Atomic Theory Chapter 4 Section 1

Standards  Imbedded Inquiry  Recognize that science is a progressive endeavor that reevaluates and extends what is already accepted.  Standard 1 Matter  Describe the structure and arrangement of atomic particles.

Objectives Explain why Democritus proposed the idea of the atom Outline the five postulates of the atomic theory Explain the two major experiments of Thomson and Rutherford Compare and contrast Bohr’s model of the atom to the quantum mechanical model of the atom Explain how the atomic theory has changed over the years List the contributors to atomic theory, their contributions along with their models of the atom

Beginnings of Atomic Theory Democritus Greek philosopher from the 4 th century First to say that universe was made of indivisible particles He called these atomos Atomos means unable to cut or divide Most people in his time thought that he was crazy…so why do you think that he proposed this? Reason: it explained the changes in matter that he observed Democritus was not a scientist…so he did not have proof of his theory Of course now days we know for a fact that atoms are real and that everything is made up of these atoms! Objective 1: Explain why Democritus proposed the idea of the atom

2000 Years After Democritus… John Dalton English school teacher Wrote the Atomic Theory of Matter( Major contribution!) The 5 postulates of the atomic theory: Elements are made up of particles called atoms The atoms of a given element are identical The atoms of different elements are fundamentally different Compounds are formed when different elements combine Chemical reactions involve reorganizing atoms, not changing what they are Model was known as…the billiard ball Objective 2: Outline the five postulates of the atomic theory

The Physicist…Some 70 Years Later… J. J. Thomson Experimenting with electricity in the form of cathode rays Found that cathode rays moved away from a magnet in the positive direction… Conclusion: cathode rays are made of negatively charged particles that must come from the inside of an atom What had Thomson’s cathode ray experiment discovered? The electron!(Thomson’s contribution) Thomson’s model for the atom was known as the plum-pudding model Objective 3: Explain the two major experiments of Thomson and Rutherford

Thomson’s Research Apprentice… Ernest Rutherford Worked with Thomson on the cathode ray experiment Was testing Thomson’s model with an experiment known as the Gold Foil experiment Shot positive alpha particles into a thin sheet of gold foil Found that most particles went straight through, but there were a few that actually bounced back! What did Rutherford discover? The NUCLEUS!! Proposed that the atom was made of a dense center known as the nucleus but mostly consisted of empty space Model of the atom was the nuclear model Objective 3: Explain the two major experiments of Thomson and Rutherford

Objective 5: Compare and contrast Bohr’s model of the atom to the quantum mechanical model of the atom The Guy with the Bohring Name… Neils Bohr Worked on quantum theory Theory that light and other small particles emit packets of energy known as quanta First to mesh the quantum theory with the atomic theory (Bohr’s contribution) Based off the emission spectrum of hydrogen Suggested that electrons are found in certain energy levels Electrons orbited the nucleus in these energy levels Model was the planetary model of the atom

Two Guys with Crazy Names.. Schrödinger and Heisenberg Also meshed the atomic theory and quantum theory…however They did not mesh it to one element they wanted to explain all the elements… Both came up with complex mathematic equations and explanations as to why elements emitted certain colors of light (their contributions) They found that… Electrons are located in an electron cloud Electron cloud is the probable location of the electrons Model was known as the quantum mechanical model (this is the model still used today) Objective 4: Compare and contrast Bohr’s model of the atom to the quantum mechanical model of the atom

In Review… Atomic theory has changed over time Democritus 1 st to propose atoms Dalton wrote atomic theory (which parts are still valid today) Thomson founded electron Rutherford founded nucleus (NOT the neutron or the proton these were found later) Bohr first to mesh atomic and quantum theories Schrödinger/Heisenberg came up with the complicated mathematics behind the quantum mechanical model of the atom All of these people helped to form the modern atomic theory, and all contributed certain points that are still valid today Objective 6: Explain how the atomic theory has changed over the years Objective 7: List the contributors to atomic theory, their contributions along with their models of the atom