The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small...

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The History of the The History of the Atom Atom By Mrs. By Mrs. Palaski Palaski

Transcript of The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small...

Page 1: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

The History of the AtomThe History of the Atom

By Mrs. PalaskiBy Mrs. Palaski

Page 2: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

IntroductionIntroductionWhat does an atom look like? It is so small What does an atom look like? It is so small

that it cannot be seen. Yet we know there that it cannot be seen. Yet we know there are particles like protons, neutrons and are particles like protons, neutrons and electrons that make up the atom. electrons that make up the atom.

How did scientists discover these subatomic How did scientists discover these subatomic particles? This presentation will take you particles? This presentation will take you through the scientists who contributed to through the scientists who contributed to the discovery of the make-up of the atom.the discovery of the make-up of the atom.

Page 3: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

The Early The Early ChemistsChemists

Page 4: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

GreeksGreeksApproximately 400 B.C., the Greeks Approximately 400 B.C., the Greeks classified matter into four substances.classified matter into four substances.EarthEarthFireFireAirAirWaterWater

Page 5: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

DemocritusDemocritus Greek Greek

philosopherphilosopher Matter consists of Matter consists of

small, indivisible small, indivisible particles called particles called atoms.atoms.

Page 6: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

AristotleAristotle Greek philosopher who Greek philosopher who

opposed Democritus’ opposed Democritus’ beliefsbeliefs

Believed that all matter Believed that all matter was continuous and not was continuous and not made up of smaller made up of smaller particlesparticles

His ideas were accepted His ideas were accepted until the 17until the 17thth century century

Page 7: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

AlchemistsAlchemists Mystics and fakes who claimed that they Mystics and fakes who claimed that they

could turn cheap metals into goldcould turn cheap metals into gold Dominated the next 2000 years of Dominated the next 2000 years of

chemical historychemical history Discovered the elements mercury, Discovered the elements mercury,

antimony, and sulfurantimony, and sulfur Learned to prepare the mineral acids Learned to prepare the mineral acids

hydrochloric, nitric, and sulfuric acidshydrochloric, nitric, and sulfuric acids

Page 8: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Robert BoyleRobert Boyle The first person to The first person to

perform truly perform truly quantitative, physical quantitative, physical experiments using gasesexperiments using gases

Defined Defined elementelement – – something that could not something that could not be broken down into be broken down into two or more simpler two or more simpler substancessubstances

Page 9: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Antoine LavoisierAntoine Lavoisier Father of Modern Father of Modern

ChemistryChemistry Explained that Explained that

combustion involved combustion involved oxygenoxygen

Law of Conservation Law of Conservation of Massof Mass

Page 10: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Law of Conservation Law of Conservation of Massof Mass

Matter is neither destroyed or Matter is neither destroyed or created during ordinary created during ordinary chemical reactions or physical chemical reactions or physical changes.changes.

Mass of reactants (starting Mass of reactants (starting materials) = mass of products materials) = mass of products (end materials)(end materials)

Page 11: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

John DaltonJohn Dalton English school teacher English school teacher

who was fascinated who was fascinated with science with an with science with an intense interest in intense interest in astronomy, which led astronomy, which led to an interest in the to an interest in the gases of the air and gases of the air and their ultimate their ultimate components, atomscomponents, atoms

Page 12: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

John DaltonJohn DaltonFirst to recognize that atoms could First to recognize that atoms could explain the laws of: conservation of explain the laws of: conservation of mass, definite composition and multiple mass, definite composition and multiple proportions proportions Proposed the Atomic Theory in 1803Proposed the Atomic Theory in 1803

Page 13: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Dalton’s Atomic TheoryDalton’s Atomic Theory

1.1. All matter is composed of extremely All matter is composed of extremely small particles called atoms.small particles called atoms.

2.2. Atoms of a given element are Atoms of a given element are identical in size, mass, and other identical in size, mass, and other properties; atoms of different properties; atoms of different elements differ in size, mass, and elements differ in size, mass, and other properties.other properties.

Page 14: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Dalton’s Atomic Theory, Dalton’s Atomic Theory, cont.cont.

