1. Free Powerpoint Templates Page 1 History of the Atom (Chapter 4) Why Study Atoms? First ideas of the Atom, The Greeks Robert Boyle, Joseph Proust, and Antoine Lavoisier Dalton’s Atomic Theory Thomson’s Model Rutherford’s Atomic Theory

2. Free Powerpoint Templates Page 2 There is a Problem Atoms are extremely small You can not see them. Because of this, most evidence of their existence is through indirect evidence.

3. Free Powerpoint Templates Page 3 But That Doesn’t Stop Science However, the idea that atoms exist is one of the most strongly supported of all scientific theories. Scientists and engineers spend millions of man- hours each year studying atomic processes Governments and Companies spend 100’s of billions of dollars each year studying Atomic processes

4. Free Powerpoint Templates Page 4 Why Study About Atoms? Everything made of matter is made of atoms. To understand atoms is necessary to understand most of science and the world around us. Almost all new technologies requires the understanding of atoms or their subatomic parts.

5. Free Powerpoint Templates Page 5 Think About The more you know about atoms the more you know about yourself.The more you know about atoms the more you know about yourself. The more you know about atoms the more you know about the world around you.The more you know about atoms the more you know about the world around you.

6. Free Powerpoint Templates Page 6 Who Thought of Atoms First? The Ancient Greeks Democritus and Leucippus Greek philosophers (~400BC) reasoned you couldn't grind something forever into smaller pieces. Would be no shape to objects Believed there must be an ultimate small particle things were made of Called the “Atomos” for indivisible

7. Free Powerpoint Templates Page 7 Leucippus is named by most sources as the originator of the theory that the universe consists of two different elements, which he called ‘the full’ or ‘solid,’ and ‘the empty’ or ‘void’. Both the void and the solid atoms within it are thought to be infinite, and between them to constitute the elements of everything. To Democritus, atoms were completely solid, homogeneous, indestructible objects.

8. Free Powerpoint Templates Page 8 Democritus – He said that there was only so many times that something could be broken down into smaller pieces than the previous one. It had to end at some point with the smallest thing you could get, the atom. He was the founder of the atomic hypothesis. He thought that everything was formed up of atoms like the objects itself, such as all trees were lots of small trees put together.

9. Free Powerpoint Templates Page 9 Thales (around 600 B.C.) There was someone earlier – kind of Thales of Miletus discovered that after rubbing a piece of amber with fur it would attract other light objects. He suggested that this force came from inside the amber but did not completely develop his idea and connect it with the atom Thought everything was made of one element, water..

10. Free Powerpoint Templates Page 10 Aristotle (384-322 B.C.) Thought all substances were built up of four elements –Earth (cool & heavy) –air (light) –water (wet) –fire (hot) Blend these in different proportions to get all substances

11. Free Powerpoint Templates Page 11 Who Was Right? Greek society was slave based It was beneath the Famous to work with their hands Typically didn't experiment Greeks settled disagreements by argument & logic Aristotle was more famous He won His ideas carried through middle ages.

12. Free Powerpoint Templates Page 12 Aristotle's Ideas about the elements was accepted through the dark ages. But the idea of the “atomos” was largely forgotten.Aristotle's Ideas about the elements was accepted through the dark ages. But the idea of the “atomos” was largely forgotten. However, alchemists by the end of the dark ages realized there must be more than 4 elements silvergoldironcopperi.e., silver, gold, iron, copper, carbon, etc. It was time for a change.

13. Robert Boyle (1600’s) 1 st true “chemist”1 st true “chemist” First to... –develop modern concepts of element and compound; –to distinguish between acids, bases, and neutral substances; –conduct and publish experiments along the lines of the scientific method. –Discovered a relationship between pressure and volume (Boyle’s Law)

14. Antoine Lavoisier (1743-1794) He burnt phosphorus and sulfur in air, and proved that the products weighed more than he original. Nevertheless, the weight gained was lost from the air. Thus he established the ”Law of Conservation of Mass”. Matter cannot be created or destroyed

15. Joseph Proust (1754 - 1826) Found that a given compound always contains exactly the same proportion of elements by mass “Law of Definite Proportion” i.e., if one sample of water breaks down into 2 grams of hydrogen and 16 grams of water, then twice the amount of water would contain 4 grams of hydrogen and 32 grams of water. The proportion of hydrogen to oxygen is "definite" or fixed.

