BASIC ATOMIC THEORY UNIT 2 CHAPTER 3 ELECTRONS

BASIC ATOMIC THEORY UNIT 2 (CHAPTER 3) ELECTRONS, PROTONS, & NEUTRONS, RELATIVE ATOMIC MASS (& ISOTOPES), THE MOLE AND MOLAR MASS

WKRP IN CINCINNATI ATOM LESSON: HTTPS: //YOUTU. BE/WJCMU 9 IJY 1 O (2: 13 -6: 02)

Particle Symbol Electron e-, 0 -1 e Relative Mass electric numbe charge r Relative mass (amu) Actual mass (kg) -1 0 p+, 11 H +1 1 0. 000548 9. 109 x 10 -31 6 1. 007276 1. 673 x 10 -27 Neutron n 0, 10 n 0 1 1. 008665 1. 675 x 10 -27 Proton *1 amu (atomic mass unit) = 1. 660540 x 10 -27 kg Similar chart on page 76 in your

�ATOMIC NUMBER (Z) = THE NUMBER OF PROTONS IN THE NUCLEUS OF AN ATOM OF THAT ELEMENT. �Z IS FROM THE GERMAN ZAHL OR “NUMBER. ” �MASS NUMBER (I. E. ATOMIC MASS) [A] = TOTAL NUMBER OF PROTONS AND NEUTRONS IN THE NUCLEUS OF AN ISOTOPE. �A FROM GERMAN ATOMGEWICHTE OR “ATOMIC

WHAT MAKES THE ATOMIC MASS DIFFERENT? � ISOTOPES = ATOMS OF THE SAME ELEMENT THAT HAVE DIFFERENT MASSES (I. E. DIFFERENT NUMBERS OF NEUTRONS). THEY MAY BE NATURALLY OCCURRING OR MAN-MADE IN A LABORATORY.

ION: AN ATOM OR GROUP OF BONDED ATOMS THAT HAS A POSITIVE OR NEGATIVE CHARGE AS A RESULT OF HAVING EITHER MORE OR LESS ELECTRONS THAN THE NEUTRAL ATOM FROM WHICH IT ORIGINATED. ANY PROCESS THAT RESULTS IN THE FORMATION OF AN ION IS CALLED IONIZATION. OXIDATION NUMBER/STATE/VALENCE: A NUMBER ASSIGNED TO AN ATOM IN A MOLECULAR COMPOUND OR MOLECULAR ION THAT INDICATES THE GENERAL DISTRIBUTION OF ELECTRONS AMONG THE BONDED

ATOMIC MASS UNIT, OR 1 AMU, IS EXACTLY 1/12 THE MASS OF A CARBON-12 ATOM. THE ATOMIC MASS OF ANY NUCLIDE IS DETERMINED BY COMPARING IT WITH THE MASS OF THE CARBON-12 ATOM. AVERAGE ATOMIC MASS IS THE WEIGHTED AVERAGE OF THE ATOMIC MASSES OF THE NATURALLY OCCURRING ISOTOPES OF AN ELEMENT. THIS IS WHAT WE SEE ON THE PERIODIC TABLE.

�LAW OF CONSERVATION OF MASS: MASS IS NEITHER CREATED NOR DESTROYED DURING ORDINARY CHEMICAL REACTIONS OR PHYSICAL CHANGES. �LAW OF DEFINITE PROPORTIONS: A CHEMICAL COMPOUND CONTAINS THE SAME ELEMENTS IN EXACTLY THE SAME PROPORTIONS BY MASS REGARDLESS OF THE SIZE OF THE SAMPLE OR SOURCE OF THE COMPOUND. �LAW OF MULTIPLE PROPORTIONS: IF TWO OR MORE DIFFERENT COMPOUNDS ARE COMPOSED OF THE SAME TWO ELEMENTS, THEN THE RATIO OF THE MASSES OF THE SECOND ELEMENT

• MY. HRW. COM VIDEO CLIPS

CALCULATING AVERAGE ATOMIC MASS MULTIPLYING THE ATOMIC MASS OF EACH ISOTOPE BY ITS RELATIVE ABUNDANCE (EXPRESSED IN DECIMAL FORM) AND ADDING THE RESULTS: EXAMPLE: COPPER, Cu (0. 6917 X 62. 929599 AMU) + (0. 3083 X 64. 927793 AMU) = 63. 55 AMU RELATIVE ABUNDANCE IS DETERMINED USING A MASS SPECTROMETER

ACCELERATOR MASS SPECTROMETER AT LAWRENCE LIVERMORE NATIONAL LABORATORY

UEIP. ORG/MASS-SPECTROMETER-ISOTOPEANALYSIS-U. . .

LET’S TAKE A TRIP THROUGH TIME!