3.3. Atoms cannot be subdivided, Atoms cannot be subdivided, created, or destroyed. created, or destroyed.

4. Atoms of different elements can 4. Atoms of different elements can combine in simple, whole-number combine in simple, whole-number ratios to form chemical compounds. ratios to form chemical compounds.

5. In chemical reactions, atoms are 5. In chemical reactions, atoms are combined, separated, or rearranged.combined, separated, or rearranged.

Page 15: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Modern Atomic Modern Atomic TheoryTheory

Dalton’s atomic theory was accepted and Dalton’s atomic theory was accepted and became the basis for further became the basis for further experimentation. experimentation.

There are exceptions to the theory:There are exceptions to the theory:

Atoms CAN be subdivided.Atoms CAN be subdivided.

Atoms of a given element may have Atoms of a given element may have different masses, they are called different masses, they are called

isotopes.isotopes.

Page 16: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Dalton’s Model of the AtomDalton’s Model of the Atom

Dalton developed a model of the atom Dalton developed a model of the atom based on his atomic theory. He felt based on his atomic theory. He felt the atom was an extremely small, the atom was an extremely small, indivisible particle. indivisible particle.

His model of the atom is called the His model of the atom is called the homogeneous spheres or the Billiard homogeneous spheres or the Billiard Ball Model. Ball Model.

Page 17: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Early Early Experiments to Experiments to Characterize Characterize

the Atomthe Atom

Page 18: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

The ElectronThe Electron

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Sir William CrookesSir William Crookes Developed the Crooke’s tube – a tube that Developed the Crooke’s tube – a tube that

produces cathode raysproduces cathode rays Noticed that the rays moved from the Noticed that the rays moved from the

cathode to the anodecathode to the anode Found that rays traveled in straight lines Found that rays traveled in straight lines

and possessed energyand possessed energy Concluded that the stream of light was Concluded that the stream of light was

made up of particlesmade up of particles

Page 20: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

J.J. ThomsonJ.J. Thomson Experimented with a CRT Experimented with a CRT

(cathode ray tube)(cathode ray tube) A CRT is an evacuated A CRT is an evacuated

glass bulb containing two glass bulb containing two ends: the cathode and the ends: the cathode and the anode.anode.

Page 21: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Cathode Ray TubeCathode Ray Tube

An electrical current passes through the An electrical current passes through the tube from the cathode (negative end) to tube from the cathode (negative end) to the anode (positive end).the anode (positive end).

Page 22: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Cathode Ray TubeCathode Ray Tube A magnet was applied to these rays and always A magnet was applied to these rays and always

with the same results:with the same results:

Negative end of magnet repelled cathode ray;Negative end of magnet repelled cathode ray;

Positive end of magnet attracted cathode rays.Positive end of magnet attracted cathode rays. Thomson noticed that the cathode rays were the Thomson noticed that the cathode rays were the

same same regardlessregardless of the element or metal used to of the element or metal used to make-up the cathode.make-up the cathode.

Page 23: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Discovery from CRTDiscovery from CRT

Thomson concluded that the Thomson concluded that the cathode ray was a stream of cathode ray was a stream of negatively charged particles, negatively charged particles, which he called electrons.which he called electrons.

Determined ratio of particle’s Determined ratio of particle’s electrical charge to mass electrical charge to mass (e/m(e/m))..

Page 24: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Thomson’s ConclusionThomson’s Conclusion Thomson concluded that all atoms of all Thomson concluded that all atoms of all

substances contain the same kind of substances contain the same kind of negative particles, and all electrons are negative particles, and all electrons are identical.identical.

Thomson discovered the ELECTRONS.Thomson discovered the ELECTRONS.

Plum Pudding model is Thomson’s model Plum Pudding model is Thomson’s model of the atom. It is called the plum pudding of the atom. It is called the plum pudding model because he pictured the electrons model because he pictured the electrons dispersed like raisins in a pudding.dispersed like raisins in a pudding.

