Atomic TheoryChapter 4 Section 1

Standards

Imbedded InquiryRecognize that science is a progressive

endeavor that reevaluates and extends what is already accepted.

Standard 1 MatterDescribe the structure and arrangement of

atomic particles.

ObjectivesExplain why Democritus proposed the idea of the atomOutline the five postulates of the atomic theoryExplain the two major experiments of Thomson and Rutherford Compare and contrast Bohr’s model of the atom to the quantum mechanical model of the atomExplain how the atomic theory has changed over the yearsList the contributors to atomic theory, their contributions along with their models of the atom

Beginnings of Atomic Theory

DemocritusGreek philosopher from the 4th centuryFirst to say that universe was made of indivisible particles

He called these atomosAtomos 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

Atomos!

2000 Years After Democritus…

John DaltonEnglish school teacherWrote the Atomic Theory of Matter(Major contribution!)

The 5 postulates of the atomic theory:Elements are made up of particles called atomsThe atoms of a given element are identicalThe atoms of different elements are fundamentally differentCompounds 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. ThomsonExperimenting with electricity in the form of cathode raysFound 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 RutherfordWorked with Thomson on the cathode ray experimentWas 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 spaceModel 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 quantaFirst 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 levelsElectrons orbited the nucleus in these energy levels

Model was the planetary model of the atom

Two Guys with Crazy Names..

Schrödinger and HeisenbergAlso meshed the atomic theory and quantum theory…howeverThey 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 cloudElectron 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 1st to propose atomsDalton wrote atomic theory (which parts are still valid today)Thomson founded electronRutherford founded nucleus (NOT the neutron or the proton these were found later)Bohr first to mesh atomic and quantum theoriesSchrödinger/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 yearsObjective 7: List the contributors to atomic theory, their contributions along with their models of the atom