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CHAPTER 3 THE STRUCTURE OF MATTER CHAPTER 3 LABORATORY CHEMISTRY 1 ATOMIC STRUCTURE 1. 2. 3. 4. EARLY MODELS OF THE ATOM DISCOVERING ATOMIC STRUCTURE MODERN ATOMIC THEORY CHANGES IN THE NUCLEUS CHAPTER 3 LABORATORY CHEMISTRY 2 EARLY MODELS OF THE ATOM DEMOCRITUS: (450 BC) – “ATOMOS” DEMOCRITUS THE SMALLEST PARTICLE OF AN ELEMENT THAT RETAINS THE CHEMICAL IDENTITY OF THAT ELEMENT. ARISTOTLE: – EARTH, AIR, FIRE, AND WATER CHAPTER 3 LABORATORY CHEMISTRY 3 EARLY MODELS OF THE ATOM LAVOISIER, ANTON: (LATE 1700’S) – LAW OF CONSERVATION OF MATTER (AND ENERGY) PROUST, JOSEPH: (1799) – LAW OF CONSTANT COMPOSITION DALTON, JOHN (1803) – SCHOOL TEACHER – ATOMIC THEORY OF MATTER CHAPTER 3 LABORATORY CHEMISTRY 4 EARLY MODELS OF THE ATOM DALTON’S ATOMIC THEORY – EACH ELMENT IS COMPOSED OF EXTREMELY SMALL PARTICLES CALLED ATOMS. – ALL ATOMS OF A GIVEN ELEMENT ARE IDENTICAL, BUT THEY DIFFER FROM THOSE OF ANY OTHER ELEMENT. – ATOMS ARE NEITHER CREATED NOR DESTROYED IN ANY CHEMICAL REACTION. – A GIVEN COMPOUND ALWAYS HAS THE SAME RELATIVE NUMBERS AND KINDS OF ATOMS. CHAPTER 3 LABORATORY CHEMISTRY 5 EARLY MODELS OF THE ATOM WHY IS THERE SUCH DIVERSITY IN NATURE IF THERE ARE ONLY ABOUT 100 DIFFERENT KINDS OF ATOMS ? CHAPTER 3 LABORATORY CHEMISTRY 6 DISCOVERING ATOMIC STRUCTURE FARADAY, MICHAEL (1839) – SUGGESTED THAT THE STRUCTURE OF ATOMS WAS RELATED TO ELECTRICITY. FRANKLIN, BENJAMIN (MID-1700’S) – STATIC ELECTRICITY – BATTERIES – “POSITIVE AND NEGATIVE CHARGES” CHAPTER 3 LABORATORY CHEMISTRY 7 DISCOVERING ATOMIC STRUCTURE CATHODE RAY TUBE – INVENTED IN THE MID-1800’S ELECTRON BEAM ANODE + CATHODE CHAPTER 3 LABORATORY CHEMISTRY 8 DISCOVERING ATOMIC STRUCTURE – THOMSON, J.J. (1896) CHAPTER 3 DISCOVERED AND NAMED ELECTRONS DETERMINED THE CHARGE (1.76 X 108 COULOMBS/GRAM) “PLUM-PUDDING” MODEL OF THE ATOM LABORATORY CHEMISTRY 9 DISCOVERING ATOMIC STRUCTURE – RUTHERFORD, ERNEST (EARLY 1900’S) ALPHA(2+) AND BETA(1-) RADIATION (GAMMA RADIATION WAS DISCOVERED LATER) – MADE OF PARTICLES CHAPTER 3 LABORATORY CHEMISTRY 10 RUTHERFORD’S GOLD FOIL EXPERIMENT GOLD FOIL CHAPTER 3 LABORATORY CHEMISTRY 11 Niels Bohr ! DISCOVERING Hi..I’m ATOMIC And I love Physics ! STRUCTURE Well…I’m Ernie Rutherford ! And I love a good Cigar! THE NUCLEAR ATOM – ALPHA SCATTERING EXPERIMENT (GOLD FOIL EXPERIMENT) – RUTHERFORD NAMES THE NUCLEUS AND DETERMINES ITS CHARGE – THE RUTHERFORD/BOHR MODEL OF THE ATOM CHAPTER 3 LABORATORY CHEMISTRY 12 MODERN ATOMIC THEORY THE STRUCTURE OF THE ATOM – NUCLEUS PROTONS NEUTRONS – ELECTRONS – RUTHERFORD’S VISUALIZATION (MINATURE SOLAR SYSTEM) – UNCERTAINTY (ELECTRON CLOUD) CHAPTER 3 LABORATORY CHEMISTRY 13 “PLUMBPUDDING” MODEL “SOLAR SYSTEM” MODEL CHAPTER 3 LABORATORY CHEMISTRY 14 DISCOVERING ATOMIC STRUCTURE PARTICLE LOCATION CHARGE MASS (GRAMS) MASS (AMU) PROTON INSIDE NUCLEUS +1.602 X 10-19 1.673 X 10-24 1.0073 = 1 NEUTRON INSIDE NUCLEUS 0 1.675 X 10-24 1.0087 = 1 ELECTRON OUTSIDE NUCLEUS -1.602 X 10-19 9.109 10-29-28 9.109 XX 10 0.0006 = 0 1.63 X 10-24 NOTE THAT EVEN THOUGH THE MASS OF AN ELECTRON IS FAR LESS THAN A PROTON….THE CHARGES ARE OF THE SAME MAGNITUDE BUT OPPOSITE CHAPTER 3 LABORATORY CHEMISTRY 15 DISCOVERING ATOMIC STRUCTURE ATOMIC NUMBERS – MOSELEY, HENRY (1887-1915) CHAPTER 3 STUDENT OF RUTHERFORD DISCOVERED THE PROTON (UNIQUE POSITIVE CHARGE OF THE NUCLEUS) ATOMIC NUMBER = NUMBER OF PROTONS IN THE NUCLEUS AND ALSO = THE