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1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

3. Ionic Compounds

Periodic Trend: Ranking Ionic Radii

3. Ionic Compounds

Periodic Trend: Ranking Ionic Radii: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

When ranking ionic radii, consider the total number of electrons; more electrons result in a larger ionic radius. For isoelectronic species, the ionic radius increases with more negative charges. For example, zinc 2+ has the largest radius due to having the most electrons, followed by nickel. To differentiate between ions with equal electrons, the charge is crucial: a more negative charge indicates a larger ionic radius. Thus, understanding electron configuration and charge is essential for predicting ionic sizes.

Ranking Ionic Radii for the elements begins with first counting their total number of electrons.

Ranking Ionic Radii

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Periodic Trend: Ranking Ionic Radii Concept 1

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Periodic Trend: Ranking Ionic Radii Concept 1 Video Summary

When ranking ionic radii, it is essential to consider the total number of electrons in the atoms or ions being compared. Generally, a greater number of electrons corresponds to a larger ionic radius. However, when dealing with isoelectronic species—atoms or ions that possess the same number of electrons—additional criteria must be applied to determine their relative sizes.

To illustrate this, consider the following example where we arrange ions in order of decreasing ionic radius. The first step involves calculating the total number of electrons for each element or ion. For instance, iron (Fe) has an atomic number of 26, meaning it has 26 electrons when neutral. If it loses 2 electrons to become Fe²⁺, it retains 24 electrons. Manganese (Mn), with an atomic number of 25, loses 1 electron to become Mn⁺¹, also resulting in 24 electrons. Nickel (Ni), with an atomic number of 28, loses 2 electrons to become Ni²⁺, leaving it with 26 electrons. Zinc (Zn), having an atomic number of 30, loses 2 electrons to become Zn²⁺, resulting in 28 electrons.

From this analysis, we can initially rank the ions based on their electron counts: Zn²⁺ (28 electrons) is the largest, followed by Ni²⁺ (26 electrons). To differentiate between Fe²⁺ and Mn⁺¹, both of which have 24 electrons, we apply the second step. For isoelectronic species, the ionic radius increases with more negative charges. Thus, since Mn⁺¹ has a less positive charge compared to Fe²⁺, it has a larger ionic radius.

In summary, when comparing ionic radii, remember that more electrons lead to a larger ionic radius. If the number of electrons is equal, the ionic radius is determined by the charge: the more negative the charge, the larger the ionic radius. This principle is crucial for understanding the behavior of ions in various chemical contexts.

Problem

Arrange the following atoms and/or ions in the order of increasing size:Br^–, Kr, Rb⁺, Sr²⁺.

Kr < Br^- < Sr²⁺ < Rb⁺

Kr < Sr²⁺ < Rb⁺ < Br^-

Sr²⁺ < Rb⁺ < Kr < Br^-

Rb⁺ < Sr²⁺ < Kr < Br^-

Br^- < Kr < Rb⁺ < Sr²⁺

Problem

Arrange the following isoelectronic series in order of decreasing radius:F^–, O^2–, Mg²⁺, Na⁺.

O^2- > F^- > Na⁺ > Mg²⁺

F^- > O^2- > Na⁺ > Mg²⁺

O^2- > F^- > Mg²⁺ > Na⁺

F^- > O^2- > Mg²⁺ > Na⁺

O^2- > Na⁺ > F^- > Mg²⁺

Problem

For an isoelectronic series of ions, the ion that is the smallest is always

The ion with the fewest protons.

The least positively charged ion.

The ion with the highest atomic number.

The ion with the most neutrons.

The ion with the most electrons.

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Here’s what students ask on this topic:

What factors determine the ionic radius of an ion?

The ionic radius of an ion is primarily determined by two factors: the total number of electrons and the charge of the ion. More electrons result in a larger ionic radius. For isoelectronic species (ions with the same number of electrons), the ionic radius increases with a more negative charge. This is because additional negative charge increases electron-electron repulsion, causing the ion to expand. Conversely, a more positive charge results in a smaller ionic radius due to increased attraction between the electrons and the nucleus.

How do you rank ionic radii for isoelectronic species?

To rank ionic radii for isoelectronic species, first ensure that the ions have the same number of electrons. Then, compare their charges. The more negative the charge, the larger the ionic radius. For example, among N^3-, O^2-, and F^-, all of which have 10 electrons, N^3- has the largest radius, followed by O^2-, and then F^-. This is because N^3- has the most negative charge, leading to greater electron-electron repulsion and a larger radius.

Why does a more negative charge result in a larger ionic radius?

A more negative charge results in a larger ionic radius because it increases electron-electron repulsion within the ion. When an ion gains electrons, the added negative charge causes the electrons to repel each other more strongly, which forces them to spread out further from the nucleus. This increased repulsion leads to an expansion of the electron cloud, thereby increasing the ionic radius.

How do you determine the ionic radius of transition metals like Fe²⁺ and Mn⁺?

To determine the ionic radius of transition metals like Fe²⁺ and Mn⁺, first calculate the total number of electrons for each ion. For Fe²⁺, iron has an atomic number of 26, so Fe²⁺ has 24 electrons. For Mn⁺, manganese has an atomic number of 25, so Mn⁺ also has 24 electrons. Since they are isoelectronic, compare their charges. Mn⁺ has a less positive charge than Fe²⁺, making Mn⁺ larger in ionic radius due to less nuclear attraction on the same number of electrons.

What is the relationship between electron configuration and ionic radius?

The electron configuration of an ion directly affects its ionic radius. Ions with more electrons generally have larger radii due to increased electron-electron repulsion. For isoelectronic species, the ionic radius is influenced by the charge: a more negative charge results in a larger radius, while a more positive charge results in a smaller radius. Understanding the electron configuration helps predict the size of the ion by considering both the number of electrons and the charge.