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Rutherford model - Wikipedia, the free encyclopedia

The Rutherford model or planetary model is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger-Marsden experiment in ...

Plum pudding model

The plum pudding model of the atom by J. J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus. In this model, the atom is composed of electrons (which Thomson still called "corpuscles", though G. J. Stoney had proposed that atoms of electricity be called electrons in 1894) surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively-charged "plums" surrounded by positively-charged "pudding". The electrons (as we know them today) were thought to be positioned throughout the atom, but with many structures possible for positioning multiple electrons, particularly rotating rings of electrons (see below). Instead of a soup, the atom was also sometimes said to have had a "cloud" of positive charge.

With this model, Thomson abandoned his earlier "nebular atom" hypothesis in which the atom was composed of immaterial vorticies. Now, at least part of the atom was to be composed of Thomson's particulate negative corpuscles, although the rest of the positively-charged part of the atom remained somewhat nebulous and ill-defined.

The 1904 Thomson model was disproved by the 1909 gold foil experiment, which was interpreted by Ernest Rutherford in 1911 to imply a very small nucleus of the atom containing a very high positive charge (in the case of gold, enough to balance about 100 electrons), thus leading to the Rutherford model of the atom. Finally, after Henry Moseley's work showed in 1913 that the nuclear charge was very close to the atomic number, Antonius Van den Broek suggested that atomic number is nuclear charge. This work had culminated in the solar-system-like (but quantum-limited) Bohr model of the atom in the same year, in which a nucleus containing an atomic number of positive charge is surrounded by an equal number of electrons in orbital shells.

Thomson's model was compared (though not by Thomson) to a British dessert called plum pudding, hence the name. Thomson's paper was published in the March 1904 edition of the Philosophical Magazine, the leading British science journal of the day. In Thomson's view: ... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...

In this model, the electrons were free to rotate within the blob or cloud of positive substance. These orbits were stabilized in the model by the fact that when an electron moved farther from the center of the positive cloud, it felt a larger net positive inward force, because there was more material of opposite charge, inside its orbit (see Gauss's law). In Thomson's model, electrons were free to rotate in rings which were further stabilized by interactions between the electrons, and spectra were to be accounted for by energy differences of different ring orbits. Thomson attempted to make his model account for some of the major spectral lines known for some elements, but was not notably successful at this. Still, Thomson's model (along with a similar Saturnian ring model for atomic electrons, also put forward in 1904 by Nagaoka after James C. Maxwell's model of Saturn's rings), were earlier harbingers of the later and more successful solar-system-like Bohr model of the atom.


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

Model (art)

Art models are models who pose for photographers, painters, sculptors, and other artists as part of their work of art. Art models are often paid, sometimes even professional, human subjects, who aid in creating a portrait or other work of art including such figure wholly or partially.

Models are frequently used for training art students, but are also employed by accomplished artists. The most common types of art created using models are figure drawing, figure painting, sculpture and photography. Although commercial motives dominate over aesthetics in advertising, its 'artwork' commonly employs models.

Throughout the history of Western art, drawing the human figure from living models was considered the most useful way to develop the skill of draftsmanship. In the art schoolclassroom setting, where the purpose is to learn how to draw the human form in all the different shapes, ages and ethnicity, there are no real limitations on who the model can be. In some cases, the model may pose with various props, one or more other models, animals etc., against real or artificial background, in natural or artificial light and so on.

Models for life drawing classes are often entirely nude, apart from visually non-obstructive personal items such as small jewelry and sometimes eyeglasses. In a job advertisement seeking nude models, this may be referred to as being "undraped" or "disrobed". (Alternatively, a cache-sexe may be worn. Eadward Muybridge's historic scientific studies of the male and female form in motion, for example, has examples of both usages.)

Posing

While posing, the model is expected to remain motionless, like a mannequin, except for 'moving poses'. An experienced model will not speak, wriggle, scratch, or readjust during the pose, unless confronted by an artist or instructor who doesn't believe in complete stillness and silence in poses. To accommodate the physical limitations of the model, the model and instructor or artist may agree a schedule such as 25 minutes on, 10 minutes off to relax the muscles. The model's level of experience and skill may be taken into account in determining the length of the posing session and the difficulty of the poses.

