Historical Atomic ModelsHistorical Atomic Models

ABC II BABC II B

Ms. PollockMs. Pollock

Spring 2007Spring 2007

DemocritusDemocritus

Democritus’s Theory of Democritus’s Theory of Atomic StructureAtomic Structure

First to propose atomic theoryFirst to propose atomic theory 400 BCE400 BCE Atoms “atomos” are indivisible.Atoms “atomos” are indivisible. Leads to Aristotle’s belief that Leads to Aristotle’s belief that

matter is made of 4 elements – matter is made of 4 elements – earth, air, water, and fireearth, air, water, and fire

John DaltonJohn Dalton

Dalton’s Atomic TheoryDalton’s Atomic Theory

1806 published 1806 published theorytheory

English teacher and English teacher and climatologistclimatologist

QuakerQuaker Discovered color Discovered color

blindnessblindness Very careful, Very careful,

repeatable repeatable measurementsmeasurements

Dalton’s Atomic TheoryDalton’s Atomic Theory

Elements made of tiny particles, called Elements made of tiny particles, called atomsatoms

All atoms of given element identicalAll atoms of given element identical Elements of different atoms different Elements of different atoms different

from each otherfrom each other Atoms combined to make compoundsAtoms combined to make compounds Atoms not able to be created or Atoms not able to be created or

divided; only recombined in a reactiondivided; only recombined in a reaction

William CrookesWilliam Crookes

Crookes’ TubeCrookes’ Tube

Developed cathode-ray tubesDeveloped cathode-ray tubes– Control of electron beamControl of electron beam– Discovery of new particles inside Discovery of new particles inside

atomsatoms Device used in televisionsDevice used in televisions Discovery of thallium and heliumDiscovery of thallium and helium

Crookes TubeCrookes Tube

J. J. ThomsonJ. J. Thomson

Thomson and the AtomThomson and the Atom

Plum Pudding Plum Pudding ModelModel

Discovered Discovered electron in 1897electron in 1897

Found cathode Found cathode rays would bend rays would bend toward positive toward positive charge, so must charge, so must be negativebe negative

Ernest RutherfordErnest Rutherford

Rutherford’s ContributionRutherford’s Contribution

Discovered large Discovered large positive charge in positive charge in center of atomcenter of atom

Gold foil Gold foil experimentexperiment

Discovered protonDiscovered proton 19091909

Niels BohrNiels Bohr

Bohr ModelsBohr Models

Electrons orbiting Electrons orbiting nucleus in special nucleus in special orbitsorbits

Nucleus very smallNucleus very small 19131913 Electrons only Electrons only

found in certain found in certain places in the atomplaces in the atom

Albert EinsteinAlbert Einstein

EinsteinEinstein

Much energy released from small Much energy released from small amounts of matteramounts of matter

E = mcE = mc22

Aided in development of atomic Aided in development of atomic bombbomb

Connection of many physics Connection of many physics theories and beliefs through one theories and beliefs through one formulaformula

Max PlanckMax Planck

PlanckPlanck

Father of quantum mechanicsFather of quantum mechanics Energy not continuous, released in Energy not continuous, released in

quantaquanta Developed universal constant of Developed universal constant of

energyenergy Calculated energy based on Calculated energy based on

electromagnetic frequency and electromagnetic frequency and constantconstant