Presentation on theme: "The Development of atomic theory"— Presentation transcript:
1 The Development of atomic theory Chemistry Rules!
2 The Philosophical Era (Circa 500~300BCE) A time when logic ruled the land…This is a good era to do before Chapter 4 officially begins
3 Philosophical Era (Ancient Greece) Two ancient Greeks stand out in the advancement of chemistry.Their ideas were purely based on logic, without experimental support (as was common in that time)
4 Philosophical EraDemocritus ( BCE)The most well-known proponent of the idea that matter was made of small, indivisible particlesCalled the small particles “atomos” meaning “that which cannot be divided”Believed properties of matter came from the properties of the “atomos”
5 Aristotle (384-322 BCE) Famous philosopher of the ancient Greeks Philosophical EraPhilosophical EraAristotle ( BCE)Famous philosopher of the ancient GreeksBelieved matter was comprised of four elementsEarth, Air, Fire, WaterThese elements had a total of four propertiesDry, Moist, Hot, ColdPeople liked him – so this idea stayed
6 Alchemical Era (300 BCE ~ 1400CE) The “Dark Ages” of Chemistry where early chemists had to work in secret and encode their findings for fear of persecutionThis is another good era to do before Chapter 4 officially begins
7 Alchemical EraAlchemythe closest thing to the study of chemistry for nearly two thousand yearsbased on the Aristotelian idea of the four elements of matterIf you change the properties, then you could change elements themselves – lead to gold and immortalityVery mystical study and experimentation with the elements and what was perceived as magicStudy was persecuted, findings hidden in code
8 Procedures of Alchemy Alchemy brought about many lab procedures Alchemical EraProcedures of AlchemyAlchemy brought about many lab proceduresWe use some of the same methods and the names developed in these dark ages of chemistry
9 Alchemical EraElements in AlchemyAlchemists studied many different materials, and their properties, in order to find a way to turn lead into gold and achieve immortality
10 Alchemical symbols for various materials Alchemical EraAlchemical symbols for various materialsAlchemy had to be discussed in secret so that its students could avoid persecution
11 Alchemists’ Persecution Alchemical EraAlchemists’ PersecutionAlchemy was tied to witchcraft and druidsit was perceived as heresy by the catholic churchPractitioners had to hide their trade or hobbyInformation was passed in codeCoded messages were sent between friendsSymbols were used to avoid readable wordsThe growth of Chemistry was stunted by the oppression endured during this era(No such problems in the Far East –Hence gunpowder)Ending the alchemy era with the Flame test lab is a good experience, and a preview for the spectroscopy to come.
12 The Classical Era (1400CE – 1887CE) The printing press heralds the widespread transfer and acquisition of knowledge------This is a good section to do with Chapter 4, sections 1&2 (students read those simultaneously)The Printing Press was invented in Germany, and this lead to the widespread transfer of knowledge in Europe. Other regions were more geographically restricted from this technological advancement.
13 Foundations Robert Boyle departs from Aristotle (1661) Classical EraFoundationsRobert Boyle departs from Aristotle (1661)Suggested in A Skeptical Chymist a substance was not an element if it was made of more than one componentAntoine Lavoisier ( )Accepted Boyle’s idea of elementsDeveloped the concept of compoundsDetermined Law of Conservation of MassLaw: There is no change in mass due to chemical reactionsDiscovered OxygenRecognized Hydrogen as an element
14 Foundations (continued) Classical EraFoundations (continued)Joseph Proust (1790s)Determined the Law of Definite ProportionsElements combine in definite mass ratios to form compoundsRobert BoyleIrishAntoine Lavoisier(and wife)FrenchJoseph ProustFrenchThis slide is a good opportunity to comment on the ethnicity of scientists and how even Lavoisier’s wife was highly involved with chemistry. Note: these are eastern Europeans because the printing press was invented in east Europe.
