Atoms and Their Structure Early Greek Theories 400 B.C. - Democritus crushed substances in400 B.C. - Democritus crushed substances in his mortar and.

Atoms and Their Atoms and Their StructureStructure

Early Greek TheoriesEarly Greek Theories

• 400 B.C. - Democritus crushed substances in 400 B.C. - Democritus crushed substances in his mortar and pestlehis mortar and pestle

• There eventually came a point where he could There eventually came a point where he could • not crush the substance anymore (still kept its integrity)not crush the substance anymore (still kept its integrity)

• This became know as the atom. (could not be divided)This became know as the atom. (could not be divided)

Name atomos - indivisibleName atomos - indivisible

Democritus

Democritus’ ModelDemocritus’ Model

solid indestructible sphere

John DaltonJohn Dalton 1800 -Dalton proposed a modern atomic model1800 -Dalton proposed a modern atomic model

based on experimentation not on pure reason.based on experimentation not on pure reason.

• All matter is made of atoms.• Atoms of an element are identical.• Each element has different atoms.• Atoms of different elements combine

in constant ratios to form compounds.• Atoms are rearranged in reactions.

• His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).

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Carbon, CCarbon, C Oxygen, OOxygen, O Carbon Monoxide, COCarbon Monoxide, COMass 12.0Mass 12.0 Mass 16.0Mass 16.0 Mass 12.0 + Mass 16.0Mass 12.0 + Mass 16.0

++++ ====CarbonCarbon OxygenOxygen Carbon Monoxide, Carbon Monoxide,

1:11:1

====Carbon Dioxide, Carbon Dioxide,

1:21:2

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CarbonCarbon OxygenOxygen

11 11

11 22

Law of Constant Composition

John Dalton’s ModelJohn Dalton’s Model

solid indestructible sphere

Parts of AtomsParts of Atoms

J. J. Thomson - English J. J. Thomson - English physicist. 1897physicist. 1897

Used a piece of equipment Used a piece of equipment called a cathode ray tube.called a cathode ray tube.

Thomson’s ExperimentThomson’s Experiment

Voltage Source

+-

Metal Disks

Passing an electric current makes a Passing an electric current makes a beam appear to move from the beam appear to move from the

negative to the positive endnegative to the positive end

Thomson’s ExperimentThomson’s Experiment

Voltage Source

+-

Voltage Source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field he By adding an electric field he found that the moving pieces were found that the moving pieces were

negativenegative

+

-

Thomson’s ModelThomson’s Model Found the Found the

electron.electron. Said the atom was Said the atom was

like like plum puddingplum pudding.. The atom is a The atom is a

sphere with a sphere with a positive charge, positive charge, where negatively where negatively charged pieces charged pieces are embeddedare embedded

Rutherford’s ExperimentRutherford’s Experiment

Ernest Rutherford English Ernest Rutherford English physicist. (1910)physicist. (1910)

Used Alpha particles - (He atom, Used Alpha particles - (He atom, positively charged)positively charged)

Shot them at gold foil which can be Shot them at gold foil which can be made a few atoms thick.made a few atoms thick.

Lead block

Uranium

Gold Foil

Flourescent Screen

He ExpectedHe Expected The alpha The alpha

particles to particles to pass through.pass through.

Because…Because… The positive The positive

charges were charges were spread out spread out evenly. (atom evenly. (atom is neutral)is neutral)

He ExpectedHe Expected

What he got……

+

What he got…..

Rutherford’s ModelRutherford’s Model

Atom is mostly Atom is mostly empty.empty.

Small dense, Small dense, positive piece positive piece at center.at center.

Bohr ModelBohr Model Electrons move in definite Electrons move in definite orbitsorbits

around the nucleus, (like planets around the nucleus, (like planets circle the sun) circle the sun)

These orbits, or energy These orbits, or energy levelslevels, are , are located at certain distances from located at certain distances from the nucleus.the nucleus.

Energy separates one level from Energy separates one level from another.another.

Nucleus

Electron

Orbit

Bohr’s Model

Bohr’s Model

Modern View / Wave Modern View / Wave ModelModel

NucleusNucleus- - protons and protons and neutrons.neutrons.

Electron cloud-Electron cloud- region where region where you ‘might’ find you ‘might’ find an electron.an electron.

The WaveThe Wave ModelModel It is It is impossibleimpossible to determine the to determine the

exact location of an electron. The exact location of an electron. The probableprobable location of an electron location of an electron is based on how much is based on how much energyenergy the electron has.the electron has.

The WaveThe Wave ModelModel