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The Development of The Development of the Atomic Theory the Atomic Theory

The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

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Page 1: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

The Development of the The Development of the Atomic TheoryAtomic Theory

Page 2: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Investigating Atoms and Atomic Investigating Atoms and Atomic TheoryTheory

Students should be able to:Students should be able to:Describe the particle theory of matter. PS.2aDescribe the particle theory of matter. PS.2aUse the Bohr model to differentiate among the Use the Bohr model to differentiate among the

three basic particles in the atom (proton, neutron, three basic particles in the atom (proton, neutron, and electron) and their charges, relative masses, and electron) and their charges, relative masses, and locations. PS.3and locations. PS.3

Compare the Bohr atomic model to the electron Compare the Bohr atomic model to the electron cloud model with respect to their ability to cloud model with respect to their ability to represent accurately the structure of the represent accurately the structure of the atom.PS.3atom.PS.3

Page 3: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Atomic ModelsAtomic Models This model of the This model of the

atom may look atom may look familiar to you. This is familiar to you. This is the Bohr model. In the Bohr model. In this model, the this model, the nucleus is orbited by nucleus is orbited by electrons, which are electrons, which are in different energy in different energy levels. levels. A model uses familiar ideas to A model uses familiar ideas to

explain unfamiliar facts explain unfamiliar facts observed in nature.observed in nature.

A model can be changed as A model can be changed as new information is collected.new information is collected.

Page 4: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Early Theory of an ATOMEarly Theory of an ATOMThe atomic model has The atomic model has

changed throughout changed throughout the centuries, starting the centuries, starting in 400 BC, when it in 400 BC, when it looked like a billiard looked like a billiard ball (solid). ball (solid).

Page 5: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Who are these men?Who are these men?

In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.

Page 6: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

DemocritusDemocritus

This is the Greek philosopher This is the Greek philosopher Democritus who began the Democritus who began the search for a description of search for a description of matter more than matter more than 24002400 years years ago.ago. He asked: Could matter be He asked: Could matter be

divided into smaller and divided into smaller and smaller pieces forever, or smaller pieces forever, or was there a was there a limitlimit to the to the number of times a piece of number of times a piece of matter could be matter could be divideddivided? ?

400 BC

Page 7: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

AtomosAtomos

His theory: Matter could not His theory: Matter could not be divided into smaller and be divided into smaller and smaller pieces forever, smaller pieces forever, eventually the smallest eventually the smallest possible piece would be possible piece would be obtained.obtained.

This piece would be This piece would be indivisible.indivisible.

He named the smallest He named the smallest piece of matter piece of matter ““atomos,atomos,”” meaning meaning ““not to be cut.not to be cut.””

Page 8: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

AtomosAtomos

To Democritus, atoms To Democritus, atoms were were smallsmall, hard , hard particles that were all particles that were all made of the same made of the same material but were material but were differentdifferent shapes and shapes and sizes.sizes.

Atoms were Atoms were infiniteinfinite in in number, always number, always moving and capable of moving and capable of joining together.joining together.

Page 9: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Why?Why?The eminent The eminent

philosophers of philosophers of the time, the time, AristotleAristotle and and Plato, had a Plato, had a more more respected, respected, (and ultimately (and ultimately wrongwrong) theory.) theory.

Aristotle and Plato favored the earth, fire, air and water approach to the nature of matter. Their ideas held sway because of their eminence as philosophers. The atomos idea was buried for approximately 2000 years.

Page 10: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

This This theory was theory was ignored and ignored and forgotten for forgotten for more than more than 2000 2000 years!years!

Page 11: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

DaltonDalton’’s Models Model In the early 1800s, In the early 1800s,

the English the English Chemist John Chemist John Dalton Dalton performed a performed a number of number of experiments that experiments that eventually led to eventually led to the acceptance of the acceptance of the idea of atoms.the idea of atoms.

Page 12: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

DaltonDalton’’s Theorys Theory

He deduced that all He deduced that all elementselements are composed of are composed of atoms. Atoms are atoms. Atoms are indivisible and indivisible and indestructible particles.indestructible particles.