15 John Dalton [really famous] (1766-1844) Classical EraJohn Dalton [really famous] ( )Dalton returns to Democritus’ ideas in 1803 with four postulatesAll matter is made up of tiny particles called atomsAll atoms of a given element are identical to one another and different from atoms of other elementsAtoms of two or more different elements combine to form compounds. A particular compound is always made up of the same kinds of atoms and the same number of each kind of atom.A chemical reaction involves the rearrangements, separation, or combination of atoms. Atoms are never created or destroyed during a chemical reaction.John DaltonEnglish(Originally poor and self-educated)
16 Defense of Atoms (After Dalton) Classical EraDefense of Atoms (After Dalton)Joseph Gay-Lussac ( )2L hydrogen (g) + 1L Oxygen (g) 2L Water Vapor (g)Experimental findings disagreed with some of Dalton’s beliefsAmadeo Avogadro ( )Suggested Hydrogen and Oxygen are diatomic moleculesThis solved the riddle over Gay-Lussac’s experimental resultsGay-Lussac had the only experiment that seemed to be contrary to Dalton’s ideas. This was unsettling for Dalton, and many people began to seek a way to resolve this issue. Avogadro was the one to suggest a functional response, but living past the Swiss alps, he was at a disadvantage to defend his ideas in the majorly English/French Chemistry forum.Joseph Gay-LussacFrenchAmadeo AvogadroItalian lawyer
17 Dalton’s Disbelief Dalton refused Avogadro's Diatomic molecules Classical EraDalton’s DisbeliefDalton refused Avogadro's Diatomic moleculesDalton wrongly believed that similar types of atoms would repel, like poles of a magnet – hence no diatomsDue to Dalton’s reputation in chemistry, his ideas were believed over Avogadro’sSustaining Dalton’s (wrong) theory, that mass corresponded to amount of atoms, led to confusionAvogadro’s ideas lived on in Italy (south of the Alps)
18 Classical EraAvogadro’s NumberIn 1860 a council of chemists met to solve the problems they had standardizing atomic massesThis was only a problem because they kept Dalton’s idea instead of Avogadro’sAn Italian chemistry teacher, Cannizzaro, presentedHis teaching pamphlet used simple math based on a corollary of Avogadro’s theory– Avogadro's NumberAvogadro's Number grouped atoms into moles: ×1023 parts = 1mole (6.022×1023parts/mole)
19 Classical EraMendeleev’s Table (1869)Once a standard for atomic masses was made, people started to see trendsThese trends showed that properties gradually changed with atomic mass, but seemed to cycle periodicallyDmitri Mendeleev was a Russian teacherHe arranged the elements in a table so that his students could learn more easilyListed atoms by atomic massesNew columns whenever the properties cycledEmpty spots left – He predicted undiscovered elementsDmitri MendeleevRussian teacher
20 Mendeleev’s table quickly became famous Classical EraThe B/W version on the left is one of Mendeleev’s original Russian manuscripts. The image on the right is the same information translated into an English textbook – only a few years later.Mendeleev’s table quickly became famousHere is a black and white copy of the manuscript, and an English textbook version
21 **Don’t Forget Newton!!! (1643-1727) Classical Era**Don’t Forget Newton!!! ( )Isaac Newton was very important to scienceHe is most remembered for his contributions to physics, including gravity and much work in optics (light)He was the first person to divide white light into its partsSplitting light into parts lead to many interesting discoveriesUse spectroscopes of some kind to re-evaluate the flame test labs for their emission spectra. It will likely be a good idea to link this activity to the flame test, but instead use the spectra emission tubes.
