Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Particles, Nuclei, and Isotopes The Nuts and Bolts of Chemistry Atomic History: An Overview • • • • • • Early Greeks - Democritus vs Aristotle Dalton’s Atomic Theory Thomson - discovery of electrons Rutherford - discovery of nucleus Chadwick - discovery of neutron Bohr - planetary model of atom Atomic History: An Overview • • • • • • Early Greeks - Democritus vs. Aristotle Dalton’s Atomic Theory Thomson - discovery of electrons Rutherford - discovery of nucleus Chadwick - discovery of neutron Bohr - planetary model of atom Early Greeks • What is the nature of matter? -Infinitely divisible pieces of “stuff” -Earth, Air, Fire ,and Water • No experiments Early Greeks Democritus vs. Aristotle • Democritus • Aristotle • New idea • “atomos” - indivisible • Eventually, can’t divide matter any more • First “atomic theory” • Didn’t buy it… • All things are infinitely divisible Guess who won? (Aristotle) For 2000 years, scientists thought all matter was infinitely divisible… Atomic History: An Overview • • • • • • Early Greeks - Democritus vs Aristotle Dalton’s Atomic Theory Thomson - discovery of electrons Rutherford - discovery of nucleus Chadwick - discovery of neutron Bohr - planetary model of atom Dalton’s Atomic Theory John Dalton • 1807 • Idea of “atom” – Solid spheres that were indestructible – Unique to each element – Combine evenly – Reactions are rearrangements Dalton’s Atomic Theory • Atoms combine evenly in compounds – Small, whole number proportions – (e.g.) water - H20 (not H1O1/2 ) H H O H O H Atomic History: An Overview • • • • • Dalton’s Atomic Theory Thomson - discovery of electrons Rutherford - discovery of nucleus Chadwick - discovery of neutron Bohr - planetary model of atom Thomson’s Discovery J.J. Thomson 1897 • Studied electricity not atomic structure • His 1st observation was that a magnet could deflect the current and realized that it was made of particles • So to study current he pumped all the air out of a glass tube and applied voltage to two metal plates + (anode)/- (cathode) Thomson’s Discovery (cont…) J.J. Thomson 1897 • He then sent a ray of particles through the tube and saw that they came out of the cathode side and were attracted to the anode side and the tube glowed • This told him that the particles were negative… he called his discovery a Cathode Ray Tube – Sends a “ray” of - particles – Used in TVs and Computers Thomson’s Discovery • The beam was attracted to the positive plate. • So, cathode rays are negative • He realized that these negative particle must be ELECTRONS Thomson’s Discovery • Most books give Thomson credit for discovering the proton • He and Millikan found the mass of an electron to be much smaller than an atom • So, electrons are VERY VERY small • Protons must be large in comparison – Plum Pudding Model Plum Pudding Model Preface: “Plum Pudding” atomic model • atoms are solid • made of positively-charged material • with negative “bits” scattered throughout (like raisins in plum pudding) (or raisin bread) Atomic History: An Overview • • • • • Dalton’s Atomic Theory Thomson - discovery of electrons Rutherford - discovery of nucleus Chadwick - discovery of neutron Bohr - planetary model of atom Rutherford’s Discovery Ernest Rutherford Image courtesty of http://www.nobel.se/chemistry/laureates/1908/rutherford-bio.html Gold Foil Experiment To test the Plum Pudding Model (1907): • Shot alpha rays at thin gold foil – (about 2000 atoms thick) • EXPECTED to see the ray scatter as it hit all the solid positive atoms – Like spray from a nozzle Gold Foil Experiment Here is what they saw: Gold Foil Experiment In Detail: Click here to see an animation. Gold Foil Experiment RESULTS • Most of the particles were not deflected • Some were minimally deflected • VERY few (1 in 20,000) bounced back – “as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you.” Rutherford