For each of the following groups, place the atoms and ions...

For each of the following groups, place the atoms and ions in order of decreasing size. a. $\mathrm{Cu}, \mathrm{Cu}^{+}, \mathrm{Cu}^{2+}$ b. $\mathrm{Ni}^{2+}, \mathrm{Pd}^{2+}, \mathrm{Pt}^{2+}$ c. $\mathrm{O}, \mathrm{O}^{-}, \mathrm{O}^{2-}$ d. $\mathrm{La}^{3+}, \mathrm{Eu}^{3+}, \mathrm{Gd}^{3+}, \mathrm{Yb}^{3+}$ e. $\mathrm{Te}^{2-}, \mathrm{I}^{-}, \mathrm{Cs}^{+}, \mathrm{Ba}^{2+}, \mathrm{La}^{3+}$

For each of the following groups, place the atoms and ions in order of decreasing size.
a. $\mathrm{Cu}, \mathrm{Cu}^{+}, \mathrm{Cu}^{2+}$
b. $\mathrm{Ni}^{2+}, \mathrm{Pd}^{2+}, \mathrm{Pt}^{2+}$
c. $\mathrm{O}, \mathrm{O}^{-}, \mathrm{O}^{2-}$
d. $\mathrm{La}^{3+}, \mathrm{Eu}^{3+}, \mathrm{Gd}^{3+}, \mathrm{Yb}^{3+}$
e. $\mathrm{Te}^{2-}, \mathrm{I}^{-}, \mathrm{Cs}^{+}, \mathrm{Ba}^{2+}, \mathrm{La}^{3+}$

Key Concepts

Electron-Electron Repulsion

Electron-electron repulsion plays a significant role in determining the size of an atom or ion. When additional electrons are present, as in anions, increased repulsion among electrons tends to expand the electron cloud, leading to a larger radius. Conversely, removal of electrons in cations reduces these repulsive forces, allowing the electron cloud to contract.

Periodic Trends

Periodic trends help explain variations in atomic and ionic sizes. Across a period, increasing nuclear charge with little increase in electron shielding causes atomic radii to decrease, while down a group, the addition of electron shells overrides the increased nuclear charge, resulting in larger atomic and ionic sizes.

Effective Nuclear Charge

The effective nuclear charge is the net positive charge experienced by electrons after accounting for the shielding by inner electrons. This concept is crucial because it determines how tightly electrons are held; ions that have lost electrons (cations) experience a higher effective nuclear charge on the remaining electrons, resulting in a smaller radius, while ions that have gained electrons (anions) have a lower effective nuclear charge per electron, leading to a larger radius.

Atomic vs Ionic Radius

Atomic radius refers to the size of a neutral atom, whereas ionic radius pertains to that of an ion. In the formation of ions, cations typically decrease in size compared to the neutral atom due to the loss of electron-electron repulsion and a relatively unchanged nuclear charge, while anions increase in size because the addition of electrons increases electron-electron repulsion.

Isoelectronic Series

In an isoelectronic series, different species have the same number of electrons, allowing for a direct comparison of their sizes based solely on differences in nuclear charge. The species with the most protons exerts a stronger pull on the electrons and is thus smaller, whereas the one with fewer protons is larger.

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