Problem 118 - Introductory Chemistry Atoms First

Question

True or false? The \(\mathrm{O}^{2-}\) and \(\mathrm{F}^{-}\) anions have identical electron configurations. Justify your answer with Bohr diagrams and electron configuration notation.

Step-by-Step Solution

Answer

True. The O²⁻ and F⁻ anions have identical electron configurations, as both have the electron configuration 1s²2s²2p⁶. The Bohr diagrams of both anions also show the same number of electrons in each energy level, with 2 electrons in the first energy level (1s²) and 8 electrons in the second energy level (2s²2p⁶).

Step 1: 1. Electron Configuration of O²⁻ Ion

First, let's find the electron configuration for O²⁻ ion. An oxygen atom has 8 electrons, and its electron configuration is 1s²2s²2p⁴. However, the O²⁻ ion has gained 2 extra electrons, making it a total of 10 electrons. Therefore, we need to find the electron configuration with 10 electrons. 1s²2s²2p⁶ So, the electron configuration of O²⁻ anion is 1s²2s²2p⁶.

Step 2: 2. Electron Configuration of F⁻ Ion

Next, let's find the electron configuration for F⁻ ion. A fluorine atom has 9 electrons, so its electron configuration is 1s²2s²2p⁵. However, the F⁻ ion has gained 1 extra electron, making it a total of 10 electrons. Therefore, we need to find the electron configuration with 10 electrons. 1s²2s²2p⁶ So, the electron configuration of F⁻ anion is 1s²2s²2p⁶.

Step 3: 3. Comparison of Electron Configurations

Now that we have the electron configurations for both O²⁻ and F⁻ anions, let's compare them: O²⁻: 1s²2s²2p⁶ F⁻: 1s²2s²2p⁶ Both anions have the same electron configuration.

Step 4: 4. Bohr Diagrams of O²⁻ and F⁻ Anions

Next, we will represent the O²⁻ and F⁻ anions using Bohr diagrams: O²⁻: In the first energy level, there are 2 electrons (1s²). In the second energy level, there are 8 electrons (2s²2p⁶). F⁻: In the first energy level, there are 2 electrons (1s²). In the second energy level, there are 8 electrons (2s²2p⁶). Both Bohr diagrams show that the O²⁻ and F⁻ anions have the same electron configuration with the same number of electrons in each energy level.

Step 5: Conclusion

Since both the electron configuration notation and the Bohr diagrams of O²⁻ and F⁻ anions are identical, we can conclude that the statement is true: The O²⁻ and F⁻ anions have identical electron configurations.

Key Concepts

Anions

Anions are negatively charged ions that form when an atom gains one or more electrons. This gain results in a greater number of electrons compared to protons, leading to a net negative charge. The process usually occurs with non-metal elements.
Anions play a crucial role in chemical reactions and are involved in the formation of ionic bonds by attracting cations, which are positively charged ions.

• Common examples include chloride (Cl⁻), oxide (O²⁻), and fluoride (F⁻) ions.
• Anions are often larger than their neutral atoms because the added electrons increase electron-electron repulsion, expanding the electron cloud.

These ions are essential to many biological and environmental processes, making the understanding of their properties and configurations vital in the study of chemistry.

Bohr Diagrams

Bohr diagrams are a simple representation of an atom's electron configuration, showing how electrons occupy various energy levels or shells around the nucleus. Named after Niels Bohr, these diagrams help in visualizing electron distribution in atoms and ions.
The main idea is to represent electrons as rings around the nucleus. Each ring corresponds to a principal energy level, and electrons fill these rings starting from the innermost level. For example:

• The first energy level can hold up to 2 electrons.
• The second energy level can accommodate up to 8 electrons.

Bohr diagrams are especially useful for beginner chemistry students to understand how electrons are organized, and they offer insight into why atoms bond the way they do. Despite being simplified, Bohr diagrams lay the groundwork for more complex quantum models by illustrating basic electron arrangements.

O²⁻ Ion

The oxide ion (O²⁻) is formed when an oxygen atom gains two electrons. This gain brings the total to 10 electrons, matching the electron configuration of neon, a noble gas.
Normally, oxygen has an electron configuration of 1s²2s²2p⁴. Upon gaining two electrons, its configuration changes to 1s²2s²2p⁶. This adjustment results in a full outer shell, making the ion stable. From a Bohr diagram perspective:

• There are 2 electrons in the first shell.
• There are 8 electrons in the second shell.

The oxide ion's stable electron arrangement is also reflected in its decreased reactivity compared to a neutral oxygen atom. This full outer shell configuration is a driving factor for oxygen's tendency to form O²⁻ ions in various compounds.

F⁻ Ion

The fluoride ion (F⁻) forms when a fluorine atom gains one electron to achieve a full outer electron shell. Initially, fluorine has 9 electrons and its electron configuration is 1s²2s²2p⁵. By adding one more electron, it achieves the stable configuration 1s²2s²2p⁶.
This electron arrangement mirrors that of neon, ensuring stability and minimal reactivity. In a Bohr diagram:

• The first shell contains 2 electrons.
• The second shell has 8 electrons.

This stable configuration contributes to the fluoride ion's inert nature in chemical reactions, and it illustrates why halogens like fluorine tend to gain one electron to form anions, completing their octets and achieving stability.