Review of Atomic Theory

1. Review of Atomic Theory Period 7.

2. Leucippus Pre-Socratic philosopher Born in Abdera, Elea, or Miletusin the 5th Century B.C.

3. Democritus • Lived from 460-370 B.C • Ancient Greek philosopher • His mentor was Leucippus • The two of them worked together on atoms • He was more of a scientists than other Greek philosophers

4. The Atomic Theory of Matter Leucippus and Democritus realized that the world consisted of myriads of indivisible particles, called atoms which were the smallest particles of matter possible Upon further speculation, they came up with the idea that the observable properties of common materials are because of the different shapes of atoms which they contain, or different motions of atoms

5. Aristotle • Lived from 384 to 322 BC • He was a Greek philosopher • A student of Plato and a teacher of Alexander the Great • Had ideas referring to many different subjects

6. Aristotle's Early Theories on the Atom • Aristotle’s Theory of the Elements: A piece of matter could be divided an infinite number of times and one would never find a piece of matter that could be further divided • He believed in the four elements: earth, fire, water, and air • According to him, everything in the world was made up of some combination of these four elements • At this time this was the most popular theory.

7. The Significance of the Atomic Theories The atomic theories that were created at this time were not 100% accurate; however, they provided insight in an area never explored before The central ideas of Leucippus and Democritus have remained unchanged

8. Antoine Lavoisier & The Law of Conservation of Matter By: Jin Shin & Taylor Seeman Born: August 26, 1743 Died: May 8, 1794 “Father of Modern Chemistry”

9. Educational Background • Attended the College Mazarin at the request of his aunt • College Mazarin had an excellent mathematics and science program • Lavoisier was a brilliant student, and earned numerous awards • He conducted his first few experiments individually or while aiding professors.

10. Experiment • Lavoisier burnt phosphorous and sulfur in air and proved the products weighed more than the reactants but the weight gained was lost from the air.

11. Experiment • When you heat a piece of copper metal in air, it comes together with oxygen in the air. If you weigh it, it is found to have a greater mass that the original piece. However, the mass of the oxygen of the air is combined with the mass of copper, the mass of the product is equal to the sum of the masses of the copper and oxygen that were combined.

12. Significance of Concept • Showed that the quantity of matter is the same in the beginning and end of every chemical reaction, though matter may change its state. • Though matter may change form, it can neither be created nor destroyed • Mass of reactants always equal the mass of products

13. Law demonstrates understanding of the properties of movement and energy. It is a fundamental principle of physics. Sources: http://www.iscid.org/encyclopedia/Law_of_Conservation_of_Mass http://www.biographybase.com/biography/Lavoisier_Antoine_Laurent.html Significance of Concept

14. Joseph Proust: Law of Definite Proportions -born in France (1754-1826) -son of a pharmacist -chief apothecary at Saltpetriere Hospital -became the director of Royal Laboratory under Charles IV -laboratory was destroyed by the invasion of Spanish Army by Napoleon so he returned to France By: Simir and Katie

15. Joseph Proust -Lived in poverty before being awarded pension by Louis XVIII -He taught at the Chemistry school at Segovia and the University of Salamanca at Spain -He was the chair of this school and was proposed in 1784 to to train artillery cadets with the latest scientific knowledge -He worked with Antoine Lavosier -He also taught chemistry at Musee, a private school in Paris,

16. Experiment • Proust prepared a copper carbonate compound • He heated it, getting rid of the water and then the carbonic acid, or what was left of the copper oxide • - From the 180 lbs of "copper carbonate" (it was actually carbon dioxide) he took away 10 lbs of water and 46 of the carbon dioxide • - The copper oxide left had 100 lbs of copper and 25 of oxygen

17. Experiment • Decomposition of CuCO3 into Cu, C and O • Proust found that the ratio of the masses of Cu to C to O was always the same no matter what size sample of CuCO3 he started with. • He formed his theory by dividing to find the ratios

