Vedantu’s Explanation on Band Theory
The band theory of metals is based on the valence band and conduction band. It is also known as the band theory of solids or zone theory of solids. It defines conductors, semiconductors and insulators very clearly and distinctly. Before understanding the band theory, you need to have knowledge of the following terms –
Valence Band- It is made up of those valence shell orbitals which have electrons in them. For example, a sodium valence band is made up of 3s1 orbital. The electronic configuration of sodium is 1s2, 2s2 2p6, 3s1.
Conduction Band- It is made up of those orbitals which are unoccupied by electrons either in valence shell or higher unoccupied shell. Thus, the orbitals of the conduction band are empty. Again, let’s take the example of sodium as after orbital 3s next orbital 3p is empty so it forms a conduction band.
Thus, in other words, we can say the highest energy band that is filled is known as the valence band. While the next available band in the energy structure which is empty is called the conduction band.
The band structure of sodium can be shown as follows –
Forbidden Gap – The gap or energy difference between the valence band and conduction band is called the forbidden gap.
Conductors – Those materials which allow electricity to pass through them are called conductors. Examples – copper, iron, zinc etc.
Semiconductors – Those materials which show conductivity between conductors and insulators are called semiconductors. Examples – Si, Ge, As etc.
Insulators – Those materials which do not allow electricity to pass through them are called insulators. Examples – wood, glass, stones etc. After understanding all these terms now, you are ready to understand band theory.
What is Band Theory?
In chemistry, according to the band theory of solids electrons jump from valence band to conduction band even at ordinary temperature and if this happens then the solid conducts electricity. Conductivity depends on the gap between the valence band and conduction band. If the gap or energy difference between the valence band and conduction band is more than or equal to 5ev then the material will behave as an insulator.
If the energy difference between the valence band and conduction band is equal to or less than 3ev then the material or solid is called a semiconductor. If the valence band and conduction band overlap each other then the solid is called conductors. The reasoning behind it is that electrons can jump from valence band to conduction band and thus conduct electricity. While if the gap is too much between the valence band and conduction band (more than or equal to 5ev) then electrons can’t jump from the valence band to the conduction band, hence these materials or solids can’t conduct electricity. If the valence band and conduction band are neither overlapping nor at too much distance then a few electrons may jump from the valence band to the conduction band and these materials are called semiconductors.
This was a brief of Band Theory, if you want to know more about the topic then register yourself on Vedantu or download the Vedantu learning app for classes 6-10, IITJEE and NEET.
FAQs on Band Theory
1. Why is band theory needed?
The quantum state that an electron acquires inside a metal solid is described by the band theory of solids. The number of energy levels in every molecule is different. The behavior of electrons within a molecule is well explained by band theory.
The knowledge gathered during the quantum revolution in physics was used to build Band Theory. Felix Bloch applied quantum theory to solids in 1928.
By showing possible energies for an electron in a material, band theory helps to visualize the distinction between conductor, semiconductor, and insulator.
Students can study more about the utilization of band theory with Vedantu study material where the experts have provided the complete guide to give a better understanding to students about band theory.
2. How will you explain solid classification on the basis of band theory?
Based on the distribution of electron energies in each atom, solids can be classed as conductors, insulators, or semiconductors. However, there is a gap between the bottom of the conduction band and the top of the valence band in a semiconductor or an insulator. The energy gap, also known as the bandgap, is the result of this.
The chapter on the solid-state necessitates a lot of visualizing. The theory is simple, but students often have trouble seeing all of the lattice points and atoms that fit into them in three dimensions. This chapter is only a matter of easy math and equations if you get the visualization right! The video goes over a few solid-state examples that were hand-picked.
3. What is a forbidden gap as used in the band theory?
The chapter Band theory covers many important concepts, one of them is about the forbidden energy gap. It is defined as the gap between the valence band and conduct band. The gap between the valence band and conduction band. If this gap is greater then it means valence band electrons are firmly bound to the nucleus.
You can study detailed knowledge about this with the help of Vedantu that is a one-stop solution for all your educational queries. You can get solutions for all the problems with the help of an experts’ team of Vedantu that will guide you by providing the best study material about Band theory that covers detailed knowledge for the forbidden gap.
4. What are the characteristics of insulators, conductors and semiconductors?
Vedantu helps you to get complete knowledge about the characteristics of insulators, conductors and semiconductors-
The characteristics of Insulators are: in the insulators the forbidden energy gap is large. The electrons in the Valence band are strongly linked to atoms. The forbidden energy gap value in the insulators is 10eV. As the temperature rises, some insulators may show signs of conduction. An insulator's resistivity will be on the order of 107 ohm-meter.
Characteristics of Conductors are: in the conductors, there is no forbidden gap. The valence and conduction bands become entangled. There are lots of free electrons available for conduction. Conduction is increased by a little increase in voltage. There is no concept of a hole forming because the current is generated by a continuous flow of electrons.
Characteristics of Semiconductors are: There is a very small energy gap. Ge has a forbidden gap of 0.7eV, while Si has a forbidden gap of 1.1eV. In reality, a semiconductor is neither an insulator nor a good conductor. With the increase in temperature, the conductivity of semiconductors increases. A semiconductor's conductivity will be on the order of 102 mho-meters.
5. What are the Important Terms of chapter band theory?
There are some important key phrases that students should know are:
Current- It is nothing more than the passage of electrons. Current is defined as a continuous flow of electrons or charged particles. It is denoted by the letters I or i. Amperes are the units of measurement. An alternating current AC or a direct current DC can be used.
Voltage- It's all about the change that could be made. A voltage difference is defined as a difference in potentialities between two points that are measured between those two points. It is denoted by the letter V. Volts are the unit of measurement.
Resistance- It has the property of resisting electron flow. Resistivity is the term used to describe the presence of this attribute.
Ohm's Law is a law that governs the flow of electrons
With the terms stated above, we obtain Ohm's Law, a standard law that is very important for the behavior of all electronic components. In a perfect conductor, this is the relationship between current and voltage.
The potential difference across an ideal conductor is proportional to the current flowing through it, according to Ohm's law.
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