DEMOCRITUS 460 – 370 B. C. • THERE ARE VARIOUS BASIC ELEMENTS FROM WHICH ALL MATTER IS MADE • EVERYTHING IS COMPOSED OF SMALL ATOMS MOVING IN A VOID • SOME ATOMS ARE ROUND, POINTY, OILY, HAVE HOOKS, ETC. TO ACCOUNT FOR THEIR PROPERTIES • IDEAS REJECTED BY LEADING PHILOSOPHERS BECAUSE VOID

JOHN DALTON 1766 -1844 • INTRODUCED HIS IDEAS IN 1808 • EACH ELEMENT IS COMPOSED OF EXTREMELY SMALL PARTICLES CALLED ATOMS • ALL THE 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

Which parts of Dalton’s theory are no longer “true” today? Elements can have atoms with different masses (isotopes) Atoms are divisible into even smaller particles (like what? )

• DISCOVERED ELECTRON 1897 – CATHODE RAY EXPERIMENT • PLUM PUDDING MODEL 1904 • ELECTRONS IN A SOUP OF POSITIVE CHARGES J. J. THOMSON 1856 -1940

DISCOVERY OF THE ELECTRON Cathode ray tube 1. AN OBJECT PLACED BETWEEN THE CATHODE AND THE OPPOSITE END OF THE TUBE CAST A SHADOW ON THE GLASS. 2. A PADDLE WHEEL PLACED ON RAILS BETWEEN THE ELECTRODES ROLLED ALONG THE RAILS FROM THE CATHODE TOWARD THE ANODE. 3. CATHODE RAYS WERE DEFLECTED BY A MAGNETIC FIELD IN THE SAME MANNER AS A WIRE CARRYING ELECTRIC CURRENT, WHICH WAS KNOWN TO HAVE NEGATIVE CHARGE. 4. THE RAYS WERE DEFLECTED AWAY FROM A NEGATIVELY CHARGED

He concluded that cathode rays are composed of identical negatively charged particles that were later named electrons. THESE OBSERVATIONS LED TO THE HYPOTHESIS THAT THE PARTICLES THAT COMPOSE CATHODE RAYS ARE NEGATIVELY CHARGED. THIS WAS SUPPORTED BY EXPERIMENTS UNDERTAKEN BY J. J. THOMPSON IN 1897. IN ONE EXPERIMENT HE FOUND THAT THE RATIO OF THE CHARGE OF CATHODE-RAY PARTICLES TO THEIR MASS WAS

MILLIKAN’S OIL DROP EXPERIMENT (1909) HE DETERMINED THE MASS OF AN ELECTRON. Mass of an electron: 9. 109 x 10 -31 kg

DISCOVERY OF THE ATOMIC NUCLEUS ERNEST RUTHERFORD, HANS GEIGER AND ERNEST MARSDEN (1911) Ernest Rutherford (1871 -1937) THEY BOMBARDED A VERY THIN PIECE OF GOLD FOIL WITH ALPHA PARTICLES (ABOUT FOUR TIMES THE MASS OF A HYDROGEN ATOM). THEY FOUND THAT THE MAJORITY OF THE PARTICLES WENT STRAIGHT THROUGH THE FOIL

ALPHA PARTICLE EXPERIMENT

THEREFORE, EACH ATOM IN THE GOLD FOIL HAD A VERY SMALL, DENSE, POSITIVELY CHARGED NUCLEUS SURROUNDED BY ELECTRONS.

JAMES CHADWICK 1891 -1974 • WORKED WITH RUTHERFORD • INTERPRETED WORK OF THE CURIES • DISCOVERED NEUTRON 1932 • NOBEL PRIZE IN PHYSICS 1935

DISCOVERY OF THE NEUTRON LIBRARY. THINKQUEST. ORG/27954/NEUTRON. HT ML IN 1932, JAMES CHADWICK BOMBARDED BERYLLIUM (Be) WITH ALPHA PARTICLES. HE ALLOWED THE RADIATION EMITTED BY It was found that protons were shot out from the paraffin wax. People began to look for what was in the "beryllium radiations".

SOME PEOPLE SUGGESTED THAT THE RADIATIONS MAY BE GAMMA RADIATION. HOWEVER, CHADWICK FOUND THAT THE RADIATION COULD NOT BE GAMMA RADIATION SINCE ENERGY AND MOMENTUM WERE NOT CONSERVED IN ITS PRODUCTION. HE SHOWED THAT ALL THE OBSERVATIONS COULD BE EXPLAINED IF THE RADIATION CONSISTED OF NEUTRAL PARTICLES OF MASS APPROXIMATELY EQUAL TO THAT OF PROTON. THIS NEUTRAL PARTICLE WAS NAMED NEUTRON. EQUATION OF THE NUCLEAR REACTION

THIS NEW TOOL IN ATOMIC DISINTEGRATION DID NOT HAVE TO OVERCOME ANY ELECTRIC BARRIER AND WAS CAPABLE OF PENETRATING AND SPLITTING THE NUCLEUS OF EVEN THE HEAVIEST ELEMENTS. CHADWICK THUS PREPARED THE WAY TOWARDS THE FISSION OF URANIUM 235 AND TOWARDS THE CREATION OF THE ATOMIC BOMB. FOR THIS DISCOVERY HE WAS AWARDED THE HUGHES MEDAL OF THE ROYAL SOCIETY IN 1932, AND SUBSEQUENTLY THE NOBEL PRIZE FOR PHYSICS IN 1935.