Poses generally fall into three categories: standing, seated and reclining. Within each of these there are varying levels of difficulty, so one kind is not always easier than another. Artists and life drawing instructors will often prefer poses in which the body is being exerted, for a more dynamic and aesthetically interesting subject. Common poses such as standing twists, slouched seated poses and especially the classical contrapposto are difficult to sustain accurately for any amount of time, although it is often surprising what a skilled professional model can do. Poses can range in length from several seconds to many hours. Short dynamic poses may be used for gesture drawing exercises, with the model striking a pose - which can include strenuous or precarious positions that could not be sustained for a longer pose - just long enough for the artist to quickly capture the essence of it. Active, gestural, or challenging standing poses are often scheduled at the beginning of a session when the models' energy level is highest. Short exercises in drawing classes typically run from 5 to 25 minutes. For extended poses in which the model will take one or more breaks, chalk marks and/or masking tape are often used to help the model resume the same pose. These breaks - during which the model usually wears a robe or puts on clothing - allow the model to stretch, relax and attend to other needs.

In life drawing rooms of art schools, the platform where the life model poses for the students is sometimes referred to as the dais.

Nude models

Models for life drawing classes are often entirely nude, apart from visually non-obstructive personal items such as small jewelry and sometimes eyeglasses. In a job advertisement seeking nude models, this may be referred to as being "undraped" or "disrobed". (Alternatively, a cache-sexe may be worn. Eadward Muybridge's historic scientific studies of the male and female form in motion, for example, has examples of both usages.)

In Western countries, there is generally no objection to either sex posing nude for or drawing members of the opposite sex. However, this was not always so in the past, particularly prior to the 20th century. In 1886 Thomas Eakins was famously dismissed from the Pennsylvania Academy of Fine Art for removing the loincloth from a male model in a mixed classroom. Similarly, Victorian modesty required the female model to pose nude with her face draped (illustration). European arts academies did not allow women to study the nude at all until the end of the nineteenth century. Up into the present day some rare art classes prefer male models to wear a jockstrap.

Policies vary regarding male models having an erection. Some instructors do not mind at al


From Yahoo Answers

Question:What can be said about the Rutherford model of an atom based on Newton's laws of motion, the laws of thermodynamics, and the nature of electromagnetic radiation? 1. All of these 2. The electrons are accelerating, so they would be giving off energy. 3. Continuous source of energy must be supplied to the atom. 4. Rutherford model of the atom could not work 5. None of these

Answers:Rutherfords model of the atom couldnt work.

Question:1) They show the exact location of electrons and protons 2)They show empty space between the nucleus and electrons 3)They contain electrons and protons 4)They contain energy levels for electrons which one?

Answers:2. Rutherford's model only showed that there was a nucleus, not protons. Thomson's just showed that electrons existed and that in between was empty space.

Question:a) Calculate the energy of an electron in the second Bohr orbit of a hydrogen atom. b) If the energy difference between the ground state of an atom and its excited stage is 5.4 x 10 (to the power of -19), what is the wavelength of the photon required producing this transition.

Answers:a) The energy of an electron in any orbit is given by En = -13.6/n^2 EV Therefore, energy in second orbit is E2 = - 13.6/4EV = - 3.4 EV b) delta E = 5.4 x 10^-19 (given) Using the formula delta E = hc/Wavelength Rearranging, we have wavelength = hc/deltaE =6.6x10^-34 x 3x10^8 /5.4x10^-19 = 3.66x10^-7m/s

Question:I need an IN-DETAIL description here. I need to make a model of both, but all of the pictures and descriptions I have found so far seem to look exactly the same. WHAT IS THE DIFFERENCE?

Answers:rutherford model just says that whole mass and positive charge of electron is concentrated at its nucleaus the electrons move around nucleaus in elliptical orbit in the same way as planets move around sun modern electron cloud theory says (in addition to above theory ) that trajectory of electron is impossible to determine this theory is completely based on schrodinger's equation. it tells about the most possible arrangements of electron in an atom

From Youtube

Structure of the Atom 3: The Rutherford Model :Another informative video from the Senior physics series describing the Rutherford model. More vids- www.shep.net More info- en.wikipedia.org

Rutherford's Alpha Scattering Experiment :Check us out at www.tutorvista.com Rutheford made a theoretical analysis of angles of scattering in accordance with Thomson's theory of atom and in accordance with his own theory. He assumed that atom consisted of positive charged nucleus and negative charged electrons circling around the nucleus. Then his theoretic calculations he compared with the experiment result. Alpha particles going through atom created in accordance with the "plum cake" model wouldn't be strong abberated because the electric field in that atom wouldn't be strong. In the model created by Rutheford the field is much stronger near to the nucleus, so some of alpha particles are much more abberated. The other going in the far distance to the nucleus are almost not at all abberated. The probability that any alpha particle will hit the nucleus is small but there is such a chance. The experiment showed that there are some not much abberated alpha particles but also some abberated of a very big angle (135-150 degree). That occurrence couldn't be explained by some small, added aberrations. Experimental data proved the "planetary" model of atom.