Unit 1 and 2 Notes.docx - UNIT 1 2 NOTES ATOMIC STRUCTURE The History of Atomic Structure Democritus(400 B.C A Greek philosopher the first one to think

Unit 1 and 2 Notes.docx - UNIT 1 2 NOTES ATOMIC STRUCTURE...

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ATOMIC STRUCTURE The History of Atomic Structure Democritus (400 B.C.) A Greek philosopher, the first one to think about the existence of atoms. Believed that matter was composed of tiny indivisible particles called atomos (atoms). No experimental evidence. Lavoisier (1743-1794) Worked on combustion reactions and established "Law of Consevation of Mass". First one to realize the importance of combustion supporting gas, oxygen. John Dalton (1766-1844) A meteorologist and teacher. Has supported evidence Dalton's Theory : 1) All elements are composed of extremely small, indivisible particles called atoms . 2) Atoms of the same element have identical shape, size and chemical properties . The atoms of any one element are different from those of another. 3) Atoms of different elements mix or combine in whole number ratios . 4) Chemical reactions occur when atoms seperate, join or rearrange . In a chemical reaction, atoms of 1 element never change into another. J. J. Thomson (1859-1940) - Cathode Ray Tube experiment to discover electrons In the tube was an inert gas, a positive & a negative plates . The gas particles were attacted to the postive plate => The particles must have a negative charge (electrons). "Plum Pudding Model" = atom was a positive sphere with electrons shoved into the sides of it. Ernest Rutherford - Gold Foil Experiment to discover the nucleus Shot high energy beam of positive alpha particles (= 2 protons + 2 neutrons) into gold foil. Expected results: the alpha particles would pass straight through the foil, but: _Most alpha particles went through => the atom was mostly empty space _Few particles were deflected at small angles => the atom contained something small and positive (nucleus) _Very rarely few particles were deflected at large angles => the atom contained a small, very dense and positively charge centre (nucleus). However, he could only account for half the mass of the atom. James Chadwick (1891-1974) - Alpha particles bombardment of the metal beryllium to discover neutrons
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Bohr Model of Atom: Electrons, Flame Tests and AAS _Bohr Model: electrons travel in orbits, or energy levels, around the nucleus. The further the electron is from the nucleus; the more energy it has. _Electromagnetic Spectrum: the classification of electromagnetic waves according to their frequency. _Photons : particles of light energy. Each wavelength of light has photons that have a different amount of energy. The longer the wavelength, the lower the energy of the photons. Why an element’s line spectrum can be used to identify it? When atoms are energized, their ‘excited’ electrons jump to a higher energy level. Because of the instability, the electrons will jump back down to its ground state by releasing the excess energy in the form of light. The wavelengths of the emitted light depend on the difference in energy between the ground state and the excited state. An element has its unique amount of energy in each energy level, so it only emits specific wavelengths and light color.
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  • Fall '18
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