The History of the AtomThe History of the Atom…………..

�� Democritus was the first Democritus was the first to theorize that all to theorize that all matter was composed of matter was composed of atoms!atoms!

�� The name atom comes The name atom comes from his Greek word, from his Greek word, ““ atomosatomos”” , which means , which means not dividable or whole!not dividable or whole!

�� DemocritusDemocritus’’ ideas were ideas were crushed by a another crushed by a another Greek Philosopher, Greek Philosopher, namednamed………………..

………………………………Aristotle!!!!Aristotle!!!!

�� Aristotle asked Aristotle asked Democritus three Democritus three questions:questions:

�� If we are made of atoms, If we are made of atoms, what holds us together?what holds us together?

�� Why canWhy can’’ t we see these t we see these atoms?atoms?

�� Why donWhy don’’ t we fall down t we fall down like a bag of marbles?like a bag of marbles?

Democritus was unable to Democritus was unable to answer these questionsanswer these questions…………..

�� And so, people And so, people continued to think continued to think that matter was that matter was continuous continuous -- your your body, the world body, the world around us was one around us was one continuous piececontinuous piece……..

�� This philosophy This philosophy continued for continued for centuriescenturies…………..

During the middle ages, science During the middle ages, science was lost to the worldwas lost to the world…………

•• The only science that was The only science that was done was performed by done was performed by Arabs (Moors) out of Africa Arabs (Moors) out of Africa that conquered Spain!that conquered Spain!

•• They traveled from the They traveled from the Middle East to Western Middle East to Western Europe, carrying the great Europe, carrying the great library of Alexandria with library of Alexandria with them!them!

•• While the plague and the While the plague and the dark ages were killing dark ages were killing millions, they hadmillions, they had………………....

EVERYTHINGEVERYTHING ……..!..!

�� Running waterRunning water……....

�� DentistryDentistry……....

�� Reading, Writing, Reading, Writing, Geometry, Geometry, CalculusCalculus……

�� BreweriesBreweries…………..

�� Complex gardens Complex gardens and Agricultureand Agriculture ……....

Science did not start up again until the Science did not start up again until the Church was challengedChurch was challenged……..

�� The church was The church was preventing people from preventing people from coming up with new coming up with new ideas and doing science!ideas and doing science!

�� Who were some people Who were some people that challenged the that challenged the Church?Church?

�� Once the Church is Once the Church is challenged by thinkers, challenged by thinkers, science experiments start science experiments start to be done!to be done!

�� With independence, With independence, came independent came independent thought and ideasthought and ideas……....

During the 1700During the 1700’’ s and s and 18001800’’ ss……..

�� Scientists were discovering Scientists were discovering concepts and relationshipsconcepts and relationships

�� Scientists were doing large, Scientists were doing large, observable, basic observable, basic experimentsexperiments

�� They werenThey weren’’ t doing tests t doing tests with microscopes or with microscopes or computers!computers!

�� They were doing They were doing experiments with stoves, experiments with stoves, pots, ovens, and basic pots, ovens, and basic glassware!glassware!

�� With observable properties With observable properties came explanations!came explanations!

Joseph PriestleyJoseph Priestley…………..

�� Prepared pure Prepared pure OxygenOxygen

�� Decomposed Decomposed mercuric oxide into mercuric oxide into mercury and oxygenmercury and oxygen

�� Invented soda popInvented soda pop�� Discovered carbon Discovered carbon

dioxide and nitrous dioxide and nitrous oxide (laughing gas)oxide (laughing gas)

Priestley noticed that the gas produced Priestley noticed that the gas produced by heating mercuric oxide burned a by heating mercuric oxide burned a candle brightlycandle brightly…….. �� He called the air, He called the air, ““ perfect perfect

airair ”” , or , or ““ dephlogisticated dephlogisticated airair ””

�� People thought that People thought that phlogiston was a substance phlogiston was a substance that was in materialsthat was in materials

�� When substances burned, When substances burned, they released phlogiston, they released phlogiston, which eventually caused which eventually caused flames to go out.flames to go out.

