2.13. Atomic Structure: Electronic Affinity

The atomic structure is one of the fundamental concepts in the study of Chemistry. It is essential to understand how atoms are formed and how they interact to form molecules. In this chapter, we'll focus on a specific aspect of atomic structure: electron affinity.

Electronic affinity is the energy released when a neutral atom in the gaseous state gains an electron to form a negative ion. In other words, it is the energy involved in the process of adding an electron to an atom. It is a periodic property that increases from left to right in the periodic table and decreases from top to bottom in a group. This is because atoms with high electron affinity tend to gain electrons to reach a noble gas configuration.

To understand electron affinity, it is helpful to first understand the basic structure of an atom. An atom is composed of a central nucleus that contains protons and neutrons, and an electron cloud that orbits the nucleus. Electrons are organized into energy levels or shells, which are more commonly known as orbitals.

The first orbital, known as the s orbital, can hold up to two electrons. The next one, the p orbital, can hold up to six electrons. The d orbital can hold up to ten electrons, and the f orbital can hold up to fourteen electrons. Each orbital has an energy level associated with it, and electrons prefer to occupy the lowest energy orbitals first.

However, not only do electrons fill the lowest energy orbitals first, but they also prefer to fill orbitals in a way that minimizes repulsion between electrons. This is known as the Pauli exclusion principle, which states that each electron in an atom must have a unique set of quantum numbers.

When an atom gains an electron, that electron is added to the highest available energy orbital. If that orbital already contains an electron, the two electrons will pair up, which will result in additional electronic repulsion. This is what makes the energy needed to add an electron to an atom that already has a paired electron greater than the energy needed to add an electron to an atom with an empty orbital.

Electron affinity is an important property of atoms because it influences the way atoms combine to form compounds. Atoms with high electron affinity tend to gain electrons and form negative ions, while atoms with low electron affinity tend to lose electrons and form positive ions.

In short, electron affinity is a measure of the energy released when an electron is added to an atom. It's a fundamental property of atoms that influences how they combine to form compounds. Understanding electron affinity and how it relates to atomic structure is crucial to understanding chemistry on a deeper level.

We hope that this chapter has provided a clear and understandable overview of electron affinity and how it fits into atomic structure. In the next chapter, we'll explore another important aspect of atomic structure: ionization energy.

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