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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鈦�), oxide (O虏鈦�), and fluoride (F鈦�) 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 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.

The oxide ion (O虏鈦�) 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 1s虏2s虏2p鈦�. Upon gaining two electrons, its configuration changes to 1s虏2s虏2p鈦�. 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 O虏鈦� ions in various compounds.

The fluoride ion (F鈦�) 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 1s虏2s虏2p鈦�. By adding one more electron, it achieves the stable configuration 1s虏2s虏2p鈦�.
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.