�� Is this trueIs this true…….?.?�� He had actually discovered He had actually discovered

oxygen, but didnoxygen, but didn’’ t realize t realize it!it!

Antoine LavoisierAntoine Lavoisier……....

�� Lived during the Lived during the French RevolutionFrench Revolution

�� Was a brilliant Was a brilliant scientist, but a tax scientist, but a tax collectorcollector

�� Had his head Had his head chopped off during chopped off during the revolution with the revolution with royaltyroyalty

Lavoisier Proved…..

�� That substances did not That substances did not give off phlogiston, but give off phlogiston, but used oxygen!used oxygen!

�� He burned metals in the He burned metals in the air, and weighed them air, and weighed them before and afterbefore and after

�� The substances weighed The substances weighed more after, because they more after, because they were combining with were combining with oxygen, not giving off oxygen, not giving off phlogiston!phlogiston!

By weighing the materials By weighing the materials before and afterbefore and after……....�� Lavoisier came up withLavoisier came up with…………....

�� The law of Conservation of MassThe law of Conservation of Mass�� This states:This states:

-- Matter cannot be created or destroyed in Matter cannot be created or destroyed in a chemical reaction, simply converted from one a chemical reaction, simply converted from one form into anotherform into another

�� The extra mass came from the oxygen in the The extra mass came from the oxygen in the air, which he later measured by reheating the air, which he later measured by reheating the compound formedcompound formed

Joseph ProustJoseph Proust……....

�� Examined copper Examined copper carbonatecarbonate

�� No matter the amount, No matter the amount, whenever decomposed it whenever decomposed it would yield 5.3 parts would yield 5.3 parts copper, 4.0 parts oxygen copper, 4.0 parts oxygen and 1.0 parts carbonand 1.0 parts carbon

�� Came up with the law of Came up with the law of definite compositiondefinite composition

�� All substances are All substances are composed of definite composed of definite amounts of each element, amounts of each element, no matter how much or no matter how much or how little of the matter how little of the matter there is!there is!

This compound is This compound is always 5.3 parts Cu, always 5.3 parts Cu, 4.0 parts O, and 1.0 4.0 parts O, and 1.0 parts C!parts C!

John DaltonJohn Dalton…………

�� A schoolteacher!A schoolteacher!

�� Devised the Law of Devised the Law of Multiple ProportionsMultiple Proportions

�� Stated that when two Stated that when two elements form more elements form more than one compound, than one compound, they come together in they come together in whole number whole number ratiosratios…………

WHAT DOES THAT WHAT DOES THAT MEANMEAN ……??

�� Carbon and Oxygen Carbon and Oxygen form two compounds: form two compounds:

�� Carbon dioxide Carbon dioxide -- CC11OO22

�� Carbon monoxide Carbon monoxide -- CC11OO11

�� In carbon dioxide, CIn carbon dioxide, C11OO22, , carbon and oxygen carbon and oxygen combine in a 3 parts to 8 combine in a 3 parts to 8 parts mass ratio parts mass ratio

�� In carbon monoxide, In carbon monoxide, CC11OO11, they do so in a 3 , they do so in a 3 parts to 4 parts mass parts to 4 parts mass ratioratio ……....

�� Seem obviousSeem obvious…….?.?

IT WASNIT WASN ’’ TT…………

�� Scientists didnScientists didn’’ t know t know what was making what was making things come together things come together to react! to react!

�� In fact, They didnIn fact, They didn’’ t t even know that atoms even know that atoms existed!existed!

�� If compounds come If compounds come together in ratios, they together in ratios, they must be made of must be made of smaller pieces!smaller pieces!

John Dalton theorized that John Dalton theorized that these substances were made of these substances were made of atoms!atoms!�� This led toThis led to………………..