22 The Subatomic Era (1897CE – 1932CE) The relatively quick discovery of things smaller than the once “indivisible” atomThis is a good era to do with Chapter 4, section 3
23 It’s Electric! Electricity was studied throughout the classical era Subatomic EraIt’s Electric!Electricity was studied throughout the classical eraBen Franklin’s kite in a thunderstorm (1752)Electricity could flow through gasses (atmosphere)
24 Cathode Ray Tubes Glass chambers used to study electricity in gasses Subatomic EraCathode Ray TubesGlass chambers used to study electricity in gassesCrooke observed glowing rays emitted from the cathodeGlowing rays were observed in all gasses, and even gasless set-ups
25 J.J. Thompson English (1897) Subjected cathode rays to magnetic fields Subatomic EraJ.J. Thompson English (1897)Subjected cathode rays to magnetic fieldsUsing three different arrangements of CRTs he was able to determine that the Cathode rays…Were streams of negatively charged particlesThose particles had very low mass-to-charge ratiosThe observed mass-to-charge ratio was over one thousand times smaller than that of hydrogen ionsThe CRT particles had to be much lighter than hydrogen and/or very highly chargedMass-to-charge ratio of Electron: ×1011C/kgMass-to-charge ratio of Proton (H+):9.578×107C/kgThe schematic depiction of the CRT given here is one of only three types of CRTs that Thompson experimented with. He needed all three types to collect the data needed to get the information he presented. Also, the particular schematic shown here is also a rudimentary schematic for any CRT television. An interesting talking point for students, who may have some experience with the latter.
26 Robert Millikan American (1909) Subatomic EraRobert Millikan American (1909)Thompson needed to know either the mass or the charge of his negative particles to describe themMillikan’s oil drop let him find that the charge on objects is always some multiple of 1.60×10-19CHe proposed this as the basic increment of chargeApplying this charge to Thompson’s particles, he found the mass to be much less than any atomThis is a good time to read the excerpt from the Caltech commencement speech about refining Millikan’s results. It greatly highlights the idea of Scientific Bias and how this affects “real” scientists and what students need to be leery of in their own classroom experiments (and other life scenarios).Find an atomizer – and build this set-up. Learn how to either do it for real as a demonstration, or make it with an illusion good enough that the students can’t tell its fake.
27 Subatomic EraPlumb Pudding Model (1904)With the combined work of Thompson and Millikan the first subatomic particle was established!Electrons – one part of an atom with one negative fundamental increment of electrical chargeSince whole atoms were known to be electrically neutral, Thompson developed the plumb pudding model of the atomPositively (+) charged majorityNegatively (-) Charged electrons
28 Ernest Rutherford New Zealander (1910) Subatomic EraErnest Rutherford New Zealander (1910)Rutherford worked with radiation and had heard of Thompson’s plumb pudding modelHe wanted to use radiation to prove Thompson’s modelHe set-up an alpha particle gun (with help from Marie Curie) to shoot at an ultra-thin piece of gold foil, with a Geiger counter on the other sideThis is another good break to comment on the diversity of people in science. Marie Curie was a BIG DEAL. She had 2 Nobel prizes to be proud of.Ernest RutherfordNew ZealandMarie CuriePolish/ French
29 Rutherford’s Results Rutherford’s results were not what he expected Subatomic EraRutherford’s ResultsRutherford’s results were not what he expectedExpected to have all alpha particles go straight through all of the atomsSaw that occasionally an alpha particle would ricochetDetermined the positive charge of an atom must be held in a massive, centrally located, “nucleus”
30 Subatomic EraThe Second SubatomicAfter more realizations and experiments the second subatomic particle was formally named (1911)Through more Nuclear physics Rutherford determined all atomic nuclei were made up of hydrogen nucleiHydrogen nuclei are deemed ProtonsAntonius van den Broek suggested elements on the periodic table are in order by their increasing number of protons, not Mendeleev’s atomic massesProton: The massive subatomic particle, within the nucleus of an atom, with a single positive charge
