end{equation}

Key Concepts

Ionic Radius

Ionic radius refers to the effective size of an ion, which can differ from the size of a neutral atom due to changes in electron-electron repulsion and the balance with nuclear charge. This concept is crucial when comparing species that have either gained or lost electrons since additional electrons typically increase the size through enhanced repulsion, while removing electrons usually decreases it.

Effective Nuclear Charge

Effective nuclear charge is the net positive charge experienced by an electron in an atom or ion, taking into account the screening or shielding effects of other electrons. When an ion gains electrons (becoming an anion), the effective nuclear charge per electron decreases, often causing an expansion of the radius; in contrast, when electrons are removed (forming a cation), the effective nuclear charge increases, pulling the remaining electrons closer to the nucleus and reducing the radius.

Isoelectronic Species

Isoelectronic species are atoms or ions that contain the same number of electrons but differ in their nuclear charge. This concept is important when comparing species like a neutral atom with its charged counterpart, as a higher nuclear charge will generally result in a smaller radius among isoelectronic series, due to the stronger attraction between the nucleus and the electron cloud.

Periodic Trends in Atomic and Ionic Sizes

Periodic trends in atomic and ionic sizes allow for systematic predictions about how sizes change across the periodic table within groups and periods. Factors like electron addition, subtraction, and the resulting changes in electron-electron repulsion and effective nuclear charge dictate these trends. For example, elements and their ions typically follow a predictable pattern where anions are larger than their neutral atoms, and cations are smaller.

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