Gold Foil Experiment CONCLUSIONS • Plum pudding model wrong • A “nucleus” exists – It is tiny – It is densely-packed and positively-charged (this is the only way a strong positive particle could be deflected) • Empty spaces exist in atoms – LOTS of it!!!! Gold Foil Experiment How much empty space? • Use a billiard ball to represent a nucleus • The electrons occupy a volume one kilometer in ALL DIRECTIONS • Most of that space is EMPTY. Atomic History: An Overview • • • • • Dalton’s Atomic Theory Thomson - discovery of electrons Rutherford - discovery of nucleus Chadwick - discovery of neutron Bohr - planetary model of atom Chadwick’s Discovery (1932) Chadwick • PROBLEM • There was more mass in nucleus than explained by protons alone • Where did it come from? • NEUTRONS Atomic History: An Overview • • • • • Dalton’s Atomic Theory Thomson - discovery of electrons Rutherford - discovery of nucleus Chadwick - discovery of neutron Bohr - planetary model of atom Bohr’s Atomic Model • Nucleus has + charge • Electrons have charge • Why don’t electrons simply “fall into” the nucleus? Bohr Bohr’s Atomic Model • Bohr pictured atoms as little solar systems • Nucleus in center • Electrons “orbiting” in circles –We now know this isn’t correct –But it helps to explain many things about atoms What Theory Do We Currently Support? • Electron Cloud Model – Nucleus is composed of Protons and Neutrons – Electrons spin very quickly around the nucleus forming a “giant cloud” of negative energy – These electrons can move further away or closer to the nucleus at anytime – Their distance and space is infinite! HOMEWORK Notes 4.2 Protons, Neutrons, and Electrons Three Main Subatomic Particles • Protons – Located in nucleus – Positively charged (+1) – Mass = “1” mass unit (or 1 gram/mole) • Number of protons = atomic number (Z) Protons, Neutrons, and Electrons Three Main Subatomic Particles • Neutrons – Located in nucleus – no charge (0) – Mass = “1” mass unit (or 1 gram/mole) Protons, Neutrons, and Electrons Three Main Subatomic Particles • Electrons – Located outside nucleus – negative charge (-1) – So small we assume mass = 0 • Actual mass of 0.000 5 g/mol Protons, Neutrons, and Electrons Atomic number (Z) • shown in lower left • ALWAYS equals the number of protons • Equals the number of electrons in a neutral atom Isotope Notation C 6 Protons, Neutrons, and Electrons Mass Number (A) • shown in upper left • Is the sum: neutrons + protons • In this example, carbon has 6 protons and 7 neutrons Isotope Notation C 13 6 Protons, Neutrons, and Electrons We call this atom “carbon-13” Isotope Notation C 13 6 Protons, Neutrons, and Electrons • Atoms with the same number of protons can have different numbers of neutrons. • We call such atoms isotopes Protons, Neutrons, and Electrons • Atoms with the same number of protons can have different numbers of neutrons. • We call such atoms isotopes 12 13 14 C 6 carbon -12 C 6 carbon -13 C 6 carbon -14 Protons, Neutrons, and Electrons C C C 12 13 14 6 6 6 6 protons 6 electrons 6 neutrons 6 protons 6 electrons 7 neutrons 6 protons 6 electrons 8 neutrons All three kinds of carbon atoms have the same chemistry! Protons, Neutrons, and Electrons 1 1 H 1 proton 1 electron 0 neutrons 208 82 Pb +2 19 82 protons 80 electrons 126 neutrons 9 F 9 protons 9 electrons 10 neutrons Neutrons = A - Z Neutrons = A - Z Neutrons = A - Z 1-1=0 208 - 82 = 126 19 - 9 = 10 Protons, Neutrons, and Electrons 7 3 ? What element is this? How do you know? Protons, Neutrons, and Electrons 7 3 Li What element is this? Lithium How do you know? the atomic number is 3 look on the periodic table Protons, Neutrons, and Electrons 207 ? Pb 235 92 ? ? 19 K # of protons (Z) 82 92 19 # of neutrons 125 143 21 # of electrons 82 92 19 mass number (A) 207 235 40 lead-207 uranium-235 potassium-40 name Homework… Complete the Atomic Structure Worksheets ((((( Back AND Front )))))