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The Development of atomic theory

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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 Era Democritus ( BCE) The most well-known proponent of the idea that matter was made of small, indivisible particles Called 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 Era Philosophical Era Aristotle ( BCE) Famous philosopher of the ancient Greeks Believed matter was comprised of four elements Earth, Air, Fire, Water These elements had a total of four properties Dry, Moist, Hot, Cold People 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 persecution This is another good era to do before Chapter 4 officially begins

7 Alchemical Era Alchemy the closest thing to the study of chemistry for nearly two thousand years based on the Aristotelian idea of the four elements of matter If you change the properties, then you could change elements themselves – lead to gold and immortality Very mystical study and experimentation with the elements and what was perceived as magic Study was persecuted, findings hidden in code

8 Procedures of Alchemy Alchemy brought about many lab procedures
Alchemical Era Procedures of Alchemy Alchemy brought about many lab procedures We use some of the same methods and the names developed in these dark ages of chemistry

9 Alchemical Era Elements in Alchemy Alchemists 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 Era Alchemical symbols for various materials Alchemy had to be discussed in secret so that its students could avoid persecution

11 Alchemists’ Persecution
Alchemical Era Alchemists’ Persecution Alchemy was tied to witchcraft and druids it was perceived as heresy by the catholic church Practitioners had to hide their trade or hobby Information was passed in code Coded messages were sent between friends Symbols were used to avoid readable words The 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 Era Foundations Robert Boyle departs from Aristotle (1661) Suggested in A Skeptical Chymist a substance was not an element if it was made of more than one component Antoine Lavoisier ( ) Accepted Boyle’s idea of elements Developed the concept of compounds Determined Law of Conservation of Mass Law: There is no change in mass due to chemical reactions Discovered Oxygen Recognized Hydrogen as an element

14 Foundations (continued)
Classical Era Foundations (continued) Joseph Proust (1790s) Determined the Law of Definite Proportions Elements combine in definite mass ratios to form compounds Robert Boyle Irish Antoine Lavoisier (and wife) French Joseph Proust French This 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 Era John Dalton [really famous] ( ) Dalton returns to Democritus’ ideas in 1803 with four postulates All matter is made up of tiny particles called atoms All atoms of a given element are identical to one another and different from atoms of other elements Atoms 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 Dalton English (Originally poor and self-educated)

16 Defense of Atoms (After Dalton)
Classical Era Defense 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 beliefs Amadeo Avogadro ( ) Suggested Hydrogen and Oxygen are diatomic molecules This solved the riddle over Gay-Lussac’s experimental results Gay-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-Lussac French Amadeo Avogadro Italian lawyer

17 Dalton’s Disbelief Dalton refused Avogadro's Diatomic molecules
Classical Era Dalton’s Disbelief Dalton refused Avogadro's Diatomic molecules Dalton wrongly believed that similar types of atoms would repel, like poles of a magnet – hence no diatoms Due to Dalton’s reputation in chemistry, his ideas were believed over Avogadro’s Sustaining Dalton’s (wrong) theory, that mass corresponded to amount of atoms, led to confusion Avogadro’s ideas lived on in Italy (south of the Alps)

18 Classical Era Avogadro’s Number In 1860 a council of chemists met to solve the problems they had standardizing atomic masses This was only a problem because they kept Dalton’s idea instead of Avogadro’s An Italian chemistry teacher, Cannizzaro, presented His teaching pamphlet used simple math based on a corollary of Avogadro’s theory– Avogadro's Number Avogadro's Number grouped atoms into moles: ×1023 parts = 1mole (6.022×1023parts/mole)

19 Classical Era Mendeleev’s Table (1869) Once a standard for atomic masses was made, people started to see trends These trends showed that properties gradually changed with atomic mass, but seemed to cycle periodically Dmitri Mendeleev was a Russian teacher He arranged the elements in a table so that his students could learn more easily Listed atoms by atomic masses New columns whenever the properties cycled Empty spots left – He predicted undiscovered elements Dmitri Mendeleev Russian teacher

20 Mendeleev’s table quickly became famous
Classical Era The 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 famous Here 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 science He 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 parts Splitting light into parts lead to many interesting discoveries Use 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” atom This is a good era to do with Chapter 4, section 3