Page 25: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Plum Pudding ModelPlum Pudding Model Plum Pudding model is Thomson’s model Plum Pudding model is Thomson’s model

of the atom. of the atom. The atom consists of a diffuse cloud of The atom consists of a diffuse cloud of

positive charge with negative electrons positive charge with negative electrons embedded randomly in it.embedded randomly in it.

It is called the plum pudding model It is called the plum pudding model because he pictured the electrons because he pictured the electrons dispersed like raisins in a pudding.dispersed like raisins in a pudding.

Page 26: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Plum Pudding ModelPlum Pudding Model

+

+

+

++

+

+

Negative electrons

Page 27: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Robert MillikanRobert Millikan Performed the Oil Performed the Oil

Drop Experiment Drop Experiment (1909)(1909)

Work contained Work contained excellent precisionexcellent precision

Determined the exact Determined the exact charge and exact mass charge and exact mass of an electronof an electron

Page 28: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Oil Drop ExperimentOil Drop Experiment

Page 29: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

How the Oil Drop How the Oil Drop Experiment WorkedExperiment Worked

A fine mist of oil is sprayed into the chamber.A fine mist of oil is sprayed into the chamber. A few oil drops will fall through the hole in A few oil drops will fall through the hole in

the positively charged plate at the top.the positively charged plate at the top. As the oil drops fall due to gravity, they As the oil drops fall due to gravity, they

acquire extra electrons which are dislodged acquire extra electrons which are dislodged from gases in the air by X rays.from gases in the air by X rays.

As the charged oil drops descend, the As the charged oil drops descend, the electrically charged plates are turned on.electrically charged plates are turned on.

Page 30: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

How the Oil Drop How the Oil Drop Experiment WorkedExperiment Worked

The oil drops now have two forces acting on The oil drops now have two forces acting on them. Gravity and electrical charge.them. Gravity and electrical charge.

Using the microscope to observe the oil Using the microscope to observe the oil drops, Millikan could determine the charge drops, Millikan could determine the charge needed to suspend the drops in mid-air.needed to suspend the drops in mid-air.

Millikan calculated the:Millikan calculated the:

exact mass (9.109 x 10exact mass (9.109 x 10-31-31 kilograms) and kilograms) and charge (-1.6 x 10charge (-1.6 x 10-19-19 coulombs) of an electron. coulombs) of an electron.

Page 31: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Results of CRT and Oil Results of CRT and Oil Drop ExperimentDrop Experiment

1.1. Proved that atoms are divisible.Proved that atoms are divisible.

2.2. Atoms are electrically neutral Atoms are electrically neutral therefore they must have a positive therefore they must have a positive charge equal to the negative charge.charge equal to the negative charge.

3.3. Since electrons have such a small Since electrons have such a small mass, atoms must have additional mass, atoms must have additional particles to account for most of their particles to account for most of their mass.mass.

Page 32: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Oil Drop ExperimentOil Drop Experiment

http://physics.wku.edu/~womble/phys260/millikan.html

Page 33: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Eugene GoldsteinEugene Goldstein

In 1885, Goldstein used a canal ray tube In 1885, Goldstein used a canal ray tube filled with hydrogen to discover protons. filled with hydrogen to discover protons.

He called them “canal rays.”He called them “canal rays.”

Page 34: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Ernest RutherfordErnest Rutherford Thought that the Thought that the

atom was all atom was all empty spaceempty space

In 1908, he carried In 1908, he carried out an experiment out an experiment to test Thomson’s to test Thomson’s plum pudding plum pudding model.model.

Page 35: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Gold Foil ExperimentGold Foil Experiment

Used alpha particles as bulletsUsed alpha particles as bullets Shot the alpha particles at a thin sheet of gold foilShot the alpha particles at a thin sheet of gold foil Predicted the alpha particles would pass straight Predicted the alpha particles would pass straight

throughthrough

Page 36: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Results of Gold Foil Results of Gold Foil ExperimentExperiment

Almost all of the particles passed Almost all of the particles passed straight through.straight through.

Some were deflected. (1 in 10,000)Some were deflected. (1 in 10,000) 1 in 20,000 were reflected straight 1 in 20,000 were reflected straight

backback Results caused Rutherford to Results caused Rutherford to

formulate a new model of the atom.formulate a new model of the atom.