THE ATOMIC THEORY OF MATTER!THE ATOMIC THEORY OF MATTER!�� All elements are made of tiny, solid, indestructible particles All elements are made of tiny, solid, indestructible particles

known as atomsknown as atoms�� All atoms of a given element are the sameAll atoms of a given element are the same�� Atoms of different elements are differentAtoms of different elements are different�� Atoms of different elements form compounds in whole Atoms of different elements form compounds in whole

number ratios number ratios -- 1 atom: 1atom, 1 atom: 2 atoms, etc. 1 atom: 1atom, 1 atom: 2 atoms, etc. �� A chemical reaction does not change the atoms themselves, A chemical reaction does not change the atoms themselves,

only how they are combined to form compoundsonly how they are combined to form compounds

BrBr

HH

IIFeFe SS

It took almost 2000 years before It took almost 2000 years before the idea of the atom came back!the idea of the atom came back!�� John Dalton brought John Dalton brought

DemocritusDemocritus’’ idea back!idea back!�� It seems simple, but It seems simple, but

people did not believe people did not believe that matter was made of that matter was made of little marblelittle marble --like like structures called atoms!structures called atoms!

�� John DaltonJohn Dalton’’ s theory was s theory was wrong in one wrong in one respectrespect…………....

Atoms are not solid and Atoms are not solid and indestructible like marblesindestructible like marbles……....

�� They contain different They contain different partsparts…………..

�� However, scientists did However, scientists did not know this until parts not know this until parts of the atom were of the atom were discovereddiscovered……....

�� What part of the atom What part of the atom do you think was do you think was discovered firstdiscovered first……..?..?

THE ELECTRON…!

�� Why do you think it Why do you think it was the first part of was the first part of the atom to be the atom to be discovereddiscovered……..?..?

�� The electron is on the outside of The electron is on the outside of the atom!the atom!

�� The electron is the ONLY part of The electron is the ONLY part of the atom that can be added or the atom that can be added or removed to an atom!removed to an atom!

�� The electron is tiny and light, and The electron is tiny and light, and that is why it can be added or that is why it can be added or removed!removed!

�� This is what we call This is what we call electricityelectricity……moving electrons!moving electrons!

�� Technology wasnTechnology wasn’’ t that good t that good hundreds of years ago!hundreds of years ago!

e- e- e- e- e- e- e- e- e-

The Early 1800’s!

�� Lots of basic work with electricityLots of basic work with electricity�� Matter has charge!Matter has charge!�� There are two types of There are two types of ““ chargecharge”” in the world:in the world:

�� + charged objects+ charged objects�� -- charged objectscharged objects�� Ben Franklin is the first to come up with these names Ben Franklin is the first to come up with these names --

+ and + and --�� Franklin didnFranklin didn’’ t know that these t know that these

charges were part of the atom charges were part of the atom --he didnhe didn’’ t even know that atomst even know that atomsexisted, yet!existed, yet!

Cathode Ray Tube, or Cathode Ray Tube, or CrookeCrooke’’ s Tubes Tube

�� This was one of the very This was one of the very first experiments to be first experiments to be done with electricity! done with electricity!

�� A tube containing two A tube containing two metal electrodes or plates metal electrodes or plates connected to a battery connected to a battery --and all of the gas is sucked and all of the gas is sucked out of the tube!out of the tube!

�� William Crookes designed William Crookes designed this tube in 1879this tube in 1879

�� The cathode ray inside The cathode ray inside glows greenglows green

�� Crookes was convinced this Crookes was convinced this beam consisted of charged beam consisted of charged particlesparticles

So what are Cathode Rays….?

�� J.J. Thomson, in 1897, answered J.J. Thomson, in 1897, answered this question!this question!

�� Thomson used a CrookeThomson used a Crooke’’ s tube s tube and two charged plates above and and two charged plates above and below the beambelow the beam

�� Which way do you think the Which way do you think the beam bentbeam bent…….?.?

�� The Beam was attracted to + The Beam was attracted to + plate, and was deflected from plate, and was deflected from ––plate!plate!

