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Chapter 23: Problem 11

The lanthanide contraction explains which of the following periodic trends? (a) The atomic radii of the transition metals first decrease and then increase when moving horizontally across each period. (b) When forming ions the period 4 transition metals lose their \(4 s\) electrons before their \(3 d\) electrons. (c) The radii of the period 5 transition metals (Y-Cd) are very similar to the radii of the period 6 transition metals (Lu-Hg).

Short Answer

Expert verified
The lanthanide contraction explains the periodic trend given in option (c), where the radii of the period 5 transition metals (Y-Cd) are very similar to the radii of the period 6 transition metals (Lu-Hg).

Step by step solution

01

Option (a) Analysis

Here, we are given a trend regarding the atomic radii of transition metals decreasing and then increasing when moving across each period. The lanthanide contraction specifically affects elements in the lanthanide series and, as a result, neighboring elements in the d-block. This trend doesn't appear to directly involve the lanthanide contraction.
02

Option (b) Analysis

This option states that when forming ions, period 4 transition metals lose their 4s electrons before their 3d electrons. This trend is related to electron configurations and ionization energies, not the lanthanide contraction. Thus, this trend cannot be explained by the lanthanide contraction.
03

Option (c) Analysis

This option presents a trend where the radii of period 5 transition metals (Y-Cd) are very similar to the radii of the period 6 transition metals (Lu-Hg). We know that the lanthanide contraction causes a decrease in atomic radius across the lanthanide series. Consequently, the elements immediately following the lanthanides (in period 6) are expected to have a smaller atomic radius than one would expect without the lanthanide contraction. This trend involves the decrease in atomic radii across periods due to the lanthanide contraction and seems to be directly related.
04

Conclusion

Based on the analysis, we can conclude that the lanthanide contraction best explains the periodic trend given in option (c), where the radii of the period 5 transition metals (Y-Cd) are very similar to the radii of the period 6 transition metals (Lu-Hg).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Periodic Trends
Periodic trends are a set of patterns observed in the periodic table as we move across periods (rows) and down groups (columns). These trends help predict the behaviors and properties of elements based on their position in the table. Such trends include:
  • Atomic size or radii
  • Ionization energy
  • Electronegativity
  • Electron affinity
For example, ionization energy generally increases across a period as the atomic number rises, making it harder to remove an electron. Likewise, atomic radii tend to decrease across a period due to the increase in positive charge in the nucleus, which pulls electrons closer. Understanding these key trends is crucial for recognizing how elements will interact chemically.
Atomic Radii
Atomic radii refer to the size of an atom, specifically the distance from the nucleus to the outermost shell of electrons. This size can be influenced by several factors:
  • Number of electron shells (energy levels)
  • Nuclear charge (more protons pull electrons closer)
The lanthanide contraction plays a significant role in the atomic radii of transition metals. It causes a reduction in size across the lanthanide series, which subsequently impacts the surrounding elements. Due to the lanthanide contraction, elements in period 6 have anomalously small atomic radii, making them quite similar to elements in the preceding period.
Transition Metals
Transition metals, found in the d-block of the periodic table, have some unique properties due to their electron configurations. These metals include familiar elements like iron, copper, and gold. Key characteristics include:
  • Variable oxidation states
  • Formation of colorful compounds
  • High melting and boiling points
In the context of lanthanide contraction, the similarities in atomic radii between period 5 and period 6 transition metals become apparent. Without the contraction, period 6 metals would be significantly larger, but their size is compressed due to the shrinking effect seen across the lanthanide series. As a result, understanding these details about transition metals helps clarify trends in chemical reactivity and bonding.

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Most popular questions from this chapter

Four-coordinate metals can have either a tetrahedral or a square-planar geometry; both possibilities are shown here for \(\left[\mathrm{Pt} \mathrm{Cl}_{2}\left(\mathrm{NH}_{3}\right)_{2}\right] .(\mathbf{a})\) What is the name of this molecule? (b) Would the tetrahedral molecule have a geometric isomer? (c) Would the tetrahedral molecule be diamagnetic or paramagnetic? (d) Would the square- planar molecule have a geometric isomer? (e) Would the square-planar molecule be diamagnetic or paramagnetic? (f) Would determining the number of geometric isomers help you distinguish between the tetrahedral and square-planar geometries? (g) Would measuring the molecule's response to a magnetic field help you distinguish between the two geometries? [Sections \(23.4-23.6]\)

Crystals of hydrated chromium(III) chloride are green, have an empirical formula of \(\mathrm{CrCl}_{3} \cdot 6 \mathrm{H}_{2} \mathrm{O},\) and are highly soluble, (a) Write the complex ion that exists in this compound. (b) If the complex is treated with excess \(\mathrm{AgNO}_{3}(a q)\), how many moles of AgCl will precipitate per mole of \(\mathrm{CrCl}_{3} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) dissolved in solution? (c) Crystals of anhydrous chromium(III) chloride are violet and insoluble in aqueous solution. The coordination geometry of chromium in these crystals is octahedral, as is almost always the case for \(\mathrm{Cr}^{3+}\). How can this be the case if the ratio of \(\mathrm{Cr}\) to Cl is not \(1: 6 ?\)

For each of the following pairs, identify the molecule or ion that is more likely to act as a ligand in a metal complex: (a) carbonic acid \(\left(\mathrm{H}_{2} \mathrm{CO}_{3}\right)\) or carbonate \(\left(\mathrm{CO}_{3}^{2-}\right),(\mathbf{b})\) water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) or hydronium ion \(\left(\mathrm{H}_{3} \mathrm{O}^{+}\right),(\mathbf{c})\) phosphine \(\left(\mathrm{PH}_{3}\right)\) or phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\).

The most important oxides of iron are magnetite, \(\mathrm{Fe}_{3} \mathrm{O}_{4}\), and hematite, \(\mathrm{Fe}_{2} \mathrm{O}_{3} .\) (a) What are the oxidation states of iron in these compounds? (b) One of these iron oxides is ferrimagnetic, and the other is antiferromagnetic. Which iron oxide is more likely to be ferrimagnetic? Explain.

Draw the crystal-field energy-level diagrams and show the placement of \(d\) electrons for each of the following: (b) \(\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\), (a) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (four unpaired electrons), (a high-spin complex), (c) \(\left[\mathrm{Ru}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{2+}\) (a low-spin complex), (d) \(\left[\mathrm{IrCl}_{6}\right]^{2-}\) (a low-spin complex), (e) \(\left[\mathrm{Cr}(\mathrm{en})_{3}\right]^{3+}\), (f) \(\left[\mathrm{NiF}_{6}\right]^{4-}\).
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