Page 37: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Gold Foil ExperimentGold Foil Experiment

Rutherford said it was “as if you had fired a 15-inch Rutherford said it was “as if you had fired a 15-inch (artillery) shell at a piece of tissue paper and it came back (artillery) shell at a piece of tissue paper and it came back and hit you.”and hit you.”

Why did this happen?Why did this happen? Rutherford reasoned that the fast-moving particles must be Rutherford reasoned that the fast-moving particles must be

repelled by some powerful force within the atom. Also, repelled by some powerful force within the atom. Also, whatever caused this repulsion must occupy a very small whatever caused this repulsion must occupy a very small amount of space since only a very few particles ran into it.amount of space since only a very few particles ran into it.

Results caused Rutherford to formulate a new model of Results caused Rutherford to formulate a new model of the atom.the atom.

Page 38: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

The NucleusThe Nucleus

Page 39: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

So how small So how small isis the the nucleus?nucleus?

How large is an atom’s volume compared to its How large is an atom’s volume compared to its nucleus?nucleus?

Think of a football field and place a dime in the Think of a football field and place a dime in the center of the 50 yard line.center of the 50 yard line.

Page 40: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Rutherford’s Model of the Rutherford’s Model of the AtomAtom

Rutherford’s model of the atom is the Rutherford’s model of the atom is the nuclear model.nuclear model.

There is a very small, dense center of There is a very small, dense center of concentrated charge, called the nucleus.concentrated charge, called the nucleus.

Rutherford concluded that the atom is Rutherford concluded that the atom is mostlymostly empty space. empty space.

Electrons must be present in the empty Electrons must be present in the empty space about the nucleus to maintain the space about the nucleus to maintain the neutrality of matter.neutrality of matter.

Page 41: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Nuclear Model of the AtomNuclear Model of the Atom

NucleusNucleus

-

-

-

-

-

-

-

-

-

-Nucleus is positively charged.

- electrons

Page 42: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

A PuzzleA Puzzle

Electrons must be present in the empty Electrons must be present in the empty space about the nucleus to maintain the space about the nucleus to maintain the neutrality of matter.neutrality of matter.

If an atom has a positive center and the If an atom has a positive center and the negative electrons are on the outside of the negative electrons are on the outside of the atom, why don’t the electrons fall into the atom, why don’t the electrons fall into the center?center?

Centripetal forceCentripetal force

Page 43: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Niels BohrNiels Bohr

Studied under Ernest Studied under Ernest RutherfordRutherford

In 1913, he developed his In 1913, he developed his own structure of the atom own structure of the atom based on Rutherford’s theory. based on Rutherford’s theory.

Rutherford had shown that Rutherford had shown that the atom consisted of a the atom consisted of a positively charged nucleus positively charged nucleus with negative electrons in with negative electrons in orbit around it.orbit around it.

Page 44: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

BohrBohr

Bohr expanded this theory by suggesting that Bohr expanded this theory by suggesting that electrons travel in specific successively larger electrons travel in specific successively larger orbits or paths around the nucleus which he orbits or paths around the nucleus which he called energy levels. These energy levels are called energy levels. These energy levels are designated distances from the nucleus in which designated distances from the nucleus in which electrons may be found. electrons may be found.

He suggested that outer orbits could hold more He suggested that outer orbits could hold more electrons than the inner ones, and that these outer electrons than the inner ones, and that these outer orbits determine the atom’s chemical properties.orbits determine the atom’s chemical properties.

Page 45: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

Planetary Model of the AtomPlanetary Model of the Atom

Nucleus

e -

e -

e -

e -

Page 46: The History of the Atom By Mrs. Palaski. Introduction What does an atom look like? It is so small that it cannot be seen. Yet we know there are particles.

James ChadwickJames Chadwick

Discovered the neutron Discovered the neutron in 1932in 1932

The neutron is a particle The neutron is a particle in the nucleus that has in the nucleus that has about the same mass as about the same mass as a proton, but has no a proton, but has no charge. charge.