�� From this, he said that the beam From this, he said that the beam was made of negatively charged was made of negatively charged particles, called electrons!particles, called electrons!

�� He was looking at electrons, He was looking at electrons, which are part of the atom!which are part of the atom!

�� These electrons can be easily These electrons can be easily taken off of atoms, and used as taken off of atoms, and used as electricity!electricity!

He also found that a magnet could He also found that a magnet could move the beam as well!move the beam as well!

The cathode ray tube was the beginning to the The cathode ray tube was the beginning to the modern daymodern day……....

TELEVISION!

Black and White….. Color…….

Millikan OilMillikan Oil --Drop Drop ExperimentExperiment

�� Robert Millikan in 1909 figured out the exact charge and mass Robert Millikan in 1909 figured out the exact charge and mass of an electronof an electron

�� He placed oil drops in a box, and hit them with electronsHe placed oil drops in a box, and hit them with electrons

�� The oil drops were sprayed into the upper chamberThe oil drops were sprayed into the upper chamber

�� Some drops gained Some drops gained –– charge (static electricity)charge (static electricity)

e -

e -

e - e -

e -

�� Then Millikan adjusted the Then Millikan adjusted the charge on the plates in the charge on the plates in the bottom of the boxbottom of the box

�� The The -- particles attracted to particles attracted to the upper plate, because it the upper plate, because it was positivewas positive

�� It repelled the bottom plate, It repelled the bottom plate, because it was negativebecause it was negative

�� This suspended the drop in This suspended the drop in spacespace-- he made them float in he made them float in mid air!mid air!

�� From this he calculated the From this he calculated the charge and mass of an charge and mass of an electron, knowing the charge electron, knowing the charge on the plateson the plates

�� The smallest change between The smallest change between two drops was taken to be two drops was taken to be charge of an electroncharge of an electron

e-e-

e-e-

-

+

Now that we have found Now that we have found negative particlesnegative particles……..�� Eugen Goldstein in 1886 used a CrookeEugen Goldstein in 1886 used a Crooke’’ s tube with holes in the s tube with holes in the

negative end and discovered positive particlesnegative end and discovered positive particles�� He shot a cathode beam (beam of electrons) at hydrogen atomsHe shot a cathode beam (beam of electrons) at hydrogen atoms

e-

e-

e- ++ +

+

+

e-

e-

�� The electrons from the atoms went with the The electrons from the atoms went with the beam of electrons to the + platebeam of electrons to the + plate

�� He also saw + particles moving backwards He also saw + particles moving backwards towards the + plate and going through the towards the + plate and going through the holes!holes!

�� He named these + particles He named these + particles ““ protonsprotons”” !!

++

+

Who puts all of this Who puts all of this information together information together into into ““ The Big PictureThe Big Picture”” ??

�� J.J. Thomson theorized that these J.J. Thomson theorized that these negative and positive particles were negative and positive particles were actually part of matter actually part of matter -- part of the part of the atom!atom!

�� We are all made of charge!We are all made of charge!

�� He develops the first working He develops the first working model of the atom, known as the model of the atom, known as the PLUM PUDDING MODEL!PLUM PUDDING MODEL!

�� This rejected DaltonThis rejected Dalton’’ s idea that s idea that atoms were solid particles like atoms were solid particles like marbles that werenmarbles that weren’’ t made of t made of smaller piecessmaller pieces

NOT TRUE!

Why was any of this Why was any of this IMPORTANTIMPORTANT ……??

�� People didnPeople didn’’ t believe in atoms, and didnt believe in atoms, and didn’’ t understand t understand what things like electricity and light were!what things like electricity and light were!

�� Thomson showed that electricity was nothing more Thomson showed that electricity was nothing more than a flow of little negative particles called electrons!than a flow of little negative particles called electrons!

�� And electrons, along with protons, make up every And electrons, along with protons, make up every atom, in every person, plant, building and object in the atom, in every person, plant, building and object in the universeuniverse

�� We are made of charged particles We are made of charged particles -- the same particles the same particles that we use for electricity!that we use for electricity!