16. Free Powerpoint Templates Page 16 Dalton’s Atomic Theory The Father of Modern Chemistry (born 1766) Reintroduced the Idea of the atom along with 4 rules concerning atoms, compounds and chemical reactions. 1)All matter is made of atoms. - Atoms are indivisible and indestructible. - can not be created or destroyed

17. Free Powerpoint Templates Page 17 Dalton’s Atomic Theory (cont.) 2) All atoms of a given element are identical in mass and properties

18. Free Powerpoint Templates Page 18 Dalton’s Atomic Theory (cont.) A compound made of 3 elements. Which ones? - Hydrogen - Oxygen - Carbon 3) Compounds are formed by a combination of two or more different kinds of atoms.

19. Free Powerpoint Templates Page 19 Dalton’s Atomic Theory (cont.) 4) A chemical reaction is a rearrangement of atoms.4) A chemical reaction is a rearrangement of atoms. Weee got ya carbon Hay, we have the oxygen

20. Free Powerpoint Templates Page 20 Thomson’s Model of the Atom (1897) Discovered the atom was made of smaller parts. How did he do it? Thomson used a CRT (Cathode Ray Tube)Thomson used a CRT (Cathode Ray Tube)

21. Free Powerpoint Templates Page 21 The CRT (Cathode Ray Tube) The green beam emitted by the cathodes atoms could be deflected by a charged plate Why? The beam must be made of charged particles. Like charges ________, Unlike ________ Beam attracted to positive plate so what charge is it? Negative repelattract

22. Free Powerpoint Templates Page 22 Moving the Electron Beam ● Can use magnets or charged metal plates to move around the beam. ● Means the beam is charged.

23. Free Powerpoint Templates Page 23 Plum pudding model of atom : electrons embedded in positive charged gel

24. Free Powerpoint Templates Page 24 Plum Pudding Model

25. Is there a Problem with Thomson’s Model???? If opposite charges attract and likes repel. If opposite charges attract and likes repel. Why don’t the electrons get repelled to the surface of the gel??? They would end up like sprinkles on top of a cupcake. Not inside it. ?

26. Robert Millikan In 1911, Robert Millikan devised one of the classic experiments in atomic physics and chemistry, “oil-drop experiment”. the “oil-drop experiment”. He constructed a chamber with a graduated view lens. The chamber had oppositely-charged plates. He used an atomizer to spray tiny oil drops between the plates. chargemass By adjusting the charge on the plates until a drop was suspended, he determined the charge and mass of the electron.

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28. Free Powerpoint Templates Page 28 The Solution Rutherford’s Atomic model In 1911 Ernest Rutherford determined the true nature of atom. New Zealand born English physicist. Believed in the plum pudding model of the atom. (worked for Thomson at one point)

29. Free Powerpoint Templates Page 29 Shot things at Atoms alpha particlesHis experiment used alpha particles as atomic bullets. Wanted to see what happened. Did they -Go through -Bounce -Break things? Side view

30. Free Powerpoint Templates Page 30 Rutherford’s experiment Wanted to see how big atoms were Used radioactivity Alpha particles - positively charged pieces given off by uranium alpha particlesHis experiment used alpha particles as atomic bullets. gold foilShot them at gold foil which can be made a few atoms thick

31. Free Powerpoint Templates Page 31 What did he do? Rutherford beamed alpha particles through gold foil Detected them as flashes of light on a florescent screen The gold foil was only –-0.00004 centimeter thick. (1/400,000 th ) –a few hundred atoms thick. Top View

32. Lead block Uranium Gold Foil Florescent Screen

33. Free Powerpoint Templates Page 33 He Expected The alpha particles to pass through without changing direction very much Because The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles

34. Free Powerpoint Templates Page 34 What he expected

35. Because

36. Because, he thought the mass was evenly distributed in the atom

38. Free Powerpoint Templates Page 38 What he observed

39. Free Powerpoint Templates Page 39 Most alpha particles passed straight through the gold foil A few were scattered Some even bounced back He observed the following:

40. How he explained it + Atom is mostly empty Small dense, positive piece at centerSmall dense, positive piece at center Alpha particles are deflected by it if they get close enough

41. +

42. Free Powerpoint Templates Page 42 Inferred Only a very small, heavy, positively charged center could cause these results. Reasoned there must be a very small hard center to the atom. Demonstrated the atom had a nucleus.