18. Example Set of Data

19. Significance • Law of Definite Proportions • Copper carbonate must always be made from the same fixed proportions of copper, carbon, and oxygen • All compounds contain elements in certain definite proportions • Ex) Nitric Oxide- 8:7 oxygen to nitrogen • Ex2) Water- 8:1 oxygen to hydrogen

20. Significance in the Scientific Community • Initially not accepted by all chemists • ie) Claude-Louis Berthollet argued that elements could combine in many different proportions (actually thinking of solutions/mixtures- Proust was thinking of compounds) • Law of Definite Proportions was the basis for John Dalton’s atomic theory and multiple proportions

21. Significance in Scientific Community cont • Proust expanded upon Lavoisier’s Law of Conservation of Mass • Law of Conservation of Mass-mass of reactants was always equal to mass of products (matter cannot be created or destroyed) • Proust measured each individual substance instead of the total mass for reactants and products

22. John Dalton Early Life • From Cumberland, England • Birth date is unknown • Family were Quakers • Worked in the fields and in the family cloth shop • Relatively poor • Did not get formal education • Did get basic lessons in reading, writing, and arithmetic

23. John Dalton Adult Life • Dalton and his brother ran a school in Kendal • Dalton recorded the weather patterns each day (for his entire life) in a journal • Originally wanted to be a physician, decided on scientist instead • Tutored students at Manchester University

24. Dalton’s Law of Multiple Proportions If 2 elements form multiple compounds, the ratios of the masses of the second element combining with a fixed mass of the first element will be in ratios of small whole numbers

25. Dalton’s Law of Multiple Proportions For Example Elements Y and Z The weight of Element Z, when combined with the fixed weight of element Y, will compute to a ratio of small integral numbers (2:1, 3:1, etc.) OR Carbon + Oxygen = CO, CO2, but not CO1.3 Y Z

26. Importance of Dalton’s Law of Multiple Proportions • One of the fundamental laws of stoichiometry • Basis for other Atomic Theories • Law of Conservation of Mass • Law of Definite Proportions

27. Dalton’s Modern Atomic Theory • All matter is made of atoms • Atoms are invisible and indestructible • All atoms of a given element are identical in mass and properties • Compounds are formed by a combinations of two or more different kinds of atoms • A chemical reaction is a rearrangement of atoms

28. The Discovery • Dalton studied gases • Discovered the partial pressures of gases • Lead to formulation of working theory of the atom • *Noticed that certain gases maintained the same ratios of mixture regardless of amount • Realized that Ratios remain the same because they were consistent down to the smallest particle or atom

29. Significance of Dalton’s Atomic Theory • First understanding of the atom • Prior to, it was an abstract philosophical concept • The essence of Dalton’s theory remains valid • Led to great expansion of theoretical thought in chemistry

30. JJ Thomson -Discovered the electron and also invented the mass spectrometer -Interested in sciences as a child and later on his life showed a large interest in atomic structure -Graduated and taught at Trinity College after a brief stay at Owens College -Was an author of many non-fiction science books

31. Personal Life -Born in Cheetham Hill, Manchester on Decemeber 18, 1856 -Full name Sir Joseph John Thomson -Father died when he was only 16 -In 1890 he married Rose Elizabeth -He had one son named Sir George Paget Thomson

32. The Discovery -A century ago discovered the electron while using a Cathode Ray Tube -Cathode Ray Tube is a glass tube that has wiring attached to its two sides. -The air is taken out and in order to try and form a vacuum. -An electric charge goes from one end to the other and produces a glow that looks fluorescent. -A cathode ray or electron gun is attached to the glass contraption

33. The Experiment -Used his Cathode Ray Tube made a unique tube to probe that the rays shot in had a negative charge. -Almost perfect vacuum and he put the fluorescent layer on a specific side. - Had an electric plate, this gave a positive charged electrode to the negative cathode. The ray would be deflected. -Shot a ray got deflected by the opposite positive charge. This showed that the ray was made up of charged, negatively particles.

