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Difference between Bohr Model and Quantum Model

Niels Bohr proposed an atomic model to explain the drawbacks of Rutherford atomic model. The Bohr’s atomic model is also known as planetary model. Although the Bohr model does not perfectly describe the electronic configuration, yet it explains many concepts in a correct and simplified way. According to the Bohr model, electrons are subatomic particles that are present in orbits around the nucleus. On the other hand, the Quantum model describes the electrons as a wave. The Bohr model was concerned with size of the orbits only. In the Quantum model, the size of the orbit is described by principal quantum number. It is denoted as letter “n”. Hence we can say that the Bohr model was one dimensional model that used only single quantum number to describe the distribution of electrons in the atoms.

On the contrary, the Quantum model is a three dimensional model that use three different quantum numbers to describe the electronic configuration of atoms. The quantum model of atom was given by Schrödinger. He applied the de Broglie’s equation to the wave equation to describe the electronic configuration of atoms. The electronic configuration of an atom is the pattern of distribution of electrons in it. The Quantum model describes the electronic distribution of an atom by applying three quantum numbers. These quantum numbers are namely principal quantum number, angular momentum quantum number and magnetic quantum number.

The principal quantum number is concerned with size of the orbits. It represents the energy shells present around the nucleus. The main shells are namely s, p, d and f. The angular quantum number is related to the shape of the orbital. It is denoted by letter “l”. If l=0; the orbital has a spherical shape. If l=1; the orbital has polar shape and if the l = 2; the orbital is cloverleaf shaped. It goes on with shape being more complex with increasing the value of angular quantum number. The magnetic quantum number describes the orientation of orbital in space. The fourth quantum numbers satisfies the concept that no two electrons can have same sets of quantum numbers. It is referred to as spin quantum number.

The two models also differ from each other in pattern of energy distribution of electrons. According to Bohr model, energy of electrons is present in definite orbitals. Each orbital has a definite energy level. On the contrary, the Quantum model explains the energy distribution of electrons on the basis of probability concept. It does not explain presence of any definite orbital around the nucleus. According to this model, electrons can occupy a very close or far place in relation to the nucleus. It describes the orbits as a cloud of energy present around the nucleus while the Bohr model talks about presence of definite orbitals around the nucleus.

The Quantum model describes the electronic distribution of an atom in terms of its energy level, size, shape and orientation in space. According to this model, no two electrons can have the same set of all four quantum numbers.

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From Wikipedia

Bohr model

In atomic physics, the Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a quantum physics-based modification of the Rutherford model, many sources combine the two, referring to the Rutherford–Bohr model.

Introduced by Niels Bohr in 1913, the model's key success lay in explaining the Rydberg formula for the spectral emission lines of atomic hydrogen. While the Rydberg formula had been known experimentally, it did not gain a theoretical underpinning until the Bohr model was introduced. Not only did the Bohr model explain the reason for the structure of the Rydberg formula, it also provided a justification for its empirical results in terms of fundamental physical constants.

The Bohr model is a primitive model of the hydrogen atom. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate quantum mechanics, and thus may be considered to be an obsolete scientific theory. However, because of its simplicity, and its correct results for selected systems (see below for application), the Bohr model is still commonly taught to introduce students to quantum mechanics, before moving on to the more accurate but more complex valence shell atom. A related model was originally proposed by Arthur Erich Haas in 1910, but was rejected. The quantum theory of the period between Planck's discovery of the quantum (1900) and the advent of a full-blown quantum mechanics (1925) is often referred to as the old quantum theory.

Origin

In the early 20th century, experiments by Ernest Rutherford established that atoms consisted of a diffuse cloud of negatively charged electrons surrounding a small, dense, positively charged nucleus. Given this experimental data, Rutherford naturally considered a planetary-model atom, the Rutherford model of 1911 – electrons orbiting a solar nucleus – however, said planetary-model atom has a technical difficulty. The laws of classical mechanics (i.e. the Larmor formula), predict that the electron will release electromagnetic radiation while orbiting a nucleus. Because the electron would lose energy, it would gradually spiral inwards, collapsing into the nucleus. This atom model is disastrous, because it predicts that all atoms are unstable.

Also, as the electron spirals inward, the emission would gradually increase in frequency as the orbit got smaller and faster. This would produce a continuous smear, in frequency, of electromagnetic radiation. However, late 19th century experiments with electric discharges through various low-pressure gases in evacuated glass tubes had shown that atoms will only emit light (that is, electromagnetic radiation) at certain discrete frequencies.

To overcome this difficulty, Niels Bohr proposed, in 1913, what is now called the Bohr model of the atom. He suggested that electrons could only have certain classical motions:

  1. The electrons can only travel in special orbits: at a certain discrete set of distances from the nucleus with specific energies.
  2. The electrons of an atom revolve around the nucleus in orbits. These orbits are associated with definite energies and are also called energy shells or energy levels. Thus, the electrons do not continuously lose energy as they travel in a particular orbit. They can only gain and lose energy by jumping from one allowed orbit to another, absorbing or emitting electromagnetic radiation with a frequency ν determined by the energy difference of the levels according to the Planck relation:\Delta{E} = E_2-E_1=h\nu \ , where h is Planck's constant.
  3. The frequency of the radiation emitted at an orbit of period T is as it would be in classical mechanics; it is the reciprocal of the classical orbit period: \nu = {1\over T}

The significance of the Bohr model is that the laws of classical mechanics apply to the motion of the electron about the nucleus only when restricted by a quantum rule. Although rule 3 is not completely well defined for small orbits, because the emission process involves two orbits with two different periods, Bohr could determine the energy spacing between levels using rule 3 and come to an exactly correct quantum rule: the angular momentum L is restricted to be an integer multiple of a fixed unit:

