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THE DEVELOPMENT OF ATOMIC THEORY Chemistry Rules!.

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1 THE DEVELOPMENT OF ATOMIC THEORY Chemistry Rules!

2 A time when logic ruled the land… The Philosophical Era (Circa 500~300BCE)

3 Philosophical Era (Ancient Greece) o Two ancient Greeks stand out in the advancement of chemistry. o Their ideas were purely based on logic, without experimental support (as was common in that time)

4 Democritus ( BCE) o The most well-known proponent of the idea that matter was made of small, indivisible particles o Called the small particles atomos meaning that which cannot be divided o Believed properties of matter came from the properties of the atomos

5 Aristotle ( BCE) o Famous philosopher of the ancient Greeks o Believed matter was comprised of four elements o Earth, Air, Fire, Water o These elements had a total of four properties o Dry, Moist, Hot, Cold o People liked him – so this idea stayed

6 The Dark Ages of Chemistry where early chemists had to work in secret and encode their findings for fear of persecution Alchemical Era (300 BCE ~ 1400CE)

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

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

9 Elements in Alchemy o Alchemists studied many different materials, and their properties, in order to find a way to turn lead into gold and achieve immortality

10 Alchemy had to be discussed in secret so that its students could avoid persecution Alchemical symbols for various materials

11 Alchemists Persecution o Alchemy was tied to witchcraft and druids o it was perceived as heresy by the catholic church o Practitioners had to hide their trade or hobby o Information was passed in code o Coded messages were sent between friends o Symbols were used to avoid readable words o The growth of Chemistry was stunted by the oppression endured during this era (No such problems in the Far East –Hence gunpowder)

12 The printing press heralds the widespread transfer and acquisition of knowledge The Classical Era (1400CE – 1887CE)

13 Foundations o Robert Boyle departs from Aristotle (1661) o Suggested in A Skeptical Chymist a substance was not an element if it was made of more than one component o Antoine Lavoisier ( ) o Accepted Boyles idea of elements o Developed the concept of compounds o Determined Law of Conservation of Mass o Law: There is no change in mass due to chemical reactions o Discovered Oxygen o Recognized Hydrogen as an element

14 Foundations (continued) o Joseph Proust (1790s) o Determined the Law of Definite Proportions o Elements combine in definite mass ratios to form compounds Robert Boyle Irish Antoine Lavoisier (and wife) French Joseph Proust French

15 John Dalton [really famous] ( ) o Dalton returns to Democritus ideas in 1803 with four postulates I. All matter is made up of tiny particles called atoms II. All atoms of a given element are identical to one another and different from atoms of other elements III. 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. IV. 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) o Joseph Gay-Lussac ( ) o 2L hydrogen (g) + 1L Oxygen (g) 2L Water Vapor (g) o Experimental findings disagreed with some of Daltons beliefs o Amadeo Avogadro ( ) o Suggested Hydrogen and Oxygen are diatomic molecules o This solved the riddle over Gay-Lussacs experimental results Joseph Gay-Lussac French Amadeo Avogadro Italian lawyer

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

18 Avogadros Number

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

20 Here is a black and white copy of the manuscript, and an English textbook version Mendeleevs table quickly became famous

21 **Dont Forget Newton!!! ( ) o Isaac Newton was very important to science o He is most remembered for his contributions to physics, including gravity and much work in optics (light) o He was the first person to divide white light into its parts o Splitting light into parts lead to many interesting discoveries

22 The relatively quick discovery of things smaller than the once indivisible atom The Subatomic Era (1897CE – 1932CE)

23 Its Electric! o Electricity was studied throughout the classical era o Ben Franklins kite in a thunderstorm (1752) o Electricity could flow through gasses (atmosphere)

24 Cathode Ray Tubes o Glass chambers used to study electricity in gasses o Crooke observed glowing rays emitted from the cathode o Glowing rays were observed in all gasses, and even gasless set-ups

25 J.J. Thompson English (1897) o Subjected cathode rays to magnetic fields o Using three different arrangements of CRTs he was able to determine that the Cathode rays… o Were streams of negatively charged particles o Those particles had very low mass-to-charge ratios o The observed mass-to-charge ratio was over one thousand times smaller than that of hydrogen ions o The CRT particles had to be much lighter than hydrogen and/or very highly charged

26 Robert Millikan American (1909) o Thompson needed to know either the mass or the charge of his negative particles to describe them o Millikans oil drop let him find that the charge on objects is always some multiple of 1.60× C o He proposed this as the basic increment of charge o Applying this charge to Thompsons particles, he found the mass to be much less than any atom