31 Subatomic EraThe Planetary Model (1911)Earnest Rutherford took his idea of a nucleus, and the known electrons, to construct a new atomic modelThere is a compact nucleusThe nucleus, made of nucleons, is the location of positive charge in the atomThe charge of the nucleus might be proportional to its massThe orbit of the electrons kept them from falling directly into the nucleus, just like planetary motionThe Rutherford ModelorThe Planetary ModelThe image shows a distinction between two types of particles in the nucleus. Rutherford’s model technically would not have had this – or even possibly known about neutrons. In fact, Rutherford's model was kind of vaguely described even in the article he used to propose it – he was very leery of committing to more than what he absolutely knew to be true about the atom. (He never even said “electron orbits.” That idea was just pieced together from commentary on Rutherford’s model and what came after it.) You can raise questions as to why that may have been a good move…
32 Subatomic EraThe Third Subatomic (1932)Electrons and Protons were identified as particles, but these alone could not fully describe atomsThe charge-to-mass ratio of atoms was off without another additionJames Chadwick studied an unnamed form of radiation– he found it to be electrically neutral and about the mass of a protonIncluding these particles in the nucleus of the atom solved all discrepancies that were previously observedJames ChadwickEnglish
33 Subatomic Review Subatomic Era Electrons Orbit the nucleusVery small mass: ×10−31 kgNegatively charged: − ×10−19 CNucleons: all particles that make up the nucleusProtonsReside in the nucleusRelatively large mass: ×10−27 kgPositively Charged: ×10-19 CNeutronsReside in the NucleusRelatively large mass: ×10−27 kgNo electric charge
34 Atomic Variance An atom’s element is defined by the number of… Protons Subatomic EraAtomic VarianceAn atom’s element is defined by the number of…ProtonsAny atom with a non-neutral charge is called an…IonIons exist because the atom has either more or fewer thanThere are several different forms of elements called that vary in amounts ofElectronsProtonsIsotopesNeutrons
35 The Modern Era (1900CE – Present) The Quark Era starts in 1964, but that advance can be regarded as outside the realm of chemistry – instead a part of nuclear physicsComment on the scope of the course, and how chemistry is distinct from other “nearby” physical sciences.****Warning: Before this era there needs to be a presentation on the nature of light and EM radiation.Chapter 5 in your book!Read pages
36 Modern EraIt all begins… (1900)Scientists believed that we had answered all major questions- only leaving a few items to finishMax Plank was commissioned to build a better light bulbHe wanted to answer questions about “black body radiation”He reluctantly used statistics to solve questions (he was very conservative)December 14, 1900Statistics was a “dirty word” at the time in science. It couldn’t make concrete predictions or descriptive and absolute rules about the world, like calculus could.Max PlankGerman, Physicist
37 Statistics in Science Modern Era Most science uses regular math (ex: F=ma)This era starts to deviate from tradition…The second law of thermodynamics (Boltzmann)All systems move toward a less organized statePlank knew about Boltzmann’s ideas –but disproved of deviation from traditionPlank reluctantly adopted statistics to best explain experimental findings, although he didn’t want to be progressiveEinstein interpreted Plank’s use of statistics to start Quantum theoryHighlight the supremacy of the second law of thermodynamics in chemistry. Inform the students that it is one thing they will have to understand in chemistry. Take the time to comment on the interaction between scientists in this time era – the social aspect of science is important.
38 Quantum Theory Energy can only be transferred in small packets Modern EraQuantum TheoryEnergy can only be transferred in small packetsPlank saw the emission of light could not be explained by classical physics of the dayEnergy transferred in whole-number multiples of hνΔE = energy transferredn = integer multipleν = frequency of lighth = Plank constant (4.134×10-15eV·s )ΔE = nhνContrast this type of math to statistics, and ensure the students know they will be held accountable for basic algebra skills in this class.
39 Modern EraPhoton – light packetsLight partially behaves like particles that Einstein called PhotonsDe Broglie said - all matter can be described by similar wave packetsThis blurred the line between particles and wavesλ=h/pHighlight that this the second time students have seen this slide.
40 λ=h/p …or(λ=h/mv) Wavelength = Plank’s constant / momentum Modern Eraλ=h/p …or(λ=h/mv)Wavelength = Plank’s constant / momentumWavelength – wave propertyPlank’s constant – a fundamental constant× 10-34 m2 kg / sMomentum – a mechanical propertyMomentum = mass × velocity (p=mv)Find the wavelength of lots of things!Highlight that this the second time students have seen this slide.
