Describe Rutherford’s experiment and how it led to the structure of the atom. Wh
ID: 1004916 • Letter: D
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Describe Rutherford’s experiment and how it led to the structure of the atom. What previous experiments contributed to his knowledge that made it possible for him to form a hypothesis about the structure of the atom and test his hypothesis experimentally? Include in your answer: The cathode ray tube and contributions from J.J. Thomson, the Millikan oil drop experiment, and M. Curie and the discovery of alpha particles. b) Consider the 23Na atom. Given that the radius and mass of the nucleus are 3.04 x 10^15 m and 3.82 x 10^23 g, respectively, calculate the density of the nucleus in g/cm3. The radius of a 23Na atom is 186 pm. Calculate the density of the space occupied by the electrons in the sodium atom. Do your results support Rutherford’s model of an atom? [The volume of a sphere is (4/3)pi r^3, where r is the radius and the mass of an electron is 9.10 X 10^28 g]. Describe Rutherford’s experiment and how it led to the structure of the atom. What previous experiments contributed to his knowledge that made it possible for him to form a hypothesis about the structure of the atom and test his hypothesis experimentally? Include in your answer: The cathode ray tube and contributions from J.J. Thomson, the Millikan oil drop experiment, and M. Curie and the discovery of alpha particles. b) Consider the 23Na atom. Given that the radius and mass of the nucleus are 3.04 x 10^15 m and 3.82 x 10^23 g, respectively, calculate the density of the nucleus in g/cm3. The radius of a 23Na atom is 186 pm. Calculate the density of the space occupied by the electrons in the sodium atom. Do your results support Rutherford’s model of an atom? [The volume of a sphere is (4/3)pi r^3, where r is the radius and the mass of an electron is 9.10 X 10^28 g]. Describe Rutherford’s experiment and how it led to the structure of the atom. What previous experiments contributed to his knowledge that made it possible for him to form a hypothesis about the structure of the atom and test his hypothesis experimentally? Include in your answer: The cathode ray tube and contributions from J.J. Thomson, the Millikan oil drop experiment, and M. Curie and the discovery of alpha particles. b) Consider the 23Na atom. Given that the radius and mass of the nucleus are 3.04 x 10^15 m and 3.82 x 10^23 g, respectively, calculate the density of the nucleus in g/cm3. The radius of a 23Na atom is 186 pm. Calculate the density of the space occupied by the electrons in the sodium atom. Do your results support Rutherford’s model of an atom? [The volume of a sphere is (4/3)pi r^3, where r is the radius and the mass of an electron is 9.10 X 10^28 g].Explanation / Answer
According to the Atomic theory proposed by John Dalton ,all matter is composed of small indivisible particles called atoms.In 1833,Michael faraday showed the relationship between matter and electricity.This suggested that atom was not simple indivisible particle of matter but was made up of smaller particles.The work of J.J.Thomson and Ernest Rutherford actually laid the foundation of modern picture of atom consisting of subatomic particles like electron,proton,neutron,positron etc.
The nature and existence of electron was established by experiments on conduction of electricity through gases at extremely low pressures known as discharge tube experiments.Under ordinary conditions the gases are the poor conductor of electricity.However ,when a high voltage of the order of 10,000volts or more was applied to them at very low pressures,the gases become conductors and electricity begins to flow in the form of rays towards positive electrode.These rays are called Cathode Rays.the existence of these rays was shown by scientists like Plucker ,Crookes but main credit goes to J.J.Thomson who studied the properties of cathode rays in detail and led to the discovery of electron.He determined the ratio of the charge (e) of the electron to its mass (m) by measuring the deflection under the simultaneous influence of electric and magnetic flieds applied perpendicular to each other.
J.J.Thomson gave the following relation to calculate e/m ratio
e/m =E/ (rB2)
E= intensity of applied electric field B= intensity of applied magnetic field r=radius of circular path of e The value of e/m= 1.76*1011C/Kg
The first precise measurement of the charge on an electron was made by Robert A.MIllikan in 1909 by oil drop experiment.The charge on electron was found to be 1.6022 * 10-19 C. For an atom to be electrically neutral the existence of positively charged particle was shown by E.Goldstein. He repeated the discharge tube experiment by using perforated cathode.Th erays were attracted towards the negative plate in an elctric fieldas they were positively charged .So they were called as anode rays. The phenomenon of radiactivity was discovered by Henri Becquerel and Curie.The phenomenon of spontaneous emission of active raditions by certain elements like uranium,radium,thorium etc.is called radioactivity and the substances are called radioactive substances.the effect of the electric and magnetic fields on these radiations was studied and concluded that the radiations were split into three types of rays called as alpha rays,beta rays and gamma rays. Thomsons Atomic Model After the discovery of protons,electrons J.J.Thomson proposed a simple model for there arrangement in an atom.He proposed that the positive charge is spread in which the electrons are embedded to make the atom as a whole neutral.This model was much like a raisins in the pudding so also known as Thomsons plum pudding model.But this was discarded as it was not consistent with the result of scattering of alpha particles by thin metal foils. Rutherford's Scattering experiment In order to understand the arrangement of electrons and protons in atom Rutherford and his co-workers performed a series of experiment using alpha particles .A beam of alpha particles was directed against a thin foil of about 0.0004 cm thickness of gold,platinum ,silver or copper respectively.The foil was surrounded by a circular fluorescent ZnS screen .Whenever an alpha particle struck the screen,it produces a flash of light.The following observations were made: 1) Most of the alpha particles ( nearly 99%) went straight without any deflection. 2) A few of them got deflected through small angles.3) A ver few ( about one in 20,000) didnot pass through the foil at all and suffered large deflections ( more than 90 degree) or even come back suffering a deflection of 180 degree. Rutherford explained these observations as follows;1) Since most of the alpha particles passed through the gold foil undefflected it means that there must be a very large empty space within the atom.2) Since some of the particles are deflected to certain angle means there is a heavy positively charged mas present in the atom and it must be occupying a very small space within the atom because only few particles suffered large deflections.3) The strong deflections or even bouncing back of particles from foil ,were explained to be the direct collision with the heavy positively charged mass.the positively charged mass is called nucleus .It is supposed to be in the centre of an atom.On the basis of this experiment he propsed structure of atom in entire mass and positive charge is concentrated at centre known as nucleus .the nucleus is surrounded by negatively charged electrons which balance the positive charge on nucleus .The electrons are revolving around the nucleus at very high speed.Most of the space between nucleus and electrons is empty.
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