23 It’s Electric! Electricity was studied throughout the classical era
Subatomic Era It’s Electric! Electricity was studied throughout the classical era Ben 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 Era Cathode Ray Tubes Glass chambers used to study electricity in gasses Crooke observed glowing rays emitted from the cathode Glowing rays were observed in all gasses, and even gasless set-ups

25 J.J. Thompson English (1897) Subjected cathode rays to magnetic fields
Subatomic Era J.J. Thompson English (1897) Subjected cathode rays to magnetic fields Using three different arrangements of CRTs he was able to determine that the Cathode rays… Were streams of negatively charged particles Those particles had very low mass-to-charge ratios The observed mass-to-charge ratio was over one thousand times smaller than that of hydrogen ions The CRT particles had to be much lighter than hydrogen and/or very highly charged Mass-to-charge ratio of Electron: ×1011C/kg Mass-to-charge ratio of Proton (H+):9.578×107C/kg The 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 Era Robert Millikan American (1909) Thompson needed to know either the mass or the charge of his negative particles to describe them Millikan’s oil drop let him find that the charge on objects is always some multiple of 1.60×10-19C He proposed this as the basic increment of charge Applying this charge to Thompson’s particles, he found the mass to be much less than any atom This 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 Era Plumb 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 charge Since whole atoms were known to be electrically neutral, Thompson developed the plumb pudding model of the atom Positively (+) charged majority Negatively (-) Charged electrons

28 Ernest Rutherford New Zealander (1910)
Subatomic Era Ernest Rutherford New Zealander (1910) Rutherford worked with radiation and had heard of Thompson’s plumb pudding model He wanted to use radiation to prove Thompson’s model He 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 side This 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 Rutherford New Zealand Marie Curie Polish/ French

29 Rutherford’s Results Rutherford’s results were not what he expected
Subatomic Era Rutherford’s Results Rutherford’s results were not what he expected Expected to have all alpha particles go straight through all of the atoms Saw that occasionally an alpha particle would ricochet Determined the positive charge of an atom must be held in a massive, centrally located, “nucleus”

30 Subatomic Era The Second Subatomic After 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 nuclei Hydrogen nuclei are deemed Protons Antonius van den Broek suggested elements on the periodic table are in order by their increasing number of protons, not Mendeleev’s atomic masses Proton: The massive subatomic particle, within the nucleus of an atom, with a single positive charge

31 Subatomic Era The Planetary Model (1911) Earnest Rutherford took his idea of a nucleus, and the known electrons, to construct a new atomic model There is a compact nucleus The nucleus, made of nucleons, is the location of positive charge in the atom The charge of the nucleus might be proportional to its mass The orbit of the electrons kept them from falling directly into the nucleus, just like planetary motion The Rutherford Model or The Planetary Model The 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 Era The Third Subatomic (1932) Electrons and Protons were identified as particles, but these alone could not fully describe atoms The charge-to-mass ratio of atoms was off without another addition James Chadwick studied an unnamed form of radiation– he found it to be electrically neutral and about the mass of a proton Including these particles in the nucleus of the atom solved all discrepancies that were previously observed James Chadwick English

33 Subatomic Review Subatomic Era Electrons
Orbit the nucleus Very small mass: ×10−31 kg Negatively charged: − ×10−19 C Nucleons: all particles that make up the nucleus Protons Reside in the nucleus Relatively large mass: ×10−27 kg Positively Charged: ×10-19 C Neutrons Reside in the Nucleus Relatively large mass: ×10−27 kg No electric charge

34 Atomic Variance An atom’s element is defined by the number of… Protons
Subatomic Era Atomic Variance An atom’s element is defined by the number of… Protons Any atom with a non-neutral charge is called an… Ion Ions exist because the atom has either more or fewer than There are several different forms of elements called that vary in amounts of Electrons Protons Isotopes Neutrons

