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Ch.23 - Transition Metals and Coordination Chemistry
All textbooksBrown 14th EditionCh.23 - Transition Metals and Coordination ChemistryProblem 11
Chapter 23, Problem 11

Complete the exercises below. 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 4s electrons before their 3d 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).

Verified step by step guidance
1
Step 1: Understand the concept of lanthanide contraction. The lanthanide contraction refers to the phenomenon where the atomic radii of the lanthanide series elements decrease progressively with increasing atomic number, despite having similar electron configurations.
Step 2: Analyze how lanthanide contraction affects periodic trends. The contraction is due to poor shielding of the nuclear charge by the f-electrons, leading to a stronger attraction between the nucleus and the outer electrons.
Step 3: Evaluate option (a). Consider how the atomic radii of transition metals change across a period. This trend is more related to the filling of d-orbitals and not directly explained by lanthanide contraction.
Step 4: Evaluate option (b). Consider the electron configuration of period 4 transition metals and how they lose electrons. This behavior is due to energy considerations of 4s and 3d orbitals, not lanthanide contraction.
Step 5: Evaluate option (c). Compare the radii of period 5 and period 6 transition metals. The lanthanide contraction causes the radii of period 6 transition metals to be similar to those of period 5, as the contraction offsets the expected increase in size.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lanthanide Contraction

The lanthanide contraction refers to the gradual decrease in atomic and ionic radii of the lanthanide series elements due to the poor shielding effect of the f-electrons. As the atomic number increases, the effective nuclear charge felt by the outer electrons increases, leading to a stronger attraction and smaller radii. This phenomenon affects the properties of elements in subsequent periods, particularly transition metals.
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Lanthanide Contraction

Periodic Trends in Atomic Radii

Periodic trends in atomic radii describe how the size of atoms changes across periods and down groups in the periodic table. Generally, atomic radii decrease from left to right across a period due to increased nuclear charge, which pulls electrons closer to the nucleus. Conversely, atomic radii increase down a group as additional electron shells are added, increasing the distance between the nucleus and the outermost electrons.
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Electron Configuration and Ionization

Electron configuration refers to the distribution of electrons in an atom's orbitals. In transition metals, the 4s orbital is filled before the 3d orbital, but when forming cations, the 4s electrons are lost first due to their higher energy level. This behavior is crucial for understanding the chemical properties and reactivity of transition metals, as it influences their oxidation states and bonding characteristics.
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Related Practice
Textbook Question

Which of these crystal-field splitting diagrams represents:

a. a weak-field octahedral complex of Fe³⁺ ,

b. a strong-field octahedral complex of Fe³⁺ 

c. a tetrahedral complex of Fe³⁺

d. a tetrahedral complex of Ni²⁺ (The diagrams do not indicate the relative magnitudes of ∆. ) [Find more in Section 23.6.]

Textbook Question

In the linear crystal-field shown here, the negative charges are on the z-axis. Using Figure 23.28 as a guide, predict which of the following choices most accurately describes the splitting of the d orbitals in a linear crystal-field? [Find more in Section 23.6.]