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Of Atoms and Elements

Of Atoms and Elements. Historical and Modern Perspectives. 1831: Michael Faraday. Discovery of ions Anion : negatively-charged particles Cation : positively-charged particles Science of electrolysis: splitting substances using electricity Determined that atoms were electrical in nature.

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Of Atoms and Elements

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  1. Of Atoms and Elements Historical and Modern Perspectives

  2. 1831: Michael Faraday • Discovery of ions • Anion : negatively-charged particles • Cation : positively-charged particles • Science of electrolysis: splitting substances using electricity • Determined that atoms were electrical in nature

  3. 1895: Wilhelm Roentgen • Studying glow produced from cathode rays • Noticed that the glow could be transmitted to chemically-treated paper • X-rays discovered, but not fully understood

  4. 1895: Antoine Bequerel • Photographic film fogged when placed close to samples of uranium • Required no input of energy • Graduate student Marie Curie and later her husband Pierre continued to study the phenomenon • Marie coined the term “radioactivity”

  5. 1897: Joseph John Thomson • Showed that the beam created in a cathode-ray tube was attracted to a positive plate and repelled by a negative plate • The particles were the same regardless of the material from which the ray was generated • Coined the term “electrons” for the negative particles

  6. Thomson’s Experiment Image source: http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter02/Text_Images/FG02_03.JPG

  7. Thomson’s Model • Realized that the negatively-charged particles had to be balanced by a positively-charged substance • “Plum Pudding Model” Image sourcehttp://mws.mcallen.isd.tenet.edu/mchi/ipc/ch05htm/ch05sec1.htm

  8. 1909: Robert Millikan • Received Nobel Prize in 1923 for work • Calculated mass and charge of electrons • Mass = 0.000 000 000 000 000 000 000 000 000 000 911 kg Image source: http://www.juliantrubin.com/bigten/millikanoildrop.html

  9. Millikan’s Experiment • Sprayed oil droplets into a chamber • Calculated mass of droplets by how fast they fall (gravity) • Charge 2 plates-one positive, one negative • Oil droplets acquire extra electron by friction or x-ray irradiation • Oil falls between 2 plates until it stops falling: positive charge counteracts gravity • How much energy necessary in charged plates?

  10. 1910: Ernest Rutherford • Gold foil experiment Image source: http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_04/FG04_04.JPG Image source: http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_04/FG04_05.JPG

  11. Rutherford Model • The atom had to have something very dense and positively-charged that was repelling the positive alpha particles Image source: http://encarta.msn.com/media_461517640/Models_of_the_Atom.html

  12. 1913: Neils Bohr • Built on discoveries of James Chadwick (the neutron) and Henry Moseley (atomic number = number of protons in nucleus) • Proposed an atom with distinct energy shells occupied by electrons around nucleus Image source: http://encarta.msn.com/media_461517640/Models_of_the_Atom.html Image source: http://users.zoominternet.net/~even/science.html

  13. Erwin Schrodinger: Current Model • Less structured, more uncertainty • “Electron cloud” representing where electrons are most likely to be found Image source: http://encarta.msn.com/media_461517640/Models_of_the_Atom.html

  14. What Do We Know Now?

  15. What Do We Know Now? • Structure of atoms • Nucleus: dense cluster, nearly all the atomic mass • Protons: positive charge • Neutrons: no charge • Electron cloud surrounding nucleus • Negative charge, in distinct patterns of arrangement • Description of elements • Atomic number: number of protons • Mass number: number of protons + neutrons • Atomic symbol: one or two letters

  16. What Do We Know Now? • Organization of elements • Isotopes = atoms with the same number of protons, but different numbers of neutrons • Atomic mass = average of the masses of all isotopes of an element Image source: http://faculty.weber.edu/bdattilo/shknbk/notes/time.htm

  17. What Do We Know Now? • Notation wps.prenhall.com

  18. What Do We Know Now? • Electrons orbit the nucleus in discrete energy levels • Principal quantum numbers represent energy levels • Lowest numbers closest to nucleus Electrons CANNOT park between energy levels!

  19. What Do We Know Now? • Light behaves as both waves and particles, and its behavior is due to atomic structure • Atoms in ground state can absorb energy and kick an electron up to a higher energy level • Excited state • An electron can ONLY change state if there is an available higher quantum level • Otherwise, incoming energy will not be absorbed

  20. What Do We Know Now? • Energy needed to excite an electron to a higher quantum level is very specific • Falling electrons emit photons with wavelengths equal to the amount of energy absorbed For Example…

  21. Organization of the Atom • Levels • Principal quantum number (n) • Higher number = electron energy increases • Number of electrons allowed • 2n2

  22. Organization of the Atom • Sublevels • The number of sublevels in an energy level is equal to the principal quantum number • s • p • d • f Increasing energy

  23. Organization of the Atom • Orbitals • Theoretical 3-D regions of probability • Where an electron is most likely to exist • Orbital shapes • s-orbitals: spherical • p-orbitals: dumbbell shaped (2 lobes) • All orbitals of the same type (e.g. s-orbital) have the same shape, but volume depends on energy level • Hold 2 electrons 1s 2s 2p 3p Image source: http://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_05/FG05_25.JPG

  24. Organization of the Atom • Farther from the nucleus = higher energy electrons • Filling order depends on energy

  25. Organization of Elements • Read from left to right = order of filling • Remember: large atoms will fill an s orbital of the next higher energy level before filling a d orbital

  26. Review: Atomic Organization • Atomic spectra give us clues about the organization of electrons around the nucleus • Type of energy given off corresponds to energy levels, sublevels and orbitals of electrons

  27. Organization of Elements • Electron configuration of oxygen?

  28. Organization of Elements • Alkali Metals • Group 1 (1A) on the Periodic Table • Except hydrogen, soft shiny metals with low melting points • Good conductors • React vigorously with water

  29. Organization of Elements • Alkaline Earth Metals • Group 2 (2A) on the Periodic Table • Shiny metals • Not as reactive with water as Group 1 elements

  30. Organization of Elements • Halogens • Group 17 (7A) on the Periodic Table • Strongly reactive • Form compounds with most of the elements

  31. Organization of Elements • Noble Gases • Group 8 (8A) on the Periodic Table • All gas • Highly non-reactive, seldom in combination with other elements

  32. Organization of Elements Metals, Metalloids, Non-metals

  33. Quiz Yourself • Convert 116.3 kg into mg. Record the number in regular and scientific notation. • Refer to the periodic table and name at least one element that is: • Noble gas • Alkali metal • Alkaline earth metal • Halogen • Non-metal • Metalloid • Write the full and abbreviated electron configuration of: • Silicon • Manganese • Potassium • What is the density of a piece of molybdenum that has a mass of 13.2g and a volume of 9.43mL?

  34. Quiz Answers • 116,300,000 1.163 x 108 • Noble gas = any element in group 18 (8A) on the Periodic Table • Alkali metal = any element in group 1 (1A) • Alkaline earth metal = any element in group 2 (2A) • Halogen = any element in group 17 (7A) • Non-metal = any noble gas, halogen and O, N, C, P, S, Se, I • Metalloid = B, Si, Ge, As, Sb, Te, Po, At • Full electron configuration of: • Silicon = 1s22s22p63s23p2 • Manganese = 1s22s22p63s23p64s23d5 • Potassium = 1s22s22p63s23p64s1 • 1.40 g/mL

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