Updated August 2006Created by C. Ippolito August 2006 Atomic Structure Objectives: 1.trace the development of models of the atom 2.show that atomic theory is consistent with experimental observations 3.describe the properties of atoms and subatomic particles 4.explain the relationship between emission spectra and atomic structure 5.use the concept of atomic mass 6.explain how the atomic number identifies an atom 7.explain the significance of isotopes and their relationship to atomic mass

Updated August 2006Created by C. Ippolito August 2006 Early Atomic Structure Democritus –A–A–A–Atomic Theory of Matter –a–all matter could be divided into tiny indivisible particles called a aa atoms –d–different types of atoms existed for each different type of material –n–not based on experimental evidence Aristotle –C–C–C–Continuous Theory of Matter –a–all matter was continuous and composed of one substance called hyle.

Updated August 2006Created by C. Ippolito August 2006 Law of Conservation of Mass Antoine Lavoisier –F–F–F–Father of Modern Chemistry quantitatively measured mass of reactants and compared it with mass of products found mass of overall system remained constant –L–L–L–Law of Conservation of Mass matter can be changed but cannot be created nor destroyed

Updated August 2006Created by C. Ippolito August 2006 Law of Definite Proportions Joseph Proust –r–regardless of where a substance came from or how large the sample –s–specific substances always contained elements in the same ratio by mass Law of Definite Proportions –a–all specific substances always contain elements in the same ratio by mass

Updated August 2006Created by C. Ippolito August 2006 Law of Multiple Proportions the ratio of the masses of one element that combines with another element can be expressed in whole numbers J L Gay- Lussac –o–observed reactions of gases at constant temperature and pressure –G–G–G–Gay-Lussac’s Gas Law under constant temperature and pressure the volume of gases reacting and the volume of gaseous products were related in a ratio of small whole numbers

Updated August 2006Created by C. Ippolito August 2006 Dalton’s Atomic Theory John Dalton –p–postulates to explain Lavoisier’s and Proust’s findings 1.Matter made of small particles (atoms) 2.Atoms are indestructible. Cannot be created or destroyed in chemical or physical changes. 3.Atoms of same element are identical, have the same mass. 4.Atoms of different elements are different, have different mass 5.Compounds form by combining atoms of different elements

Updated August 2006Created by C. Ippolito August 2006 Parts of the Atom in the late 1800’s experiments show that atoms are made of smaller particles –E–E–E–Elementary or S SS Subatomic Particles proton – positive charge, mass = 1 amu, in nucleus electron – negative charge, mass = 1/1837 amu, outside nucleus neutron – neutral charge, mass = 1 amu, in nucleus

Updated August 2006Created by C. Ippolito August 2006 Quantum Theory Max Planck –light can exist as “particles” quantum –discrete bundle of energy Neils Bohr –proposed that this was the energy gained or lost when electrons changed energy levels

Updated August 2006Created by C. Ippolito August 2006 Elements and Isotopes Isotope –Atoms of same element same atomic number (electrons & protons) –Have different atomic mass different number of neutrons

Updated August 2006Created by C. Ippolito August 2006 Electron Behavior Louis DeBroglie –If light can behave as particles then particles can behave as light Edwin Schrodinger sublevelsorbitals –Energy levels broken into sublevels or orbitals Werner Heisenberg –Uncertainty principle One cannot know both the energy and position of the electron at the same time –Particle – know location not energy –Wave – know energy not location

Updated August 2006Created by C. Ippolito August 2006 Crooke’s Tube William Crookes –s–studies matter in vacuum tubes with metal plates Cathode Plate –a–accumulated negative charge Anode Plate –a–accumulated positive charge –n–notices green glow in shape of anode moves from cathode to anode –C–C–C–Cathode Rays

Updated August 2006Created by C. Ippolito August 2006 Electron J J Thompson –c–cathode rays made of negative particles electrons –o–one unit of negative charge Robert Millikan –O–O–O–Oil Drop Experiment transferred electrons to oil drop dropped through two plates varying voltage showed that was always a multiple of one small charge –c–calculate mass as 1/1837 the mass of lightest element H

Updated August 2006Created by C. Ippolito August 2006 Proton Eugene Goldstein –u–used modified Crooke’s tube –p–positive rays traveled towards cathode Wilhelm Wien –m–measured charge on proton JJ Thomson –c–charge equal but opposite of electron –c–calculated mass as 1837x that of electron

Updated August 2006Created by C. Ippolito August 2006 Neutron Ernest Rutherford –p–proposed the existence of a third neutral particle James Chadwick –e–established existence of particle with same mass as proton but no charge –n–n–n–neutron