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## Basic structure of an atom and atomic models, Physics tutorial

Atom:Atom is the Smallest part of the element which can take part in the chemical reaction and retains all chemical properties of that element.

:Atomic StructureThe atom is spherical in shape. It has nucleus which is positively charged and located at centre of atom. Nucleus is composed of protons and neutrons. Negative electrons move round nucleus in energy shells. Electrons are held together by strong Columbic forces. Positively charged nucleus and negatively charged electrons combined to provide the atom a neutral charge. Atoms have a radius of 10

^{-10}m and radius of nucleus is 10^{-16}m.:Charge QuantizationElectricity comprises of charges carried by protons, electrons, neutrons etc. Electric charges are of two forms: Positive and Negative. Negative charges are known as electrons and positive charges are called protons. Charge carry by both electron and proton are exactly equal but opposite.

Minimum electric charge is denoted by the symbol e, electronic charge has the magnitude of 1.6 X 10

^{-19}Coulombs.That is e = 1.6 X 10

^{-19}C.Any physical existing charge in universe is the integral multiple of e, i.e. multiple integral of e = ne, where n is any number. So charge (e) exists in discrete form and not in continuous amount. This is referred to as charge quantization.

: Is the record of chemical constituents of the substance separated according to the mass and presented as the spectrum as estimated using a mass spectrometer. One version of this device is called as Bainbridge mass spectrometer. It operates on principle that the beam of ions is made to pass through velocity selector. In velocity selector charged particles all move with the same velocity. This is attained by the combination of vertically downward electric field E that is perpendicular to the magnetic field B. In velocity selector the magnetic force is qv X B and electric field is qE. When charged particles move in straight horizontal line through fields, the magnetic force is equivalent to electric field i.e. qvB = qEMass Spectra (Singular, mass spectrum)v = E/B

Charged particles from velocity selector enter second magnetic field B

_{0}which has same direction as in velocity selector. On entering second magnetic field the ions move in semicircles of radius r before striking the photographic plate. If te ions are positively charged, beam deflects upward, and if ions are negatively charged, the beam deflects upward. Whereas in circular motion, centripetal ( F = mv^{2}/r) force is equivalent to magnetic force (qvB0)i.e. mv

^{2}/r = B_{0}qvmv/r = B

_{0}qm/q = B

_{0}r/vbut v = E/B

m/q = B

_{0}rB/EThus, we can find out m/q by estimating radius r of curvature and knowing fields B, B

_{0}, and E. In practice mass spectrometer estimate different isotopes of given ion, as ions all carry same charge q. In this way, mass ratios can be determined even if q is unknown.:IsotopesIsotopes are elements with unequal mass number but equal atomic number (or same atomic number but different neutrons number)

E.g. 1)

^{2}_{1}H,^{3}_{1}H2)

^{35}_{17}cl,^{37}_{17}cl etc.:Atomic modelsAtomic models are different pictures of atom that scientists presented how the atom looks like. Few of these models comprise:

:Bohr's model of an atom:Bohr's modelBohr's model of the atom was extensively accepted as correct model of an atom. Some of its basic revolutionary suggestions of an atom are:

Electrons can revolve round nucleus in only in certain permitted orbits and while they are in the orbits they don't emit radiations (energy). Every orbit has a fixed amount of energy (has kinetic energy because of motion and potential energy due to attraction of the nucleus.)

Allowed orbits are those for which orbital angular momentum is equal to the integral multiple of ?(? = h/2π) and h is Planck's constant. L = mvr = n? where n = 1, 2, 3, 4, ------- and n is known as principal quantum number.

The electron can jump from orbit of energy E

_{2}to another of energy E_{1}and energy difference is emitted as one quantum of radiation of frequency f provided by Planck's equation:E

_{2}- E_{1}= hf:Hydrogen SpectraThese are horizontal lines drawn one above other to symbolize energy transition (or energy levels) in increasing order in the hydrogen atom. The transition is the jump from one energy level to another. Bohr derived the formula for energy of the electron in any energy level as:

E

_{n}= -me^{4}/8ε^{2}_{0}h^{2}n^{2}Where m = mass of an electron

e = Charge of an electron

ε

_{0 }= permittivity of free space or vacuumh = Planck's constant

Recasting the above formula i.e

E

_{n}= -(me^{4}/8ε^{2}_{0}h^{2})x1/n^{2}If m = 9.1 X 10

^{-31}Kge = 1.6 X 10

^{-19}Coloumbε

_{0}= 8.85 X 10^{-12}farad per meterh = 6.6 X 10

^{-34}JsThen E

_{n}= -9(9.1 x 10^{-31})(1.6 x 10^{-19})^{4}/8(8.85 x 10^{-12})^{2}(6.6 x 10^{-34})]1/n^{2}E

_{n}= -2.179 x 10^{-18}/n^{2}JoulesBut one electron volt (1ev) = 1.6 x 10

^{-19}jouleThus energy of the electron in any energy level is:

E

_{n}= -(2.179 x 10^{-18}/1.6 X 10^{-19}) X 1/n^{2}eVE

_{n}= -13.61875/n^{2}evFor n = 1, E

_{1}= -13.62 eVFor n = 2, E

_{2}= -3.41 eVFor n = 3, E

_{3}= -1.51 eV and so on.Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)Expand your confidence, grow study skills and improve your grades.

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