L>The Bohr Model
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 The BohrModel
The most crucial properties of atomic and also molecular structure might beexemplified making use of a simplified photo of one atom the is called the BohrModel. This design was proposed by Niels Bohr in 1915; itis not completely correct, butit has numerous features the are about correctand it is sufficient for much of our discussion. The correct theory of theatom is dubbed quantum mechanics; the Bohr design is an approximationto quantum mechanics that has actually the virtue the being much simpler.(Here is a an ext realistic conversation of what atom orbitals look like in quantummechanics.)

A Planetary design of the Atom

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The Bohr atom
The Bohr model is most likely familar as the "planetary model" that the atom shown in the adjacent figure that,for example, is supplied as a symbol because that atomic energy (a little of a misnomer, sincethe energy in "atomic energy" is actually the power of the nucleus, ratherthan the whole atom). In the Bohr model the neutrons and protons (symbolized through red and blue balls in the surrounding image) occupy adense central region dubbed the nucleus, and also the electrons orbit the nucleusmuch choose planets orbiting the sunlight (but the orbits space not confined to a planeas is around true in the Solar System). The surrounding image is no toscale since in the realistic casethe radius that the nucleus is around 100,000 times smaller than theradius of the entire atom, and as far as we can tell electrons room pointparticles there is no a physics extent.This similarity between a planetary model and also the Bohr version of the atomultimately arises due to the fact that the attractivegravitational force in a solar systemand the attractiveCoulomb (electrical) force between the positively charged nucleus andthe negatively fee electrons in an atom space mathematically of the exact same form.(The form is the same, yet the intrinsicstrength the the Coulombinteraction is much bigger than that of the gravitational interaction; inaddition, there are confident and an adverse electrical charges therefore the Coulombinteraction have the right to be one of two people attractive or repulsive, however gravitation is alwaysattractive in our existing Universe.)

But the Orbits room Quantized

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Quantized power levels in hydrogen
The basic feature that quantum mechanics that is integrated in the Bohr Modeland that is fully different from the analogous planetary version is the theenergy that the corpuscle in the Bohr atom is restricted to certain discretevalues. One claims that the power is quantized. This method that onlycertain orbits with particular radii space allowed; orbits in between simply don"texist. The surrounding figure mirrors such quantized energy levels because that the hydrogen atom.These levels space labeled through an essence n the is referred to as a quantum number.The lowest energy state is generally termed the ground state. The stateswith successively an ext energy 보다 the soil state are referred to as the very first excitedstate, the second excited state, and also so on. Beyond an energycalled the ionization potential the single electron the the hydrogen atom is nolonger bound to the atom. Climate the power levels form a continuum. In the situation ofhydrogen, this continuum starts in ~ 13.6 eV over the floor state ("eV" standsfor "electron-Volt", a usual unit of power in atomic physics).Although this behavior may it seems to be ~ strange come our mental that room trainedfrom birth bywatchingphenomena in the macroscopic world, this is the means things act in thestrange civilization of the quantum that holds persuade at the atom level.

Atomic Excitation and also De-excitation

Atoms can make transitions between the orbits allowed by quantum mechanics byabsorbing or emitting specifically the power difference between the orbits. Thefollowing figure shows an atom excitation reason by absorption of a photon andan atom de-excitation led to by emission of a photon.
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Excitation by absorption of light and de-excitation by emissions of light
In each case thewavelength that the emitted or absorbed light is specifically such the the photoncarries the energy difference between the 2 orbits.


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This energy may be calculated bydividing the product the the Planck continuous and the rate of lighthc by the wavelength of the light). Thus, an atom deserve to absorbor emit only certain discrete wavelengths (or equivalently, frequencies orenergies).