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Bohr Radius

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Last updated date: 21st Jul 2024
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What is Bohr Radius?

The Bohr radius (a0) is a physical constant, approximately equal to the maximum probable distance among the nucleus and the electron in a hydrogen atom in its ground state. It is known as after Niels Bohr, due to its position in the Bohr model of an atom.


Within the Bohr model for atomic shape, recommended by Niels Bohr in 1913, electrons orbit an important nucleus below electrostatic attraction. The authentic derivation posited that electrons have orbital angular momentum in integer multiples of the decreased Planck constant, which effectively matched the remark of discrete energy levels in emission spectra, alongside predicting a hard and fast radius for each of these levels. Within the most effective atom, hydrogen, a single electron orbits the nucleus, and its smallest feasible orbit, with the bottom strength, has an orbital radius nearly the same as the Bohr radius. (It is not precisely the Bohr radius due to the reduced mass effect. They fluctuate by approximately 0.05%.)

The Bohr model of the atom was superseded via an electron possibility cloud obeying the Schrödinger equation as posted in 1926. This is further complicated by spin and quantum vacuum results to produce fine structure and hyperfine structure. despite the fact that the Bohr radius system remains important in atomic physics calculations, because of its simple relationship with essential constants. As such, it became the unit of period in atomic units.

In Schrödinger's quantum-mechanical theory of the hydrogen atom, the Bohr radius represents the most possible value of the radial coordinate of the electron position, and therefore the maximum in all likelihood distance of the electron from the nucleus.

In atomic physics, Bohr Radius is a physical constant, expressing the maximum probable distance among the electron and the nucleus in a Hydrogen atom inside the floor state. Denoted with the aid of ao or rBohr. Because of his top position in constructing the Bohr model, This bodily constant is named after him.

Hydrogen Atom and Similar Systems

The Bohr radius including the effect of decreased mass in the hydrogen atom is given by way of the decreased mass of the electron–proton gadget (with  being the mass of proton). The use of reduced mass is a generalization of the classical -frame hassle when we are out of doors the approximation that the mass of the orbiting frame is negligible compared to the mass of the frame being orbited. Because the decreased mass of the electron–proton machine is a bit smaller than the electron mass, the "reduced" Bohr radius is barely larger than the Bohr radius ( meters).

This end result may be generalized to other systems, including positronium (an electron orbiting a positron) and muonium (an electron orbiting an anti-muon) by using the reduced mass of the system and thinking about the viable exchange fee. Typically, Bohr's model members of the family (radius, energy, and so on) can be without difficulty for these unique systems (up to lowest order) by way of genuinely changing the electron mass with the decreased mass for the machine (in addition to adjusting the fee while appropriate). For instance, the radius of positronium is approximately, because the decreased mass of the positronium machine is 1/2 the electron mass ().

A hydrogen-like atom may have a Bohr radius which frequently scales as, with  the quantity of protons inside the nucleus.

Bohr Radius Formula


ao is the Bohr radius.

me is the rest mass of electrons.

εo is the permittivity of the unfastened space

(h2π) = ħ is the reduced Planck constant.

c is the velocity of light in vacuum.

α is the quality structure constant.

e is the basic charge.

Applications and Uses:

Even though the Bohr version is not utilized in physics, the Bohr radius is incredibly useful because of its promising presence in calculating other fundamental physical constants. For example Atomic unit

The Bohr radius of the electron is one among a trio of associated units of the period, the other two being the Compton wavelength of the electron  and the classical electron radius . The Bohr radius is constructed from the electron mass , Planck's constant  and the electron value. The classical electron radius is constructed from any point of these three lengths may be written in phrases of some other the use of the simple-structure constant:

The Bohr radius is about 19,000 times bigger than the classical electron radius (i.e. the not unusual scale of atoms is angstrom, while the dimensions of debris is a femtometer). The electron's Compton wavelength is about 20 instances smaller than the Bohr radius, and the classical electron radius is about 1000 times smaller than the electron's Compton wavelength.

FAQs on Bohr Radius

1. What Do You Learn from the Bohr Model?

Bohr model taught us how electrons travel in distinct circular orbits around the nucleus. The orbits are named with the letter ‘n’, and the value of n is an integer. The transfer of electrons is possible by emitting and absorbing energy.

2. What Do You Mean By Electrostatic Attraction?

The electrostatic attraction is an attracting or repelling force that refers to long-range interaction occurring between the atoms of different particles being differently charged or uncharged. The electrostatic attraction is a stronger attraction among the atoms of the particle.

3. Write a Few Lines about Static Electricity.

Static electricity is found within or on the superficial of a material with an imbalance distribution of charge. It remains in the surface position until there is no disturbance from an outside electric current or electric discharge.

4. Calculate the Radius of the Second Bohr Orbit of Lithium-ion (Li+2) in Terms of Bohr Radius aₒ.

We know that for Lithium-ion (Li+2), the values of n and z are:

n = 2, z = 3

The formula of Bohr radius, r = a₀.n²/z 

=  a₀.(2)²/3 = 4a₀/3