When comparing the size of different ions, the general radii...

Name: Problem 17, Chapter 8: Chemistry
Uploaded: 2023-03-08T19:55:18-08:00
Channel: Tom Comey
Description: When comparing the size of different ions, the general radii trend discussed in Chapter 7 is generally not very useful. What do you concentrate on when comparing sizes of ions to each other or when comparing the size of an ion to its neutral atom?

When comparing the size of different ions, the general radii trend discussed in Chapter 7 is generally not very useful. What do you concentrate on when comparing sizes of ions to each other or when comparing the size of an ion to its neutral atom?

Key Concepts

Coordination Environment

Ionic sizes are not measured as isolated entities but typically within a lattice or coordinated environment. The coordination number and surrounding ions or molecules can influence the effective size of an ion. Therefore, when comparing the sizes of ions or the sizes of ions to their neutral atoms, it is important to consider the structural and environmental context. This focus on the coordination sphere helps in obtaining a more accurate assessment of ionic radii than simply applying general trends from the periodic table.

Effective Nuclear Charge

This concept refers to the net positive charge that an electron experiences from the nucleus after accounting for the shielding effects of other electrons. It plays a crucial role in determining the size of an ion because a higher effective nuclear charge pulls electrons closer to the nucleus, resulting in a smaller ionic radius. When comparing ions, especially in isoelectronic series, the effective nuclear charge is a key factor since it more accurately reflects the strength of the nuclear pull on the electrons than periodic trends alone.

Isoelectronic Comparison

Comparing ions that have the same number of electrons, or are isoelectronic, is another important approach. In these comparisons, differences in ionic size are primarily attributed to the differences in nuclear charge. A greater nuclear charge in an isoelectronic series will generally result in a smaller radius. This approach allows a more precise understanding of ionic sizes than relying on general periodic trends, which may not hold true once ions have different charge distributions and electron configurations.

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