41 Modern EraExplaining DataThe quantum theory suddenly meant energy could only be transferred in discrete amountsWe had observed emission spectra and knew the Rutherford model, but neither was fully explainedEmission Spectra of Iron (Fe)Define discrete.Emission Spectra of Hydrogen (H)
42 Bohr’s Planetary Model of the Atom Modern EraBohr’s Planetary Model of the Atomintegrated all known information into a new, mathematically based, model of the atomHe kept electrons in orbits around the nucleusOnly allowed certain specific electron orbits for each atomElectron transitions between energy levels (orbits) could only be jumps – nothing could be in between these energy levels (like steps on stairs)Make connection between orbits and energy levels. Be sure that students know that he drew in the lines that Rutherford was not willing to do. His model only worked well for hydrogen atomsNiels BohrDanish Physicist
43 Discrete Electron Energy Levels Modern EraDiscrete Electron Energy LevelsDeBroglie said that electrons always act like wavesThis supported the idea of discrete energy levelsOnly certain wavelengths will “fit” around the atomShake a jump rope with someone, slowly increasing speed. Comment on how not all speeds will create a standing wave, and how this relates to discrete orbits or energy levels.
44 Bohr Energy levels Z2 E=-13.6eV n2 Modern EraBohr Energy levelsElectrons can only travel in specific energy levelsE=-13.6eVZ2n2E = The actual energy of the given energy levelZ = the nuclear charge (number of protons)n=1n=2n=3This linked the properties of atoms with the observations of emission spectrum
45 Bohr Energy Levels Atoms typically found in “Ground State” Modern EraBohr Energy LevelsAtoms typically found in “Ground State”Electrons want to exist in the lowest energy levels availableAtoms can be raised to an “Excited State”Electrons can be put into higher energy levels than usual, but energy has to be added to do soLowest energy levels due to 2nd law of thermodynamics
46 Energy Level Transitions Modern EraEnergy Level TransitionsElectron jump: Quantum leap!Electrons can jump from any lower energy level to a higher energy level and vice versaTotal energy of atom changesLight is absorbed to get to higher energy statesLight is emitted when electrons jump to lower energy states
47 Modern EraElectron TransitionsOnly Specific wavelengths of light are absorbed and emitted by atoms – you have seen these beforeLight emitted by atoms is the emission spectraΔE = Efinal –EinitialE = hνh=Plank’s Constant4.134×10-15eV·s6.63×10-34 m2kg/s
48 Modern EraSome Practice!Colors of light are identified by their frequency and/or wavelengthFind the frequency of light for transitions 1-3Find the wavelength of light for transition 3What does 4 mean?2431
49 Modern EraThe Fall of Bohr…Bohr had easily come up with the best model for the atom so far, and his impact is still felt today but…Werner Heisenberg, a student of Bohr’s, stated:It is impossible to know the absolutely exact position and momentum of anything at the same timeΔx Δp ≥h4πWerner HeisenbergGermany
50 Modern EraThe New Quantum ModelIn 1926 Erwin Schrödinger developed an equation that took care of all inconsistencies of Bohr’s modelCompletely treated electrons as waves (Ψ)Accounted for uncertainty principleThis took the electron from existing in defined orbits to living in a “probability cloud”Concentric probability clouds expand out from the nucleusProbability cloud – the area where an electron is likely to be foundThe above equation is the 1-dimensional Schrödinger equation for the behavior of quantum particles. It is coursely: E=energy, Ψ=wavefunction, V=velocity, ▼(del)= multivariable derivative (since it is squared it is the second derivative), m=mass?
51 The Modern (current) Atom Modern EraThe Modern (current) AtomWe don’t know any electron’s exact location or momentumHeisenberg uncertainty principleWe know electrons act like wavesElectrons are likely to exist in some areas around a nucleus, and not in other areasWe can find probabilities where electrons can be foundErwin SchrödingerAustria
52 Modern EraWhat does it look like?Likely electron locations are now represented by probability clouds – a way to graph probability in three dimensionsElectron CloudsElectronBubblesThe bubble represent the same thing as the clouds, however it is much easier to draw a bubble. So, when graphing this 3-D data the bubble is constructed by choosing an arbitrary point of probability (usually two standard deviations) and drawing in the surface of the bubble at that point of equal probability.
53 Modern EraElectron OrbitalsBubbles are much easier to draw…