• PLANETARY MODEL 1913 • NUCLEUS SURROUNDED BY ORBITING ELECTRONS AT DIFFERENT ENERGY LEVELS • ELECTRONS HAVE DEFINITE ORBITS • UTILIZED PLANCK’S QUANTUM ENERGY THEORY • WORKED ON THE NIELS BOHR 1885 -1962

DISCOVERY OF THE NEUTRON LED TO THE BEGINNING OF CURRENT THEORIES OF NUCLEAR STRUCTURE. IMMEDIATELY, THE NEUTRON-PROTON MODEL ( THE RUTHERFORD-BOHR MODEL) OF THE NUCLEUS WAS ADOPTED: • THE NUCLEUS IS MADE UP OF PROTONS AND NEUTRONS. THESE ARE BOUND TOGETHER BY A STRONG NUCLEAR FORCE. • ELECTRONS AND PROTONS CARRY EQUAL BUT OPPOSITE CHARGES. IN

BOHR’ S MODE L

USUALLY LIKE CHARGES REPEL, BUT PROTONS AND NEUTRONS CAN BE VERY CLOSE TOGETHER. THESE SHORT-RANGE PROTON NEUTRON, PROTON, AND NEUTRON FORCES HOLD THE NUCLEAR PARTICLES TOGETHER AND ARE CALLED NUCLEAR FORCES

ERNST SCHRÖDINGER 18871961 Werner Heisenberg 19011976 • QUANTUM MECHANICAL MODEL 1926 • ELECTRONS ARE IN PROBABILITY ZONES CALLED “ORBITALS”, NOT ORBITS AND THE LOCATION CANNOT BE PINPOINTED • ELECTRONS ARE PARTICLES AND WAVES AT THE SAME TIME • DEVELOPED QUANTUM NUMBERS

THE MOLE A MOLE IS THE SI BASE UNIT USED TO MEASURE THE AMOUNT OF A SUBSTANCE WHOSE NUMBER OF PARTICLES IS THE SAME AS THE NUMBER OF ATOMS OF CARBON IN EXACTLY 12 G OF CARBON -12. IT IS EQUAL TO 6. 02 X 1023. SIMPLY REPRESENTS A NUMBER. JUST AS THE TERM DOZEN REFERS TO THE NUMBER TWELVE, THE MOLE REPRESENTS THE NUMBER 6. 02 X 1023

THE HISTORY OF THE MOLE AMADEO AVOGADRO (1811) PROPOSED THAT EQUAL VOLUMES OF DIFFERENT GASES AT THE SAME TEMPERATURE CONTAIN EQUAL NUMBERS OF MOLECULES.

STANISLAO CANNIZZARO ABOUT FIFTY YEARS LATER, STANISLAO CANNIZZARO USED AVOGADRO'S HYPOTHESIS TO DEVELOP A SET OF ATOMIC WEIGHTS FOR THE KNOWN ELEMENTS BY COMPARING THE MASSES OF EQUAL VOLUMES OF GAS.

JOHANN JOSEF LOSCHMIDT (AUSTRIAN HIGH SCHOOL TEACHER) 1865, CALCULATED THE SIZE OF A MOLECULE OF AIR, AND THUS DEVELOPED AN ESTIMATE FOR THE NUMBER OF MOLECULES IN A GIVEN VOLUME OF

MOLAR MASS – THE MASS OF ONE MOLE OF A PURE SUBSTANCE ONE MOLE OF ANY SUBSTANCE WILL CONTAIN ONE MOLE OF PARTICLES. 23 6. 02 X 10 • ELEMENTS = ATOMS • COMPOUNDS = MOLECULES

CALCULATING MOLAR MASS 1. MULTIPLY ATOMIC MASS OF EACH ELEMENT BY NUMBER OF ATOMS OF THAT ELEMENT IN THE FORMULA (SHOWN BY THE SUBSCRIPT) 2. FIND THE SUM OF ALL THE ATOMIC MASSES --THIS IS FORMULA MASS (UNIT IS A. M. U. ) 3. EXPRESS FORMULA MASS IN GRAMS (UNIT IS G/MOL). THIS IS THE MOLAR MASS.