43. Free Powerpoint Templates Page 43 The Nucleus Tiny center of the atom, 1/10,000 th the size of the atom. The nucleus positively charged. Contains almost all the mass of the atom. Electrons (negatively charge) circulate at a distance around the nucleus.

44. Free Powerpoint Templates Page 44 To Summarize By the early 1900’s scientists knew that the atom consisted of a small dense nucleus with little electrons in orbit around the nucleus But...They didn’t know how the electrons were arranged

45. Free Powerpoint Templates Page 45 Where are the Electrons? In the Electron Cloud The electrons are held in orbit by their attraction to the protons Due to the electromagnetic force But, this force also makes electrons repel each other -- 00 - +

46. Free Powerpoint Templates Page 46 What does this mean? This force causes the “electron Cloud” to be 10,000 times larger than the nucleus Thus, the “electron cloud” is mostly empty space.

47. Free Powerpoint Templates Page 47 Modern View The atom is mostly empty space Two regions Nucleus Protons (+) Neutrons (o) Electron cloud region where you might find the electrons (-)

48. Free Powerpoint Templates Page 48 Now know Atoms Are Made of Smaller “Subatomic” Parts

49. Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ n0n0 +1 0 1/1840 1 1 9.11 x 10 -28 1.67 x 10 -24

50. What Makes The Atoms of Different Elements Different From Each Other? The number of electrons, protons and neutrons they contain. The atoms of each element contain a unique combination of each of these parts.

51. Free Powerpoint Templates Page 51 How do you ID the Element the Atom Represents? By the number of protons in the atom or atomic number. The atoms of each element are unique.

52. Free Powerpoint Templates Page 52 For Each Element There Is a Unique Atom

53. Free Powerpoint Templates Page 53 It is All Recorded on the Periodic Table

54. Free Powerpoint Templates Page 54 Atomic number The number of protons

55. Free Powerpoint Templates Page 55 Atomic Mass The number of protons The number of protons+ Neutrons in an atom (the mass of the nucleus)

56. Free Powerpoint Templates Page 56 Figuring Parts # Protons = Atomic Number # Electrons = Protons, unless the atom is an ion (ionized). # Neutrons = Atomic Mass - Atomic Number (rounded) The #neutrons and #protons do not have to equal

57. Free Powerpoint Templates Page 57 Isotope Atoms with the same number of protons but a different number of neutrons They are radioactive atoms (will decay) Unstable - nucleus falls apart

58. Free Powerpoint Templates Page 58 Ion Atoms with the same number of protons and neutrons but a different number of electrons Are “Ionized”

59. Free Powerpoint Templates Page 59 Zero Charge (neutral) is Normal Atoms are normally neutral –charges add up to zero (0). Thus, # protons (+) = # electrons (-) unless ionized

60. Free Powerpoint Templates Page 60 Atoms which have a charge, have been ionized. By adding or removing electrons. A superscripted number is used to show the charge on the ion. i.e.)Ca +2 and F -1

61. Free Powerpoint Templates Page 61 The Anion – a Negative Ion If add electron(s) the atom becomes more negative. Called an Anion. i.e.) Carbon becoming an Anion C + 2e - → C -2 (anion)

62. Free Powerpoint Templates Page 62 The Cation – a Positive Ion If remove electron(s) the atom becomes more positive. Called a Cation. i.e., Sodium becomes an Cation Na +2 if 2 electrons are removed.

63. Free Powerpoint Templates Page 63 What About Protons? Protons are never removed or added to ionize an atom. They are stuck in the nucleus –can’t be moved –strong force holds them Electrons are easy to remove or add –located on the outside of the atom.