Why is ThomsonWhy is Thomson’’ s model s model wrongwrong…….?.?

�� A scientist named Ernest Rutherford figured it out!A scientist named Ernest Rutherford figured it out!�� He shoots big heavy alpha (He shoots big heavy alpha (αααααααα) particles at ultra thin ) particles at ultra thin

gold foilgold foil�� Most of the particles went straight through, and did Most of the particles went straight through, and did

NOTHING.NOTHING.�� A very few were deflected, and some even bounced A very few were deflected, and some even bounced

straight back!straight back!�� Rutherford described this as a bowling ball being Rutherford described this as a bowling ball being

sent at a piece of paper, full speed, and bouncing sent at a piece of paper, full speed, and bouncing back!back!

The Gold Foil ExperimentThe Gold Foil Experiment……..

What is happening? Why are the alpha particles What is happening? Why are the alpha particles bouncing off?bouncing off?

Gold Foil ExperimentGold Foil Experiment……....

What is going onWhat is going on…….?.?�� Most of the alpha particles are going straight through!Most of the alpha particles are going straight through!�� A few of the alpha particles are bouncing off of A few of the alpha particles are bouncing off of

something!something!�� Alpha particles are big, and positive!Alpha particles are big, and positive!�� What could they be bouncing off of?What could they be bouncing off of?�� They must be bouncing off of something that isThey must be bouncing off of something that is……..�� Positive!Positive!�� And big!And big!�� Rutherford theorized that all of the protons werenRutherford theorized that all of the protons weren’’ t t

scattered about, like in a chocolate chip cookie, but scattered about, like in a chocolate chip cookie, but were all concentrated into a tiny, dense center, which were all concentrated into a tiny, dense center, which he called the nucleus!he called the nucleus!

�� The electrons must be orbiting around this nucleus! The electrons must be orbiting around this nucleus! Why?????Why?????

Rutherford’s “nuclear” model!

p+ p+

p+ p+

p+

Nucleus

p+

p+

e-e-

e-

e-

e-e-

e-

What is the relative size of the atom….?

�� An atomic model the size of An atomic model the size of Busch Stadium and parking Busch Stadium and parking would contain a pea sized would contain a pea sized nucleus containing 95.95% of nucleus containing 95.95% of the atoms mass.the atoms mass.

�� The pea at the pitcherThe pea at the pitcher’’ s s mound would be the nucleus, mound would be the nucleus, and an ant crawling on the and an ant crawling on the parking lot outside would be parking lot outside would be an electron!an electron!

�� The atom is mostlyThe atom is mostly……....

�� Empty space! Nothing!Empty space! Nothing!

So is this the final model of the So is this the final model of the atom todayatom today……??

�� No!No!�� A scientist named A scientist named NeilsNeils Bohr, a Bohr, a

great friend of Einstein, noticed great friend of Einstein, noticed something weird about Hydrogensomething weird about Hydrogen

�� A hydrogen atom consists of 1 A hydrogen atom consists of 1 electron orbiting 1 protonelectron orbiting 1 proton……..

�� Atoms can give off light when they Atoms can give off light when they are excited with electricity!are excited with electricity!

�� Think about light bulbs, neon Think about light bulbs, neon lights, headlightslights, headlights……..

�� With one electron, how many With one electron, how many different types of energy or different types of energy or colorscolorsof light do you think hydrogen can of light do you think hydrogen can give offgive off…….?.?

……. Only one . Only one colorcolor of light!of light!�� Bohr excited hydrogen atoms with high voltage electricityBohr excited hydrogen atoms with high voltage electricity�� Hydrogen gave off violet lightHydrogen gave off violet light……..�� The violet light was actually FOUR DIFFERENT COLORS OF The violet light was actually FOUR DIFFERENT COLORS OF

LIGHT, as viewed through a prismLIGHT, as viewed through a prism�� How can one electron give off four How can one electron give off four colorscolors of light???of light???

