Quiz: October 19, 2004 How many significant figures are in the number 101.00? What is the density of an object with a mass of 1.0g and a volume of 2.00 ml? In the experiment: What is the effect of caffeine on the pulse of people 20 and older? Identify the independent and dependent variables. What question are you asking for your science fair project. Underline the independent variable, circle the dependent variable. Who is responsible for the development of the “modern” atomic theory. 5 sig. digs. 1.0g/2.0 ml = 0.50 g/mL Amount of caffeine = independent variable; pulse rate = dependent variable What is the effect of ___ on O? Charles Dalton

Chapter 4 Atomic Structure www.ec.njit.edu.atoms.files pictures. Democritus http://www.utm.edu/research/iep/d/democrit.htm http://mot.cprost.sfu.ca/~rhlogan/democ.html http://www.phys.virginia.edu/classes/252/atoms.html Dalton http://kcs.korea.ac.kr/education/fame/dalton.html http://c.chem.ualberta.ca/~plambeck/che/p101/p01021.htm Thomson http://www.fc.peachnet.edu/FLOYD/academics/chemistry/Disc-of-Electron-Intro.html http://www.aip.org/history/electron/ http://hyperion.advanced.org/10380/index.shtml http://iop.org/Physics/Electron/ Rutherford http://www.pbs.org/wgbh/aso/databank/entries/dp13at.html http://www.windows.umich.edu/people/modern_era/rutherford.html http://www.iop.org/Physics/Electron/Exhibition/section3/1911a.html Bohr http://www.wpi.edu/~kromano/ph1121.html http://www2.lucidcafe.com/lucidcafe/library/95oct/nbohr.html Modern / Wave Atomic Theory http://www.svidaho.net/atom/pg2.html

Dalton’s Atomic Theory Elements are made of tiny particles called atoms. All atoms of a given element are identical. All atoms of a given element are different from the atoms of other elements. Atoms can combine with each (in small whole number ratios) other to form different compounds. (ex: NO, NO2, N2O) Atoms are indivisible. http://dl.clackamas.cc.or.us/ch104-04/dalton's.htm http://encarta.msn.com/encyclopedia_761567432_5/Atom.html Atoms can be divided. Electrons are transferred during chemical reactions, and nuclear reactions are possible, though rare. Atom = indivisible sphere

James Chadwick and Walter Bothe both discovered the proton. In 1932 Chadwick observed that beryllium, Be, when hit with alpha particles, released an unknown radiation that in turn ejected protons from the nuclei of various substances. Chadwick interpreted this radiation as being composed of particles of mass approximately equal to that of the proton, but without electrical charge--neutrons. http://www.britannica.com/nobel/micro/114_22.html Atom = sphere containing positive, negative, and neutral charges + + + X Be - Li X-1

Summary Democritus: Atom Aristotle: Continuous Matter Proust: the Law of Definite Composition Lavosier: the Law of Conservation of Matter Dalton: “Modern” Atomic Theory JJ Thompson: Discovery of Electrons Millikin: Charge/Mass ratio of electrons Moseley: Discovery of Protons/Atomic Number Chadwick and Bothe: Discovery of Neutrons

Rutherford’s Team: Neils Bohr, Hans Geiger, Ernest Marsden. Gold Foil Experiment. most of the alpha particles went straight through, some were deflected by a “large” mass. The PROTON was discovered. + Atom = sphere containing positive, negative charges, and some number of neutral particles, depending upon the isotope. The positive charges were located in the nucleus.

The Nuclear Atom Gold Foil Experiment. + most particles go straight through.

The Nuclear Atom Gold Foil Experiment. + most particles go straight through. Some are deflected by the nucleus

Summary Democritus: Atom Aristotle: Continuous Matter Proust: the Law of Definite Composition Lavosier: the Law of Conservation of Matter Dalton: “Modern” Atomic Theory JJ Thompson: Discovery of Electrons Millikin: Charge/Mass ratio of electrons Moseley: Discovery of Protons/Atomic Number Chadwick and Bothe: Discovery of Neutrons Rutherford: The Nuclear Atom

Henri Becquerel Found that matter containing uranium exposed sealed photographic film. +

Isotopes: J.J. Thomson observed two kinds of neon atoms. neon-20 and neon-21 Both neons are chemically identical, but their masses differ. Atom = sphere containing positive, negative charges, and neutral particles.

Isotopes neutrons! What causes the extra mass? Isotope Atomic number Number of protons Number of electrons Mass number H-1 1 H-2 2 H-3 3 P-31 15 31 + 0 = 1 + 1 = 2 + 2 = 3 + 16 = 31

Time-Line of Discovery http://www.chemheritage.org/explore/matter-time.html Other web sites http://www.slcc.edu/schools/hum_sci/physics/whatis/biography/dalton.html http://www.chemheritage.org/EducationalServices/chemach/ppt/jd.html http://antoine.frostburg.edu/chem/senese/101/atoms/dalton.shtml http://www.fact-index.com/l/la/law_of_definite_proportions.html