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The arrangement of molecules in gases is not very close, that is, they are widely apart and loosely packed. In liquids, the molecular arrangement is moderate, meaning that the molecules are a bit apart. When it comes to solids, the molecules are so closely packed or structured that electrons (subatomic particles with a negative electric charge) gravitate into the orbitals of the atoms around them. As a result, when the atoms come together, the electron orbitals overlap. The creation of energy bands, rather than single energy levels, will result from the intermixing of atoms in solid-state objects. The Energy Bands are a collection of energy levels that are densely or tightly packed.
Formation of Energy Band
An isolated atom’s electrons have a set amount of energy in each orbit. The energy level of the outermost orbit electrons in solids, on the other hand, is impacted by the atoms close. When two isolated charges are placed near together, the electrons in the outermost orbit sense an attractive attraction from the closest or neighbouring atomic nucleus.
As a result, electron energies will not be equal, and electron energy levels will be changed to a value that is more or lower than the electron’s initial energy level. In contrast, the energy of inner orbit electrons is unaffected by the presence of adjacent atoms.
Electrons in the same orbit have different energy levels. The term “energy band” relates to the way these various energy levels are classified.
Theory of Energy Bands
Every atom’s shell, according to Bohr’s theory, has a finite quantity of energy at various levels. The interaction of electrons between the outermost and innermost shells is explained by energy band theory. According to energy band theory, there are three distinct energy bands:
- Valence band
- Forbidden energy gap
- Conduction band
Energy Bands Classification
Valence Band
Valence electrons are the electrons in the outermost shell. The valence electrons form the valence band, an energy band with a variety of energy levels. The valence band has the most energy occupied.
Conduction Band
Because the valence electrons are weakly connected to the nucleus, even at room temperature, a few of them depart the outermost orbit and become free electrons. Free electrons are referred to as conduction electrons due to their ability to conduct current in conductors. The conduction band has the lowest occupied energy levels and includes conduction electrons.
Forbidden Energy Gap
The forbidden gap is the region between the valence and conduction bands. As the name indicates, the forbidden gap has no energy and no electrons remain in this band. If the forbidden energy gap is larger, the valence band electrons are securely bound or firmly connected to the nucleus. We’ll need a certain quantity of external energy to fill the restricted energy gap.
Types of Energy Bands
There are three different types of energy bands:
- Insulators
- Conductors
- Semiconductors
Insulators
Insulators are substances or materials that do not conduct or allow electricity to travel through them. The insulators’ restricted energy gap is large enough to prevent electricity from flowing through. Rubber and wood are two examples of insulators.
Conductors
The conductor is a material in which the prohibited energy gap, such as the valence band, vanishes and the conduction band approaches the point where the two bands partially overlap. The most common conductors are gold, aluminium, copper, and gold. The quantity of free electrons accessible at room temperature is huge.
Semiconductors
Semiconductors are materials or substances with conductivity in the range of conductors to insulators. In semiconductors, the forbidden energy gap is very small, and electricity can only be transmitted if external energy is provided. To mention a few, semiconductors include germanium and silicon.
Conclusion
Solids, liquids, and gases all have distinct molecular arrangements. They are organised tightly in solids such that the electrons within the molecule atoms travel into the orbital of the surrounding atoms. In gases, the molecular organisation is complex, but in liquids, it is modest. As a result, as the atoms approach one other, the electron orbitals partially cover them. The levels of energy bands are produced as a result of the merging of atoms inside materials, rather than single energy levels. An energy band is a cluster of closely packed energy levels.