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 physics Comment 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 Era It all begins… (1900) Scientists believed that we had answered all major questions- only leaving a few items to finish Max Plank was commissioned to build a better light bulb He wanted to answer questions about “black body radiation” He reluctantly used statistics to solve questions (he was very conservative) December 14, 1900 Statistics 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 Plank German, 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 state Plank knew about Boltzmann’s ideas –but disproved of deviation from tradition Plank reluctantly adopted statistics to best explain experimental findings, although he didn’t want to be progressive Einstein interpreted Plank’s use of statistics to start Quantum theory Highlight 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 Era Quantum Theory Energy can only be transferred in small packets Plank saw the emission of light could not be explained by classical physics of the day Energy transferred in whole-number multiples of hν ΔE = energy transferred n = integer multiple ν = frequency of light h = Plank constant (4.134×10-15eV·s ) ΔE = nhν Contrast 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 Era Photon – light packets Light partially behaves like particles that Einstein called Photons De Broglie said - all matter can be described by similar wave packets This blurred the line between particles and waves λ=h/p Highlight that this the second time students have seen this slide.

40 λ=h/p …or(λ=h/mv) Wavelength = Plank’s constant / momentum
Modern Era λ=h/p …or(λ=h/mv) Wavelength = Plank’s constant / momentum Wavelength – wave property Plank’s constant – a fundamental constant × 10-34 m2 kg / s Momentum – a mechanical property Momentum = mass × velocity (p=mv) Find the wavelength of lots of things! Highlight that this the second time students have seen this slide.

41 Modern Era Explaining Data The quantum theory suddenly meant energy could only be transferred in discrete amounts We had observed emission spectra and knew the Rutherford model, but neither was fully explained Emission Spectra of Iron (Fe) Define discrete. Emission Spectra of Hydrogen (H)

42 Bohr’s Planetary Model of the Atom
Modern Era Bohr’s Planetary Model of the Atom integrated all known information into a new, mathematically based, model of the atom He kept electrons in orbits around the nucleus Only allowed certain specific electron orbits for each atom Electron 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 atoms Niels Bohr Danish Physicist

43 Discrete Electron Energy Levels
Modern Era Discrete Electron Energy Levels DeBroglie said that electrons always act like waves This supported the idea of discrete energy levels Only certain wavelengths will “fit” around the atom Shake 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 Era Bohr Energy levels Electrons can only travel in specific energy levels E=-13.6eV Z2 n2 E = The actual energy of the given energy level Z = the nuclear charge (number of protons) n=1 n=2 n=3 This linked the properties of atoms with the observations of emission spectrum

45 Bohr Energy Levels Atoms typically found in “Ground State”
Modern Era Bohr Energy Levels Atoms typically found in “Ground State” Electrons want to exist in the lowest energy levels available Atoms 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 so Lowest energy levels due to 2nd law of thermodynamics

46 Energy Level Transitions
Modern Era Energy Level Transitions Electron jump: Quantum leap! Electrons can jump from any lower energy level to a higher energy level and vice versa Total energy of atom changes Light is absorbed to get to higher energy states Light is emitted when electrons jump to lower energy states

47 Modern Era Electron Transitions Only Specific wavelengths of light are absorbed and emitted by atoms – you have seen these before Light emitted by atoms is the emission spectra ΔE = Efinal –Einitial E = hν h=Plank’s Constant 4.134×10-15eV·s 6.63×10-34 m2kg/s

48 Modern Era Some Practice! Colors of light are identified by their frequency and/or wavelength Find the frequency of light for transitions 1-3 Find the wavelength of light for transition 3 What does 4 mean? 2 4 3 1

49 Modern Era The 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 time Δx Δp ≥ h Werner Heisenberg Germany

50 Modern Era The New Quantum Model In 1926 Erwin Schrödinger developed an equation that took care of all inconsistencies of Bohr’s model Completely treated electrons as waves (Ψ) Accounted for uncertainty principle This took the electron from existing in defined orbits to living in a “probability cloud” Concentric probability clouds expand out from the nucleus Probability cloud – the area where an electron is likely to be found The 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 Era The Modern (current) Atom We don’t know any electron’s exact location or momentum Heisenberg uncertainty principle We know electrons act like waves Electrons are likely to exist in some areas around a nucleus, and not in other areas We can find probabilities where electrons can be found Erwin Schrödinger Austria

52 Modern Era What does it look like? Likely electron locations are now represented by probability clouds – a way to graph probability in three dimensions Electron Clouds Electron Bubbles The 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 Era Electron Orbitals Bubbles are much easier to draw…

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