27 Plumb Pudding Model (1904) o With the combined work of Thompson and Millikan the first subatomic particle was established! o Electrons – one part of an atom with one negative fundamental increment of electrical charge o Since whole atoms were known to be electrically neutral, Thompson developed the plumb pudding model of the atom Negatively (-) Charged electrons Positively (+) charged majority

28 Ernest Rutherford New Zealander (1910) o Rutherford worked with radiation and had heard of Thompsons plumb pudding model o He wanted to use radiation to prove Thompsons model o 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 Ernest Rutherford New Zealand Marie Curie Polish/ French

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

30 The Second Subatomic o After more realizations and experiments the second subatomic particle was formally named (1911) o Through more Nuclear physics Rutherford determined all atomic nuclei were made up of hydrogen nuclei o Hydrogen nuclei are deemed Protons o Antonius van den Broek suggested elements on the periodic table are in order by their increasing number of protons, not Mendeleevs atomic masses o Proton: The massive subatomic particle, within the nucleus of an atom, with a single positive charge

31 The Planetary Model (1911) o Earnest Rutherford took his idea of a nucleus, and the known electrons, to construct a new atomic model o There is a compact nucleus o The nucleus, made of nucleons, is the location of positive charge in the atom o The charge of the nucleus might be proportional to its mass o The orbit of the electrons kept them from falling directly into the nucleus, just like planetary motion The Rutherford Model or The Planetary Model

32 The Third Subatomic (1932) o Electrons and Protons were identified as particles, but these alone could not fully describe atoms o The charge-to-mass ratio of atoms was off without another addition o James Chadwick studied an unnamed form of radiation– he found it to be electrically neutral and about the mass of a proton o Including these particles in the nucleus of the atom solved all discrepancies that were previously observed James Chadwick English

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

34 Atomic Variance An atoms 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 ElectronsProtons IsotopesNeutrons

35 The Quark Era starts in 1964, but that advance can be regarded as outside the realm of chemistry – instead a part of nuclear physics The Modern Era (1900CE – Present) Chapter 5 in your book! Read pages

36 It all begins… (1900) o Scientists believed that we had answered all major questions- only leaving a few items to finish o Max Plank was commissioned to build a better light bulb o He wanted to answer questions about black body radiation o He reluctantly used statistics to solve questions (he was very conservative) o December 14, 1900 Max Plank German, Physicist

37 Statistics in Science o Most science uses regular math (ex: F=ma) o This era starts to deviate from tradition… o The second law of thermodynamics (Boltzmann) o All systems move toward a less organized state o Plank knew about Boltzmanns ideas –but disproved of deviation from tradition o Plank reluctantly adopted statistics to best explain experimental findings, although he didnt want to be progressive o Einstein interpreted Planks use of statistics to start Quantum theory

38 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 h ν Δ E = energy transferred n = integer multiple ν = frequency of light h = Plank constant (4.134× eV·s ) Δ E = nh ν

39 Photon – light packets o 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

40 λ=h/p …or(λ=h/mv) o Wavelength = Planks constant / momentum Wavelength – wave property Planks constant – a fundamental constant × m 2 kg / s Momentum – a mechanical property Momentum = mass × velocity (p=mv) o Find the wavelength of lots of things!

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

42 Bohrs Planetary Model of the Atom o integrated all known information into a new, mathematically based, model of the atom o He kept electrons in orbits around the nucleus o Only allowed certain specific electron orbits for each atom o Electron transitions between energy levels (orbits) could only be jumps – nothing could be in between these energy levels (like steps on stairs) Niels Bohr Danish Physicist

43 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

44 Bohr Energy levels Electrons can only travel in specific energy levels n=1 n=2 n=3 E = The actual energy of the given energy level Z = the nuclear charge (number of protons) This linked the properties of atoms with the observations of emission spectrum E=-13.6eV Z2n2Z2n2

45 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

46 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 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 Δ E = E final –E initial E = h ν h=Planks Constant 4.134× eV·s 6.63× m 2 kg/s

48 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?

49 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 Bohrs, stated: It is impossible to know the absolutely exact position and momentum of anything at the same time Δx Δp h4πh4π Werner Heisenberg Germany

50 The New Quantum Model o In 1926 Erwin Schrödinger developed an equation that took care of all inconsistencies of Bohrs model o Completely treated electrons as waves ( Ψ) o Accounted for uncertainty principle o This took the electron from existing in defined orbits to living in a probability cloud o Concentric probability clouds expand out from the nucleus o Probability cloud – the area where an electron is likely to be found

51 The Modern (current) Atom We dont know any electrons 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 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

53 Electron Orbitals


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