Atoms of the Atoms of the samesame element element are exactly alike.are exactly alike.

Atoms of Atoms of differentdifferent elements elements are are differentdifferent..

CompoundsCompounds are formed by are formed by the joining of atoms of two the joining of atoms of two or more elements.or more elements.

Page 13: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle
Page 14: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

..

This theory This theory became one became one of the of the foundations foundations of modern of modern chemistry.chemistry.

Page 15: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

ThomsonThomson’’s Plum Pudding s Plum Pudding ModelModel

In In 18971897, the , the English scientist English scientist J.J. Thomson J.J. Thomson provided the first provided the first hint that an atom is hint that an atom is made of even made of even smallersmaller particles particles..

Page 16: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

JJ Thomson’s Atomic ModelJJ Thomson’s Atomic Model

He proposed a He proposed a model of the atom model of the atom that is sometimes that is sometimes called the called the ““PlumPlum PuddingPudding”” model. model.

Atoms were made Atoms were made from a positively from a positively chargedcharged substancesubstance with negatively with negatively charged electrons charged electrons scatteredscattered about, like about, like raisins in a pudding.raisins in a pudding.

Page 17: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Thomson ExperimentThomson Experiment

Thomson studied Thomson studied the the passage passage of an of an electric current electric current through a gas.through a gas.

As the current As the current passed through passed through the gas, it gave off the gas, it gave off rays of rays of negatively negatively charged particles.charged particles.

Page 18: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle
Page 19: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Thomson ModelThomson Model

This surprised This surprised Thomson, Thomson, because the because the atoms of the gas atoms of the gas were uncharged. were uncharged. Where had the Where had the negative charges negative charges come from?come from?

Where did they come from?

Page 20: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Thomson concluded that the negative charges came from within the atom.

A particle smaller than an atom had to exist.

The atom was divisible!

Thomson called the negatively charged “corpuscles,” today known as electrons.

Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom.

But he could never find them.

Page 21: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

RutherfordRutherford’’s Gold Foil Experiments Gold Foil Experiment In 1908, the English In 1908, the English

physicist Ernest physicist Ernest Rutherford was hard Rutherford was hard at work on an at work on an experiment that experiment that seemed to have little seemed to have little to do with unraveling to do with unraveling the mysteries of the the mysteries of the atomic structure.atomic structure.

Page 22: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

RutherfordRutherford’’s experiment Involved firing s experiment Involved firing a stream of tiny a stream of tiny positively chargedpositively charged particles at a thin sheet of particles at a thin sheet of gold foilgold foil (2000 atoms thick)(2000 atoms thick)

Page 23: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

GOLD FOIL EXPERIMENTGOLD FOIL EXPERIMENT MostMost of the positively of the positively

charged charged ““bulletsbullets”” passed passed right through the gold right through the gold atoms in the sheet of atoms in the sheet of gold gold foilfoil without changing without changing course at all.course at all.

SomeSome of the positively of the positively charged charged ““bullets,bullets,”” however, however, did bounce away from the did bounce away from the gold sheet as if they had hit gold sheet as if they had hit something something solidsolid. He knew . He knew that positive charges that positive charges repelrepel positive charges.positive charges.

Page 24: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle
Page 25: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

GOLD FOIL ANIMATIONGOLD FOIL ANIMATION

Page 26: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

SIGNIFICANCE OF GOLD FOIL SIGNIFICANCE OF GOLD FOIL EXPERIMENTEXPERIMENT

This could only mean that the gold atoms in the This could only mean that the gold atoms in the sheet were mostly sheet were mostly open spaceopen space. Atoms were . Atoms were notnot a pudding filled with a positively charged a pudding filled with a positively charged material.material.

Rutherford concluded that an atom had a Rutherford concluded that an atom had a small, small, dense, positively charged centerdense, positively charged center that that repelledrepelled his positively charged his positively charged ““bullets.bullets.””

He called the center of the atom the He called the center of the atom the ““nucleusnucleus”” The nucleus is The nucleus is tiny tiny compared to the atom as a compared to the atom as a

whole. whole.

