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ATOMIC STRUCURE The beginning: 1. Dalton’s Atomic Theory – 1808 2. Thomson’s Atomic Model – 1897 3. Rutherford’s Atomic Model –1911 4. Bohr’s Atomic Model –1913 5. Quantum Mechanical Model – Useful Information: Brief Description Max Planck Radiation emitted by heating solids to various temperatures. The (1900) energy emitted by atoms or molecules is always in whole number multiples of energy of certain well-defined quantities. The word Quanta or Quantum refers to the smallest quantity of energy that can be emitted or absorbed in the form of electromagnetic radiation. E=h, where h is Planck’s constant = 6.63 x 10-34 Js Wave Vibrating disturbance by which energy is transmitted. Speed of wave depends on type of wave and the nature of medium through which the wave is traveling. James Maxwell Electromagnetic wave has an electric and magnetic field component. (1873) Both have same wavelength and frequency. Electromagnetic Range of energies, for example, ultraviolet radiation, infrared, x-rays, Spectrum radio waves, gamma rays, visible (ROYGBIV) Electromagnetic All electromagnetic waves travel at the speed of light in a vacuum. 3.0 waves x 108m/s Albert Einstein Proposed theory to explain the photoelectric effect. Einstein’s theory (1905) of light states that a beam of light behaves as a stream of particles rather than wavelike. He called the stream of particles PHOTONS. Later it was proposed that light behaves as either as waves or particles. This property is also a characteristic of all matter. Niels Bohr Atomic structure was analogues to planetary system. Studied line (1913) spectra of hydrogen in gas phase. Line spectra due to the excitation of electrons from lower energy level to a higher one. When the electron falls to a lower energy level or ground state it emits a specific amount of energy. The line spectra are not restricted to the visible range but also extend into the UV and IR range. The energies associated with electron motion in permitted orbits are fixed in value. Therefore energies are QUANTIZED. Louis De broglie If waves can behave like a stream of particles (photons) then so can an (1924) electron possess wave like properties. A particle in motion can be treated as a wave and vise versa. Brief Description Davisson, Experimentally proved that electrons possess wave-like properties. Germer, G.P Thomson Werner Heisenberg uncertainty principle states that it is impossible to know Heisenberg both the momentum (speed x mass) and position of a particle with certainty. Erwin Schrodinger (1926) Quantum Numbers Principal quantum number Angular quantum number Magnetic quantum number Electron spin quantum number Electronic configuration Pauli Exclusion principle Hund’s rule Aufbau principle Ionization energy Formulated an equation that would describe the behaviour and energies of submicroscopic particles in general. Used this equation to find the probability of locating an electron in a given volume. This led to quantum mechanics or wave mechanics model. Describe the distribution of electron in an atom Relates average distance of electron from nucleus to a particular orbital. The bigger the number the larger the orbital. Energy level (n) Sub shells. Orbital shapes (l). s, p, d, f, g, h… Orientation of orbital in space (ml). The number of orientations can be calculated using formula 2l+1 Orientation of electrons within a subshell (ms). Two electrons is the same orbital will have opposite spins due to their opposite magnetic fields. Number of electrons distributed among various atomic orbitals. No two electrons can have the same four quantum numbers. Therefore electron spins must be opposite. Most stable arrangement of electron in subshell is one with greatest number of parallel spins. Aufbau means building up in German. The process of building up the ground state structure for each atom, in order of atomic number. The energy needed to completely remove an electron from a ground state gaseous atom. Introduction to waves: You are familiar with many types of radiant energy: visible light, UV-light, X-rays, and gamma radiation. James Clerk Maxwell in 1856 proposed the existence of waves which were related to both electricity and magnetism and called them Electromagnetic waves. Some waves require a medium to travel through, for example water waves and sound waves. In a vacuum no sound waves will be heard. However, ELECTROMAGNETIC WAVES, requires no medium of transmission. Can generate electromagnetic waves by an accelerating electrically charged particles. Wavelength Amplitude Frequency Frequency: The number of waves that pass a given point in a unit time. Unit of frequency 1 Hz = 1 s-1. The velocity of a wave = wavelength x frequency The velocity of electromagnetic waves through a vacuum is 3.0 x 108 ms-1 (3.0 x 10 8 m Hz). Since we will be concentrating on the nature of electromagnetic radiation then the equation to be used is: Speed of light = frequency x wavelength