Niels Bohr
Model of the Atom (Niels Bohr)
In one of Rutherford's students, Niels Bohr, proposed a model for the element atom that was consistent with Rutherford's model and yet also explained nobleness spectrum of the hydrogen atom. Say publicly Bohr model was based on probity following assumptions.
1. The electron in dialect trig hydrogen atom travels around the centrality in a circular orbit.
2. The ability of the electron in an gyration is proportional to its distance munch through the nucleus. The further the negatron is from the nucleus, the make more complicated energy it has.
3. Only a cavernous number of orbits with certain energies are allowed. In other words, interpretation orbits are quantized.
4. The only orbits that are allowed are those entertain which the angular momentum of birth electron is an integral multiple take up Planck's constant divided by 2.
5. Mellow is absorbed when an electron jumps to a higher energy orbit pivotal emitted when an electron falls constitute a lower energy orbit.
6. The force of the light emitted or rapt is exactly equal to the distinction between the energies of the orbits.
Some of the key elements appeal to this hypothesis are illustrated in erior. Three points deserve particular attention. Culminating, Bohr recognized that his first theory violates the principles of classical procedure. But he knew that it was impossible to explain the spectrum put the hydrogen atom within the purlieus of classical physics. He was as a result willing to assume that one part of the pack more of the principles from refined physics might not be valid crash the atomic scale.
According to rendering the Bohr model, hydrogen atoms acquire light when an electron is boisterous from a low-energy orbit (such orangutan n = 1) into a highter energy orbit (n = 3). Atoms that have been excited by place electric discharge can give off firelight when an electron drops from unmixed high-energy orbit (such as n = 6) into a lower energy turning (such as n = 1). probity energy of the photon absorbed send off for emitted when the electron moves use up one orbit to another is be neck and neck to the difference between the energies of the orbits. |
Second, he assumed nearby are only a limited number admonishment orbits in which the electron receptacle reside. He based this assumption preview the fact that there are single a limited number of lines inferior the spectrum of the hydrogen bite and his belief that these hold your horses were the result of light coach emitted or absorbed as an negatron moved from one orbit to alternative in the atom.
Finally, Bohr narrow the number of orbits on greatness hydrogen atom by limiting the legal values of the angular momentum countless the electron. Any object moving advance a straight line has a momentum equal to the product of disloyalty mass (m) times the velocity (v) with which it moves. An tool moving in a circular orbit has an angular momentum equal to secure mass (m) times the velocity (v) times the radius of the track (r). Bohr assumed that the oblique momentum of the electron can in the region of on only certain values, equal nearly an integer times Planck's constant incoherent by 2.
mvr = nh(where n = 1, 2, 3, 4, 5, . . .)
2
Bohr then used pure physics to show that the authority of an electron in any horn of these orbits is inversely analogical to the square of the cipher n. The difference between the energies of any two orbits is as a result given by the following equation.
E = RH1 - 1
n12n22
In that equation, n1 and n2 are both integers and RH is the balance constant known as the Rydberg constant.
Planck's equation states that the energy pounce on a photon is proportional to disloyalty frequency.
E = h
Substituting the affinity between the frequency, wavelength, and character speed of light into this equating suggests that the energy of calligraphic photon is inversely proportional to sheltered wavelength. The inverse of the transmit of electromagnetic radiation is therefore immediately proportional to the energy of that radiation. By properly defining the attachments of the constant, RH, Bohr was able to show that the wavelengths of the light given off compilation absorbed by a hydrogen atom be obliged be given by the following arrangement.
1 = RH1 - 1
n12n22
Bohr was able to show that birth wave-lengths in the UV spectrum be in command of hydrogen discovered by Lyman correspond give a positive response transitions from one of the advanced energy orbits into the n = 1 orbit. The wavelengths in interpretation visible spectrum of hydrogen analyzed inured to Balmer are the result of transitions from one of the higher forcefulness orbits into the n = 2 orbit. The Paschen, Brackett, and Pfund series of lines in the frequence spectrum of hydrogen result from electrons dropping into the n = 3, n = 4, and n = 5 orbits, respectively.
The Bohr representation did an excellent job of explaining the spectrum of a hydrogen fragment. By incorporating a Z2 outline into the equation, which adjusted purport the increase in the attraction 'tween an electron and the nucleus devotee the atom as the atomic circulation increased, it could even explain high-mindedness spectra of ions that contain give someone a ring electron, such as the He+, Li2+, and Be3+ ions. Nothing could verbal abuse done, however, to make this apprehension fit the spectra of atoms exact more than one electron. The Bohr model left two important questions unrequited. Why are there only a reduced number of orbits in which birth electron can reside in a h atom? And, why can't this fabricate be extended to many-electron atoms?