Page 27: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

RutherfordRutherford

Rutherford reasoned Rutherford reasoned that all of an atomthat all of an atom’’s s positively charged positively charged particles were particles were containedcontained in the in the nucleus. The nucleus. The negatively charged negatively charged particles were particles were scatteredscattered outside the outside the nucleus around the nucleus around the atomatom’’s s edgeedge..

Page 28: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

DISCOVERY OF THE DISCOVERY OF THE NEUTRONNEUTRON

In 1932, JAMES In 1932, JAMES CHADWICK CHADWICK discovered the third discovered the third subatomic particle- subatomic particle- the neutron. the neutron.

The neutron has no The neutron has no electrical charge. electrical charge.

The neutron is The neutron is located in the located in the nucleus.nucleus.

Page 29: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Bohr ModelBohr ModelIn 1913, the Danish In 1913, the Danish

scientist Niels Bohr scientist Niels Bohr proposed an proposed an improvement. In his improvement. In his model, he placed model, he placed each electron in a each electron in a specificspecific energy energy level.level.

Page 30: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Bohr ModelBohr Model According to BohrAccording to Bohr’’s s

atomic model, atomic model, electrons move in electrons move in definite definite orbitsorbits around around the nucleus, much the nucleus, much like planets circle the like planets circle the sun. These orbits, or sun. These orbits, or energy energy levelslevels, are , are located at certainlocated at certain distances from the distances from the nucleus.nucleus.

Page 31: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Bohr’s Model of An ATOMBohr’s Model of An ATOM

Page 32: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

HUMAN BOHR MODELHUMAN BOHR MODEL

Page 33: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Wave Model

Page 34: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

The Wave ModelThe Wave Model TodayToday’’s atomic s atomic

model is based on model is based on the principles of the principles of wavewave mechanicsmechanics..

According to the According to the theory of wave theory of wave mechanics, electrons mechanics, electrons do not movedo not move about about an atom in a an atom in a definite definite path,path, like the planets like the planets around the sun.around the sun.

Page 35: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

The Wave ModelThe Wave Model

In fact, it is In fact, it is impossibleimpossible to determine the exact to determine the exact location of an electron. The location of an electron. The probableprobable location of location of an electron is based on how much an electron is based on how much energyenergy the the electron has.electron has.

According to the modern atomic model, at atom According to the modern atomic model, at atom has a has a small positively charged nucleussmall positively charged nucleus surrounded by a large region in which there are surrounded by a large region in which there are enough electrons to make an atom neutral.enough electrons to make an atom neutral.

Page 36: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Electron Cloud:Electron Cloud: A space in which A space in which

electrons are likely to be electrons are likely to be found.found.

Electrons Electrons whirlwhirl about the about the nucleus billions of times nucleus billions of times in one secondin one second

They are not moving They are not moving around in around in set, circularset, circular patterns. Electrons do patterns. Electrons do NOT ORBIT the nucleus.NOT ORBIT the nucleus.

Location of electrons Location of electrons depends upon how much depends upon how much energyenergy the electron has. the electron has.

Page 37: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

Electron Cloud:Electron Cloud:

Depending on their energy they are locked into a Depending on their energy they are locked into a certain area in the cloud.certain area in the cloud.

Electrons with the Electrons with the lowestlowest energy are found in energy are found in the energy level the energy level closestclosest to the nucleus to the nucleus

Electrons with the Electrons with the highesthighest energy are found energy are found in the in the outermostoutermost energy levels, farther from energy levels, farther from the nucleus.the nucleus.

Page 38: The Development of the Atomic Theory. Investigating Atoms and Atomic Theory Students should be able to: Students should be able to: Describe the particle

IndivisibleIndivisible ElectronElectron NucleusNucleus OrbitOrbit Electron Electron CloudCloud

GreekGreek XX

DaltonDalton XX

ThomsonThomson XX

RutherfordRutherford XX XX

BohrBohr XX XX XX

WaveWave XX XX XX