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Chapter 23: Problem 6

The metallic radii of \(\mathrm{Ni}\), \(\mathrm{Pd}\), and \(\mathrm{Pt}\) are \(125,138,\) and \(139 \mathrm{pm},\) respectively. Why is the difference in radius between Pt and Pd so much less than between Pd and Ni?

Short Answer

Expert verified
The difference in atomic radius between Pt and Pd is much less than between Pd and Ni due to the lanthanide contraction, which results from an increase in effective nuclear charge and decrease in atomic size due to poor shielding of the nucleus by 4f electrons.

Step by step solution

01

Understand the Periodic Trends

The atomic radius of an element generally increases down a group and decreases across a period from left to right. This is due to the increase in the number of electron shells and effective nuclear charge respectively.
02

Analyze the Electron Configurations

The electron configurations are as follows: \n- Nickel (Ni) has the electron configuration [Ar] 3d8 4s2.\n- Palladium (Pd) has the unusual electron configuration [Kr] 4d10 5s0. Even though we would expect it to have 5s1, it fully occupies the d orbital instead.\n- Platinum (Pt) has the electron configuration [Xe] 4f14 5d9 6s1. It has one more d electron and one more f electron compared to Pd.
03

Relate the Trends with Configurations

The lesser increase in radius from Pd to Pt compared to Ni to Pd can be attributed to the lanthanide contraction, which is the greater-than-expected decrease in ionic radii of the elements in the lanthanide series (57–71), including the elements in period 6, like Pt. This is due to the poor shielding of the nucleus by 4f electrons, causing an increase in effective nuclear charge and decrease in atomic size.

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Most popular questions from this chapter

A 0.589 g sample of pyrolusite ore (impure \(\mathrm{MnO}_{2}\) ) is treated with \(1.651 \mathrm{g}\) of oxalic acid \(\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right)\) in an acidic medium (reaction 1). Following this, the excess oxalic acid is titrated with \(30.06 \mathrm{mL}\) of \(0.1000 \mathrm{M}\) \(\mathrm{KMnO}_{4}\) (reaction 2). What is the mass percent of \(\mathrm{MnO}_{2}\) in the pyrolusite? The following equations are neither complete nor balanced. (1) \(\quad \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+\mathrm{MnO}_{2}(\mathrm{s}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{g})\) (2) \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+\mathrm{MnO}_{4}^{-}(\mathrm{aq}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{g})\)

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