34. The Third Experiment -Figured out that the charge to mass ratio could have been very large or extremely small -Chose correctly that they were very small

35. Significance -Later Devices, helps with electronic devices, making impulses so a screen can run and one can see a display. -Cathode-Ray Tube can produce an image on a screen with electrical impulses. -It can primarily help with TV screens and computer screens. -Disproved Plum-Pudding theory

36. Robert Andrews Millikan -born in 1868 in Illinois -grew up in Iowa -worked on Oil Drop Experiment in University of Chicago (professor) -1923: Nobel Prize for Physics

37. The Discovery • At University of Chicago • Performed a series of experiments • Wanted to find the charge of an election • Worked off Thomson’s experiments

39. The Experiment • The atomizer produces fine oil droplets • Oil droplets fall through a hole in the first chamber as a stream of tiny droplets • X-rays negatively charge the oil droplets • An applied voltage on two plates surrounding the oil drops creates an electric field. The electric force pull some drop upward. • The rate at which the oil droplets are falling and rising between the two charged plates is measured through the microscope.

40. The Experiment • Some oil droplets fell, and some did not • This depended on the forces acting upon it: electric force, gravitational force, and air resistance • He found… • 1. When a large electric field is applied, but the electric force on the droplet is larger, then the gravitation force acts in the opposite direction: it moves upward • 2. Net force of a droplet=sum of the gravitational force, the air resistance, and electrical force • V1=k(Eq-mq)

41. The Experiment • In simpler terms… • When there was no voltage applied, the droplet would fall down to the bottom • Voltage applied, droplets with negative charge drop more slowly, stop altogether, or even go up (depending on the voltage given) • Charges of the droplets were all multiples of the smallest value • e-=1.6 x 10 to the -19 coulombs

42. Significance of Experiment • Calculated charge of electron • Showed that charge on electron was smallest possible amount of charge • Total amount of electric charge must always be an integer multiple of this electric charge

43. Significance of Experiment • Now that the charge of an electron is discovered, further advancements in science can be made on the atom • An atom is the basic unit of an element • With the discovery of an electron, we can find out more on the states of substances, elements, etc. • Without him, chemistry would not have advanced much

44. Earnest Rutherford As well as Marsden and Geiger and their gold foil experiment

45. Background Info • Ernest Rutherford, 1st Baron Rutherford of Nelson was a British-New Zealand chemist and physicist. In his early work he discovered the concept of radioactive half and also differentiated and named alpha and beta radiation. He was awarded the Nobel Prize in Chemistry in 1908 "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances”.

46. Before his Experiment Before his experiment people though that the particles in an atom were randomly arranged according to the plum pudding model. See diagram below.

47. Hypothesis Rutherford thought that if the plum pudding model was correct then a beam of alpha particles would go though matter with very little deflection. See diagram below.

48. Experiment Rutherford’s experiment consisted of a block of radium to generate alpha particles, gold foil for the particles to pass trough and a florescent screen that he could use to determine where the alpha particles ended up. See diagram below.

49. Conclusions The Gold Foil experiment showed that the plum pudding model of the atom was not accurate. This is because the experiment showed how there had to be a piece of the atom with a large mass in the center of the atom. The realization that things were not just loosely "hanging out" around an atom but instead are arranged in a specific way around a center led him to discover the Atomic Nucleus. See diagram below

50. More Conclusions Without this discovery, much of what we know about atoms would not be possible. If not for the discovery of the nucleus, we could not know about the important parts that it consists of (protons and neutrons). Also, the periodic table of elements that we all know so well (from intense memorization for Chemistry tests), the elements would not be ordered the same way, because Atomic number is the number of protons in the nucleus of an atom. Also, we can also identify different atoms by mass number. This is the number of protons and neutrons added together in the nucleus. All these things, and many more, that are the basis of our knowledge of atoms would not be possible without the information from Rutherford's Gold Foil Experiment.