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MATTER UNIT STRUCTURE OF AN ATOM • HTTPS://WWW.YOUTUBE.COM/WATCH?V=THNDXFDKZZS WHAT IS AN ATOM? Atom: the smallest unit of matter that retains the identity of the substance THE EVOLUTION OF ATOMIC STRUCTURE 460 B.C. – DEMOCRITUS • DEMOCRITUS BELIEVED THAT ALL MATTER WAS COMPOSED OF ATOMS THAT COULD BE DIVIDED NO FURTHER. 1800 – JOHN DALTON DALTON'S ATOMIC THEORY: MATTER IS COMPOSED OF SMALL PARTICLES CALLED ATOMS. ALL ATOMS OF AN ELEMENT ARE IDENTICAL, BUT ARE DIFFERENT FROM THOSE OF ANY OTHER ELEMENT. DURING CHEMICAL REACTIONS, ATOMS ARE NEITHER CREATED NOR DESTROYED, BUT ARE SIMPLY REARRANGED. ATOMS ALWAYS COMBINE IN WHOLE NUMBER MULTIPLES OF EACH OTHER. FOR EXAMPLE, 1:1, 1:2, 2:3 OR 1:3. 1897- J.J. THOMSON THOMSON’S RAISIN IN THE PUDDING MODEL OF THE ATOM • HE DISCOVERED THE ELECTRON AND PROPOSED A MODEL FOR THE STRUCTURE OF THE ATOM. Positive Sphere Negative Charges Discovery of the Electron 1910 – ERNST RUTHERFORD Rutherford’s Gold Foil Experiment Rutherford’s Findings “Like howitzer shells bouncing off of tissue paper!” Conclusions: The nucleus is small The nucleus is dense The nucleus is positively charged 1912 – NIELS BOHR Bohr’s Finding: Quantized energy levels Electron moves in a circular orbit Electron jumps between levels by absorbing or emitting photon of a particular wavelength HOW EXACTLY ARE THE PARTICLES ARRANGED? Bohr Model of the atom: All of the protons and the neutrons The 3rd ring can hold up to 8 eThe 4th ring and any after can hold up to 18 e- The 1st ring can hold up to 2 eThe 2nd ring can hold up to 8 e- WHAT DOES CARBON LOOK LIKE? Mass # = 12 atomic # = 6 6 p and 6 n live in the nucleus p+ = 6 no = 6 e- = 6 JAMES CHADWICK 1932 Discovered the Neutron. QUANTUM MECHANICAL MODEL • ELECTRONS ARE LOCATED IN SPECIFIC ENERGY LEVELS. • THERE IS NO EXACT PATH AROUND THE NUCLEUS. • THE MODEL ESTIMATES THE PROBABILITY OF AN ELECTRONS POSITION THE ELECTRON CLOUD THE ELECTRON CLOUD CONTAINS THE ELECTRONS. MODERN ATOMIC THEORY • ELEMENT HAVE A CHARACTERISTIC AVERAGE MASS WHICH IS UNIQUE TO THAT ELEMENT. • ATOMS CANNOT BE SUBDIVIDED, CREATED, OR DESTROYED IN ORDINARY CHEMICAL REACTIONS. HOWEVER, THESE CHANGES CAN OCCUR IN NUCLEAR REACTIONS! • ALL MATTER IS COMPOSED OF ATOMS • ATOMS OF ANY ONE ELEMENT DIFFER IN PROPERTIES FROM ATOMS OF ANOTHER ELEMENT Atoms ATOMIC STRUCTURE are composed of 2 regions: Nucleus: the center of the atom that contains the mass of the atom Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Electron Cloud Nucleus ATOMIC STRUCTURE The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged subatomic particles Neutrons: neutrally charged subatomic particles The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic particle with a negative charge and relatively no mass Atomic Particles Particle Charge Electron -1 Mass # 0 Proton +1 0 Neutron Location symbol Electron cloud e- 1 Nucleus p+ 1 Nucleus n0 HOW DO THESE PARTICLES INTERACT? Protons and neutrons are in the tiny positively charged nucleus accounting for most of the mass of the atom The negatively charged electrons are small and have a relatively small mass but occupy the larger volume of space outside the nucleus HOW DO THE SUBATOMIC PARTICLES BALANCE EACH OTHER? In an atom: The # of protons = The # of electrons If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral The neutrons have no charge they do not have to equal the number of protons or electrons THE NUMBER OF PROTONS IDENTIFIES THE ATOM. • AN ATOM WITH 6 PROTONS = CARBON • AN ATOM WITH 8 PROTONS = OXYGEN • AN ATOM WITH 20 PROTONS = CALCIUM ATOMIC STRUCTURE He 2 Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom # of electrons = # of protons # of neutrons = Atomic mass – # of protons DETERMINE THE NUMBER OF SUBATOMIC PARTICLES IN THE FOLLOWING: Cl has a mass # of 35 and an atomic # of 17 p+ = 17, no = 18, e- = 17 K has a mass # of 39 and an atomic # of 19 P+ = 19, no = 20 e- = 19