Horizontes Energéticos: Mapeando as Bandas de Energia Eletrônica em Sólidos

Energy Horizons: Mapping the Electronic Energy Bands in Solids

June 26, 2024 Luciano Bertene

In solid state physics, the concept of energy bands in solids is nothing more than a quantum mechanical symphony in which electrons, the masters of charge, play their intricate tunes. These energy bands represent the collective quantum states available to electrons in a solid, and exploring them reveals a rich spectrum of electronic behavior. From the cozy confines of insulators to the busy corridors of conductors, the arrangement of electrons in energy bands determines the electrical, optical and thermal properties of materials. In this article, we embark on a journey through the fascinating landscape of energy bands in solids, revealing their mysteries and their profound implications for our understanding of matter and the technologies that shape our modern world. Join us on our journey into this symphonic realm where the harmony of electrons orchestrates the essence of solid state physics.

First shell electrons: proximity and reactivity

A band of electronic energy in solids that orbits directly around the nucleus in the first shell is tightly bound to the heart and retains only a small amount of energy. Therefore, the first shot has the lowest energy levels – the greater the distance from the electron to the heart, the better its point. From now on, the energy levels of the outermost layer are maximum. Due to this high energy, the valence electrons in the outermost shell can be easily extracted and hence such electrons participate in chemical reactions and bind to atoms. This discussion now refers only to the electron and shell of an isolated atom.

The innermost orbit

Imagine an atom as a small solar system with the nucleus at the center and electrons orbiting around it. The first layer is the innermost orbit, closest to the nucleus. The electrons that occupy this layer are like sentinels stationed in the heart of the atom.

Proximity to power

The electrons in the first shell are tightly bound to the nucleus of the atom due to the strong electrostatic attraction between opposite charges. This bond causes these electrons to have the lowest energy levels within the atom. They are like loyal guards, firmly guarding their territory.

Low energy, low reactivity

The low energy levels of first-shell electrons significantly influence their reactivity. Due to their proximity to the nucleus, these electrons are less likely to participate in chemical reactions. Due to their low energy, they are less likely to bond with other atoms, limiting their participation in chemical bonds.

The valence shell

In contrast to the electrons in the first shell, the electrons in the outermost shell, often called the valence shell, have significantly more energy. The chemical reactivity of an atom resides mainly in the valence shell. Due to their higher energy level and greater distance from the nucleus, valence electrons easily interact with other particles, forming bonds and driving chemical reactions.

The role of first shell electrons

Although first-shell electrons are not the main actors in chemical reactions, their presence is still essential. They determine the fundamental properties of the atom and influence properties such as atom size and ionization energy. These properties, in turn, influence how a particle interacts with other particles to form molecules and compounds.

Basic structure of an atom

In a solid, atoms are close to each other. In this case, several atoms share the outer shell electrons. These electrons are therefore less strong than the force of another atom. Valence electrons are shared by forming a bond through the valence electrons of neighboring atoms. Such bonds are called covalent bonds. Therefore, under normal conditions, valence electrons are not free because neighboring atoms bind them together.

Now the valence electrons maintain maximum energy levels. As these electrons form covalent bonds, the energy levels associated with the valence electrons combine due to the coupling of the valence electrons. This inclusion creates a band of energy.

Similarly, the different energy levels of numerous electrons change in the ^first orbit, ^2nd orbit, etc. they also combine to form several energy bands.

As an alternative to the generally separate energy levels found in isolated atoms, there are closely spaced energy levels in a solid, called energy bands.

Of all the energy bands, the important energy bands are in solids

Ruffled Ribbon
conduction band
Forbidden energy gap

Ruffled Ribbon

The energy range (i.e., band) that valence electrons possess is called the valence band.

The electrons that occupy the outermost orbit or shell of an atom are called valence electrons. In a normal fraction, a valence bond has the highest energy electrons. This range can be fully or partially filled.

These valence electrons are responsible for forming atomic bonds. The number of valence electrons in an atom also determines the valence of the element of which it is an atom. For example, boron is trivalent, while Si and Ge are tetravalent, meaning they each have four valence electrons.

Resistance in the alternating current circuit

Resistance in an AC circuit refers to the resistance that a component or material offers to the flow of alternating current. Resistance in an AC circuit causes a voltage drop across the element and dissipates electrical energy in the form of heat. When an alternating voltage is applied to a circuit that contains resistive components such as resistors or conductors, a current oscillates back and forth, constantly changing direction.

Line binding

The energy range of the conduction band electrons is called the conduction band.

The electrons responsible for conducting electricity in a conductor are called conduction electrons.

Forbidden energy gap

The distance between the conduction band and the valence band in the energy band diagram is called the forbidden energy gap. It is measured in the unit electron volts (eV).

The width of the forbidden energy gap is the size of the bond of the valence electrons with the atom. The larger the energy gap, the more tightly the valence electron is bound to the nucleus.

To push an electron from the valence band to the conduction band, an external energy must be supplied that matches the prohibited energy range.

Conclusion

The importance of these energy bands goes beyond the isolated atom. In the real world, bits form complex crystalline structures that give rise to the rich range of properties that characterize materials. Electronic interactions between neighboring atoms within these structures shape the conductivity, magnetism, and optical behavior of solids, driving technological progress and scientific discovery.