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Schrodinger Bohr Rutherford + Thomson Democritus & Dalton Unit 3 The History of the ATOM and Atomic Structures + Democritus 460-370 B.C. Greek Philosopher He called nature’s basic particle an atomos, based on the Greek word “indivisible.” Had no evidence, so people didn’t take him seriously. He considers education to be the noblest of pursuits, but cautioned that learning without sense leads to error. (THERE MUST BE A POINT!!!) Aristotle said empty space did not exist & rejected Democritus; said matter was EARTH, WATER, AIR & FIRE + John Dalton 1803 Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. Element A 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other elements. + Dalton’s Atomic Theory 3. Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds. + Dalton’s Atomic Theory 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction. + J.J. Thomson 1897 (with Crookes & Millikan) discovery of the electron (e-) disproved Dalton’s theory; atoms DID have smaller parts after all Used a cathode ray tube to prove that there were charged particles (stream of (-) particles) within the atom + Thomson Model Plum pudding model aka chocolate chip cookie model Millikan found out that electrons were negatively charged and had a mass of 1/1840 of a hydrogen atom + Video Links to Experiments JJ Thomson’s Cathode Ray Tube How does it work? Rutherford’s Gold Foil Experiment What did he do? + Ernest Rutherford 1911 Used alpha particles to shoot at gold foil. Got unexpected results. Something was deflecting particles back to the source. Buried next to Sir Issac Newton and Lord Kelvin in Westminster Abbey. + Empty Space Nucleus Electrons Rutherford said, + “Atoms have a nucleus!” Dense & positively charged Contains most of the mass of the atom Contains the protons (positive charge; heavy) Electrons are around the outside of the nucleus flying around the empty space + Video Links to Experiments JJ Thomson’s Cathode Ray Tube How does it work? Rutherford’s Gold Foil Experiment What did he do? + James Chadwick Discovered Has the neutron in 1932 a neutral charge Found in the nucleus About ½ of the mass of the nucleus Wanted to know where the extra mass was coming from in an atom; shot particles @ beryllium Eventually led to experiments to bombard atoms with neutrons –> uranium bombs! + Niels Bohr - 1913 Created the Bohr model Electrons travel in definite orbits/ energy levels around the nucleus aka “Planetary Model” – orbit the nucleus like planets around the sun Electrons have fixed amounts of energy “quanta” Low energy closer to nucleus High energy further from nucleus + Bohr Model + Werner Heisenberg, 1927 It’s impossible to know both the location and the motion of an electron at the same time Heisenberg Uncertainty Principle + Quantum Mechanical Model (aka wave mechanical model) Erwin Schrodinger – 1926 Electrons Electrons DO NOT orbit the nucleus DO have quanta of energy that determine placement in an atom + Electron Cloud Area where there is a high probability that the electron will reside there 90% of the time + Schrodinger’s Cat + + + Subatomic Particles + Electron Cloud - electrons - o + + o - Nucleus - protons - neutrons + + p 0 n Found in the nucleus Found in the nucleus Mass = 1 (amu) Same mass as a proton Relative charge = +1 Mass = 1 amu Relative charge = 0 e Found in the electron cloud around the nucleus Mass 1836 times smaller than a proton Therefore, mass doesn’t really count! (0.0005 amu) Relative charge = -1 + Atomic Number Atomic Number Z = p+ 18.99 the number of protons in the nucleus ALL atoms of the SAME element have the SAME atomic number and SAME protons In a neutral atom, + p PROTONS IDENTIFY THE ELEMENT! = Magnesium = Z = 12 12 protons e + Mass Mass Number (nucleus!) number = p+ + n0 (electrons don’t have much mass!!!) Z = 82 LEAD, Pb Protons? 82 Electrons? 82 Mass 207 Neutrons? 125 #n0 = MN - # p+ = 207 – 82 = 125 neutrons + An element has an atomic number of 6 and a mass number of 14. What is the element? Z = 6 CARBON How many neutrons? MN = 14 #n = MN – #p+ = 14 – 6 = 8 neutrons + Group number (column) the second digit tells us the number of valence (outer) electrons in a Bohr atom Period number (row) the number of energy levels outside of the nucleus 17 2 Average atomic mass (not the mass #) 18.99 + Bohr model of the atom (protons & neutrons) Yep! Somebody lied when they told you 8! We’ll go into details in Unit 4. Hold your horses… + Identify this atom: (assuming it is neutral p+ = e-) NUCLEAR NOTATION 16 8 O HYPHEN NOTATION Oxygen - 16 + If we drew a Bohr model of sodium: How many protons? How many neutrons? How many energy levels? How many electrons? 23 Na + Scanning Electron Microscopes http://www.youtube.com/watch?v=egPQZw0QkVw