L = n{h \over 2\pi} = n\hbar

where n = 1, 2, 3, ... is called the principal quantum number, and ħ = h/2Ï€. The lowest value of n is 1; this gives a smallest possible orbital radius of 0.0529 nm known as the Bohr radius. Once an electron is in this lowest orbit, it can get no closer to the proton. Starting from the angular momentum quantum rule Bohr was a


From Yahoo Answers

Question:Is a Bohr model simply two dimensional like this? http://www.cartage.org.lb/en/themes/sciences/chemistry/generalchemistry/elements/onlibeinteractive/Oxygen/b0008.gif Or is a Bohr model like this. Or is this a Sommerfeld model? http://www.humanthermodynamics.com/Atom_diagram.jpg I need help on which one to do for a Chemistry project I wanted to do a 3D model like the second one but my write up has to be on Bohr I was just confused on if the second model was a Bohr model or a Sommerfeld model. Please Help!!!!!

Answers:difference between Bohr orbit and Sommerfeld is the shape of the orbits, Bohr's is circular and sommerfeld elliptical.. the second pic is the rutherford model.. Bohr atom looks like the one in 1st pic.. but it's suppose to be in 3D.

Question:Does anybody know what the difference between the Rutherford-Bohr model and just the Bohr model is? Can you please explain it to me? Also, if you could include pictures to aid your explanation it would really help a lot! Thanks.

Answers:Rutherford' analysis of alpha particle scattering from a metal foil led to his discovery that the atom has a nucleus. In 1911, he published a model of the atom that had a small positively charged nucleus, orbited by electrons. This model was soon superseded by the Bohr model of the atom, which borrowed ideas from Rutherford's model and the nascent theory of quantised energy transfer. The Bohr model was published in 1913; he proposed that the electrons of an atom orbit in circles around a small nucleus. Furthermore, he proposed that only those orbits for which the angular momentum of the electrons were integral multiples of h/2pi were allowed. Thus his model, allowed classical 'planetary' orbits but was also quantised. His second proposal was that no electron radiated energy as long as it remained in its allotted orbit. Thus, in the Bohr model electrons only radiated energy when they moved between orbits and this energy was quantised. Plainly, this was a very simple but for all that useful model. It could predict the principle spectra of hydrogen but could not deal with line splitting, which is observed in spectrographic analysis with high resolving power. This explanation requires quantisation of the angular momentum and elliptical orbits. Next, some of the spectra suggest that electrons have quantised spin. With these modifications: an elliptical orbits, quantised angular momentum and spin for the electrons, the Bohr model becomes quite accurate for hydrogen's observed spectra. However, discrepancies can still be observed in the spectra of hydrogen and these can only be accounted for by quantum mechanical analysis. Furthermore, Bohr's model only works for a one electron atom. When many electrons orbit an atom their mutual repulsion cannot be accounted for by the Bohr model. It was found that Bohr's electron quantum jumps only occurred between particular levels and so ad hoc selection rules had to be introduced to account for these transitions. Nobody, at the time, understood why the quantum jumps were restricted the way they were. Finally, the sharp orbits for electrons, within this model, were too naive to represent reality. All of the problems faced, by this first and justly famous working theory, were resolved by the introduction of quantum mechanics in the nineteen-twenties.

Question:currently replaced? 26.the atomic number of carbon is 6. the atomic number of nitrogen is 7. the atomic number of oxygen is 8. name the isotope. 28. explain why a neutral atom can't have one proton, one neutron, and two electrons. 30. the atomic number for iron is 26. how many neutrons are in the nuclues of an iron atom with a mass number of 57? how many electrons does the iron atom have?

Answers:In answer to your first part, Bohr's model of the atom puts the electrons is specific orbits, like planets around the sun. These orbits, or shells, are only allowed a certain number of electrons each, governed by the Exclusion Principle (no two electrons in the atom are allowed to have exactly the same quantum numbers) The Bohr model was extremely useful for analyzing the hydrogen atom, but it became apparent that it contradicted another important axiom of Quantum Mechanics, The Uncertainty Principle. In Bohr's model it was possible to know the exact position and momentum of the electrons, which The Uncertainty Principle forbids! The currently accepted model of the atom doesn't consider the electrons to be little particles orbiting the nucleus. Instead, we think of them as having certain probabilities of being in a particular place at a particular time. There are some really cool equations that allow us to plot these 'volumes of probability' around the atom for different atomic 'shells'. See: http://www.wwnorton.com/college/chemistry/chemconnections/Stars/images/orbitals.jpg I hope this made some sense! :)

Question:How is Niels Bohr s model of the atom a quantum model? Are energy states within an atom discrete or continuous in the Bohr model? Are these energy states discrete or continuous in a quantum model?

Answers:use perhaps the Riemann's dzeta function

From Youtube

Quantum Mechanics: Bohr Model :Fermilab physicist, Dr. Robert Plunkett explains Quantum Theory of the Bohr Model

Bohr's Model of Atom :Check us out at www.tutorvista.com Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a quantum physics-based modification of the Rutherford model, many sources combine the two, referring to the RutherfordBohr model. Introduced by Niels Bohr in 1913, the model's key success lay in explaining the Rydberg formula for the spectral emission lines of atomic hydrogen. While the Rydberg formula had been known experimentally, it did not gain a theoretical underpinning until the Bohr model was introduced. Not only did the Bohr model explain the reason for the structure of the Rydberg formula, it also provided a justification for its empirical results in terms of fundamental physical constants. The Bohr model is a primitive model of the hydrogen atom. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate quantum mechanics, and thus may be considered to be an obsolete scientific theory. However, because of its simplicity, and its correct results for selected systems (see below for application), the Bohr model is still ...