anatomy of atom

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DEPT. OF NUCLEAR MEDICINE SVIMS-University, TIRUPATI. Presented by Dr.K.R.Venkata Rajesh Reddy

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“ANATOMY” OF ATOM

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History of ATOM 400–300 B.C.: Democritus Said that smallest part of matter is the atom Coined the term ATOM 300 B.C.–1800s: Aristotelian view of matter predominated . Said that matter was composed of four main elements Earth Wind Fire Water

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1802: john Dalton Said that 1.Each element is made of atoms that are alike 2.Different elements have atoms of different mass 3.Imagined atom as tiny small spheres

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1907: J. J. Thompson advanced a “plum pudding” model of the atom. Or chocolate chip cookie model. Said that Atoms are positively charged spheres with electrons embeded in them Models of the Atom

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1911: Rutherford Said that Electrons orbit around the small ,positively charged nucleus Basically, he proved that the atom has a nucleus.

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1913: Niels Bohr Said that Electrons move in specific energy levels around positive nucleus It is referred to as the "planetary model". 1916–1925: Bohr’s model was modified by Sommerfeld, Stoner, Pauli, and Uhlenbeck to better explain the emission and spectra of multielectron atoms.

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1925–1929: Born, Heisenberg, and Schr odinger describe a new field of physics in which predictions about the behavior of particles may be made from equations governing the behavior of the particle’s “wave function. Discovered the Quantum Theory The quantum theory is the most up-to-date theory of the times. Its' model of the atom explains its stability and like Bohr's Model, treats atoms as electrons surrounding a nucleus. The electrons, however, do not have a planetary orbit. Instead, the theory gives the location of an electron as a probability instead of showing it at a certain position. The easiest way to describe the differences between the allowed and prohibited positions of electrons in an atom is to think of the electron as a wave. The wave-particle duality of quantum theory allows electrons to be described as waves, instead of particles. Keep in mind that this theory may be disproved in the near future and replaced with a new model with even more complicated mathematical calculation.

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Present model of the ATOM Electron cloud model The position of electron is impossible to predict, instead it forms a cloud of negative charge.

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ATOM “fundamental building block” of matter. An atom is the smallest unit of matter that retains the chemical properties of a material. Structure of the Atom

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Basic structure of an atom Atoms are made of subatomic particles E,P,N Nucleus Protons and neutrons referred as nucleons Found in the nucleus Both have mass(p=1.6734x10-27;N=1.6747X10-27 kg) Protons carry a positive electrical charge(+1.6x10-19 coulombs) Neutrons carry no charge One unit of charge is equal to 1.602 x 10-19 coulombs Mass and energy equivalence for E,P,N

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What is binding energy? The minimum amount of energy necessary to free an electron/nucleon from an atom is known as binding energy of the electron/nucleon in that atom . (energy is measured in atomic scale eV) Binding energy increases with increase of atomic number (z) Typical binding energies are in the range of 6 million to 9 million electron volts (MeV) (approximately one thousand to one million times the electron binding force What is ionization? When an electron /nucleon absorbs sufficient energy for its removal from the atom is called ionization. What is excitation? When an electron /nucleon absorbs amount of energy that are just sufficient to move into higher unoccupied shell process is called excitation .

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Shell model of nucleus explains the existence of discrete nuclear energy states. Nucleons are arranged in spherical shells similar to electrons. Like electrons, nucleons have quantum properties including spin. The nucleus has a spin value equal to the sum of the nucleon spin values. The lowest possible arrangement of nucleons in the nucleus is known as ground state of nuclide . Nucleons in a nucleus are bound with diff binding energy. Nuclei are stable when protons=neutrons. (Even no P,N more stable then odd no P,N) How are neutrons and protons arranged inside the nucleus?

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Nuclear Forces and Stability Like charges repel : opposite charges attract How does a nucleus stay together? Strong forces is attractive force B/T P-P,P-N,N-N. Electromagnetic forces is repulsive force B/T protons only The balance between these two forces determine the stability of nuclide. When unstable radioactive.

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Plotting of #neutrons and #protons for all stable nuclides. The curve initially starts as a straight line and then slowly bends towards the Neutron no for higher atomic no. From this curve we can see for a lighter nuclide A<50 the no of protons is equal to neutrons in a stable nuclide. For heavier nuclides A>100 the no of neutrons needed for stability is much more than the no of protons. If a radionuclide lies in the upper region it contains excess of neutrons that causes un-stability of nuclide. If a radionuclide lies in lower region excess of protons that makes the radionuclide unstable.

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How are protons ,neutrons and electrons related? P,N,E #protons= Atomic number(Z) #electrons=# protons in neutral atom #protons+#neutrons=atomic mass(A) Protons dictate what the atom is (identity) Neutron helps to dictate total mass of atom Electron dictates charge of atom More than 2000 different atoms and 259 stable nuclides have been identified. Atoms grouped in more than 105 different classes. These classes are assembled in a table called the "Periodic Table of the Elements".

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NUCLEAR NOMENCLATURE

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Same no of protons isotoPes Same Atomic mass isobArs Same no of Neutrons isotoNes

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Electrons Have a negligible mass Carry a negative electrical charge (-1.6022x10-19 coulomb) Mass(9.109x10-31 kg) Orbit the nucleus with in electron shells in wave form. Electron stability Attractive coulomb forces b/t positively charged nucleus and negatively charged electrons provides stability of electrons revolving in spherical shells.

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Electrons are positioned in energy shells That surround the nucleus. principal quantum no First quantum K shell(n=1)--------2electrons L shell(n=2)--------8 electrons M shell(n=3)-------18 electrons So on….. Up to Q have identified (n=defines first is principal quantum no which defines the shell with in which the electron resides) Outermost electron shell of an atom no matter which shell it is, never contains more than 8 electrons. The electron binding energy is greatest for innermost shell K and progressively less for outermost shell.

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second quantum number is the azimuthal quantum number (l), which can be thought of as a subshell within the shell. Technically l is the angular momentum of the electron and is related to the product of the mass of the electron, its velocity, and the radius of its orbit. Each subshell is assigned a letter designation: s, p, d, f, and so on. The third number, the magnetic quantum number (ml), describes the direction of rotation of the electron and the orientation of the subshell orbit. The fourth quantum number is the spin quantum number (ms), which refers to the direction the electron spins on its axis. Both the third and fourth quantum numbers contribute to the magnetic moment (or magnetic field) created by the moving electron.

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THANK YOU