NUMBER OF ELECTRONS AROUND THE NUCLEUS LABORATORY CHEMISTRY 16 DISCOVERING ATOMIC STRUCTURE PERIODIC TABLE ATOMIC NUMBER ATOMIC MASS CHAPTER 3 N 14.0067 7 NITROGEN LABORATORY CHEMISTRY Atomic Symbol Element Name 17 DISCOVERING ATOMIC STRUCTURE WRITING THE ELEMENTS TO CALCULATE PROTONS, NEUTRONS, AND ELECTRONS – TO CALCULATE THE NUMBER OF NEUTRONS, SUBTRACT THE NUMBER OF PROTONS FROM THE ATOMIC MASS – THE NUMBER OF ELECTRONS = THE NUMBER OF PROTONS (ATOMIC NUMBER) IN A NEUTRAL ATOM CHAPTER 3 LABORATORY CHEMISTRY 18 DISCOVERING ATOMIC STRUCTURE ATOMIC MASS “” IN AMU ATOMIC NUMBER “Z” NUMBER NUMBER OF NEUTRONS CHAPTER 3 23 11 12 Na LABORATORY CHEMISTRY THIS IS ALSO THE NUMBER OF ELECTRONS IN A GROUND STATE ATOM!!!!! 19 DISCOVERING ATOMIC STRUCTURE IONS – WHEN AN ATOM GAINS OR LOSES AN ELECTRON IT ACQUIRES AN ELECTRICAL CHARGE – PLACE THE APPROPRIATE CHARGE SIGN AND NUMBER AT THE UPPER RIGHT OF THE ELEMENT SYMBOL CHARGE OF AN ION = NUMBER OF PROTONS-NUMBER OF ELECTRONS N3+ O2- Fe2+ Cl2- Ca2+ CHAPTER 3 LABORATORY CHEMISTRY 20 PRACTICE LOSES 3 ELECTRONS 14 7 N 14 7 GROUND STATE ATOM NEUTRAL (NO CHARGE) (+7) + (-7) = 0 THE NUMBER OF PROTONS DO NOT CHANGE N +3 AN ION A CHARGED ATOM (+7)+( -4) = 3 + CHARGE ELECTRONS PROTONS PROTONS ELECTRONS CHARGE CHAPTER 3 LABORATORY CHEMISTRY 21 DISCOVERING ATOMIC STRUCTURE ISOTOPES – ATOMS THAT HAVE THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS (OVERWEIGHT OR UNDERWEIGHT ATOMS) – NAMED BY THE ISOTOPES MASS NUMBER (PROTONS + NEUTRONS) CHAPTER 3 LABORATORY CHEMISTRY 22 DISCOVERING ATOMIC STRUCTURE 12 6 C 14 6 GROUND STATE CARBON RADIOACTIVE CARBON CARBON-12 CHAPTER 3 C CARBON-14 LABORATORY CHEMISTRY 23 DISCOVERING ATOMIC STRUCTURE THE MASS OF AN ATOM – ATOMIC MASS UNITS (AMU) – AVERAGE MASS OF AN ELEMENT’S ATOMS IS CALLED THE ATOMIC MASS. CHAPTER 3 LABORATORY CHEMISTRY 24 CHANGES IN THE NUCLEUS NUCLEAR REACTIONS CHANGE THE COMPOSITION OF AN ATOM’S NUCLEUS. NUCLEAR STABILITY – STABLE NUCLEUS (NOT RADIOACTIVE) RADIOACTIVE DECAY – RADIATION (ALPHA, BETA, AND GAMMA) CHAPTER 3 LABORATORY CHEMISTRY 25 CHANGES IN THE NUCLEUS TYPES OF RADIATION NAME IDENTITY CHARGE Alpha () Helium-4 nuclei 2+ Beta () electrons 1- Gamma () High energy non-particle radiation none CHAPTER 3 LABORATORY CHEMISTRY PENETRATING ABILITY Low, stopped by paper Medium, stopped by heavy clothing High, stopped by lead 26 ALPHA-BETA-GAMMA SCATTERING CHAPTER 3 LABORATORY CHEMISTRY 27 CHANGES IN THE NUCLEUS Alpha decay 226 88 CHAPTER 3 Ra Rn 222 86 LABORATORY CHEMISTRY 4 2 28 CHANGES IN THE NUCLEUS Hello, my name is Lise Meitner. I was born in Austria, and fled to Denmark when the Nazis took power in the early 1930’s. I was the physicist who interpreted the work of Otto Hahn and Fritz Straussman in 1932. I worked with my nephew, Otto Frisch, and concluded that neutrons actually cleaved the nucleus of an atom of uranium into two or more fragments. This was never suspected. I also coined the phrase “NUCLEAR FISSION”. After World War II I moved to the U.S. CHAPTER 3 LABORATORY CHEMISTRY 29 CHANGES IN THE NUCLEUS Beta decay I 131 53 CHAPTER 3 131 54 Xe LABORATORY CHEMISTRY 0 1 30 CHANGES IN THE NUCLEUS Gamma decay U 235 92 CHAPTER 3 U 235 92 LABORATORY CHEMISTRY 0 0 31 CHANGES IN THE NUCLEUS WHAT CHANGES ACCOMPANY A NUCLEAR REACTION? DEFINE RADIOACTIVITY. IS ALL RADIOACTIVITY COMPOSED OF PARTICLES ? DESCRIBE THE FORCE THAT HOLDS THE NUCLEUS TOGETHER. CHAPTER 3 LABORATORY CHEMISTRY 32