HOW IS THIS POSSIBLEHOW IS THIS POSSIBLE……??

� It doesn’t make sense that one electron can give off four different colors of light!

� Hydrogen, with only one electron, should be giving off just one color!

� Bohr came up with an explanation for this….

� It involved changing the current accepted model of the atom!

�� It doesnIt doesn’’ t make sense that one electron can give off four different t make sense that one electron can give off four different colorscolors of light!of light!

�� Hydrogen, with only one electron, should be giving off just one Hydrogen, with only one electron, should be giving off just one colorcolor!!

�� Bohr came up with an explanation for thisBohr came up with an explanation for this……..

�� It involved It involved changingchanging the current accepted model of the atom!the current accepted model of the atom!

Bohr came up with a new model for the Bohr came up with a new model for the atomatom……�� Bohr suggested that it electrons could move to many locations Bohr suggested that it electrons could move to many locations

or or ““ energy levelsenergy levels”” within the atom!within the atom!�� The electron was moving to more than one location in the atom!The electron was moving to more than one location in the atom!�� In BohrIn Bohr ’’ s Model of the atom, electrons orbit the nucleus like s Model of the atom, electrons orbit the nucleus like

planets orbit the sun. It is called THE PLANETARY MODEL.planets orbit the sun. It is called THE PLANETARY MODEL.�� When electrons jump up to different energy levels, they When electrons jump up to different energy levels, they

eventually fall back down and give off light!eventually fall back down and give off light!

••Electron can jump up, and Electron can jump up, and when they fall back down, when they fall back down, they give off colors of light!they give off colors of light!

The colors we see for Hydrogen……The The colorscolors we see for we see for HydrogenHydrogen…………

Different Different substances give substances give off different off different colorscolors…….Why?.Why?

CarbonCarbon

HeliumHelium

NeonNeon

Different elements have different electrons, that Different elements have different electrons, that can jump to different places in the atom!can jump to different places in the atom!

Electrons in Energy LevelsElectrons in Energy Levels�� LevelLevel maximum number of maximum number of

electronselectrons�� 11 22�� 22 88�� 33 1818�� 44 3232

Marble ModelMarble ModelPlum Pudding Plum Pudding ModelModel

The Nuclear The Nuclear ModelModel

The Planetary The Planetary ModelModel

Why is learning about the atom important….?�� The atom was considered to be an The atom was considered to be an ““ imaginaryimaginary””

thing, something that people laughed at! thing, something that people laughed at! �� Roosevelt trusted Einstein, and funded his Roosevelt trusted Einstein, and funded his

secret research known as the secret research known as the ““ Manhattan Manhattan ProjectProject””

�� In a few short years, the idea of an invisible In a few short years, the idea of an invisible atom had been developed into a cityatom had been developed into a city--destroying destroying weapon weapon -- the atomic bomb! They figured out the atomic bomb! They figured out they could split atoms apart, and this would they could split atoms apart, and this would release tons of energy!release tons of energy!

In Hiroshima, of a resident civilian population of 250,000 it waIn Hiroshima, of a resident civilian population of 250,000 it was s estimated that 45,000 died on the first day and a further 19,000estimated that 45,000 died on the first day and a further 19,000during the subsequent four months. In Nagasaki, out of a populatduring the subsequent four months. In Nagasaki, out of a population ion of 174,000, 22,000 died on the first day and another 17,000 withof 174,000, 22,000 died on the first day and another 17,000 within four in four months. Over 90% of each city was destroyed.months. Over 90% of each city was destroyed.

Only two atomic bombs have ever been used in wartime history -The U.S. used them both against Japan to end World War II….

Only two atomic bombs have ever been used in wartime history -The U.S. used them both against Japan to end World War II….

The first video shows one of the actual bombs being detonated….The second, the first testing of a “Hydrogen” Bomb…

The first video shows one of the actual bombs being detonated….The second, the first testing of a “Hydrogen” Bomb…