Atomic Structure

1. Atomic Structure Cause of Electrostatics Force & Electricity

2. Atom History • Atom Comes from “atomos” • Democritus first developed the theory of an indivisible part of matter • Survived for almost 2000 years

3. Greek Model • Atoms were spherical particles that are indivisible forms of matter • Water atoms shown below according to Greek model

4. Dalton Model for Atom • Stated “Matter, though divisible in an extreme degree, is nevertheless not infinitely divisible” • Was the first experimental evidence for the atomic theory produced nearly 2000 years earlier • Atoms still thought to be indivisible

5. Daltons Experiments

6. Dalton’s Experiments • First experimental evidence of atomic theory • Held for almost 100 years more as indivisible atoms

7. Thomson Experiment • Studied the cathode rays that are produced when electricity is put in a glass tube • Cathode rays move toward positive charge

8. Thomson Model • Proved atoms must have a negative charge in them • If total charge of an atom is zero then there must be positive charge somewhere • Held for only 15 years

9. Rutherford Experiment • Fired alpha particles at a very thin gold foil • Measured the angle the rays deflected as they passed thru

10. Rutherford Experiment Close Up

11. Rutherford Model • Atoms are made of mostly empty space • Similar to how planets orbit a star

12. Niels Bohr • Worked closely with Rutherford after Rutherford’s famous experiment • Tried to explain line spectrums or electromagnetic waves produced when sealed gas tubes are hooked up to electricity

13. Line Spectrum • Different atoms produce different isolated spectrum

14. Proton-Neutron-Electron Size The Proton and the neutron are roughly equal size with a neutron being slightly bigger. The electron is roughly 1000 X smaller than both

15. Proton-Electron Distance The proton-electron distance is about 100,000 times the diameter of a proton or about 100,000,000 times the diameter of an electron Earth to beyond Pluto

16. Clicker Quiz #1 What did JJ Thomson contribute to the model of the atom? • using experimental evidence to show elements • determining that electrons orbit in distinct levels • proving the the presence of a nucleus and the atoms are made of mostly empty space • proving that a difference in charge is present including quantized negative charge • none of these

17. Clicker Quiz #2 • Who did the following experiment? Measured the deflection of cathode rays across an electric potential. a. Democritus b. Dalton • J.J. Thomson • Rutherford e. Niels Bohr

18. Clicker Quiz #3 Which of the following elements is NOT present in the mixture? a. lithium b. hydrogen • Helium • sodium • more than one element is missing

19. Clicker Quiz #4 You are trying build a scale model of an atom. If you decided that the electron should be the size of a basketball (25 cm) then how big should the proton be? • .25 cm pea • 2.5 cm golf ball • 25 m Planet Hollywood Ball • 250 m Ball one about the size of the RHHS campus • 2,500,000 m ball about ¼ of the Earth

20. Clicker Quiz #5 You are trying build a scale model of an atom. If you decided that the electron should the size of a water tower ball (4 m) then how far apart should the proton an electron be? • Proton in this class Electron on Football field (500 m) • Proton in this class Electron at RHS (5000 m) • Proton in this class Electron in downtown Dallas (32000 m) • Proton in this class Electron Washington D.C. (800,000 m) • Proton in this class Electron on the moon (400,000,000 m)

21. Charge • There are only two types of charges • Positive; number of protons exceed number of electrons • Negative; number of electrons exceed number of protons

22. Charged Objects Charge values are often expressed as +7 or – 2 in Chemistry. Cu2+ These are not really charges but expressions of the number of excess protons or electrons

23. Total Charge • One proton/electron has a charge value of 1.6022 X 10-19 C • The total charge can be calculated using: q = Ne

24. Teacher Example Determine the number of excess electrons in -1 C of charge

25. Example • Determine the charge of a calcium ion

26. Teacher Example • Determine the charge of 65 g of Cu2+

27. Example Determine the mass of nickel that each have one electron removed resulting in a charge of 2.6 C

28. Changing Charge • It is possible to transfer electrons by direct contact between objects • Only electrons are transferred never protons or neutrons

29. Charging by Conduction Requires direct contact between objects of different charges

30. Charging by Friction Use the work done by friction to physically remove electrons. Sometimes not distinguished from conduction

31. Charging by Induction Transferring charge without directly touching another charged object

32. Polarization An object is said to be polarized when the net charge is zero but the charges are divided into positive and negative halves

33. Conductors Mostly metals that contain “free” electrons or electrons in the outer most level that are easily removed Anything that allows electrons to move through with relative ease Gold is an excellent Conductor

34. Law of Conservation of Electric Charge • The total amount of charge in a system must remain the same • If total charge is 0 for a system than two objects can have any charge as long as the total of the two is zero

35. Teacher Example • What will the charge of each be after they are allowed to touch?

36. Clicker Quiz #1 Two spheres of A of +5 and B of -9 are touched and then separated. What should the charge of each be after this? A B • +5 -9 • -9 +5 • +2 +2 • -2 -2 • -4 -4

37. Clicker Quiz #2 A 10 C objects is touched to a -10 C charge object which best describes what happens at the molecular level • Protons move from the 10 C to the -10 C until balanced • Neutrons move from the 10 C to the -10 C until balanced • Electrons move from the -10 C to the 10 C until balanced • All of these occur until balanced • None of the above both objects must be grounded.

38. Clicker Quiz #3 What method of charge transfer is occurs when • Conduction • Induction • Friction • Polarization • All of these

39. Clicker Quiz #4 What is the charge of an object that has 1/1000th of a mole more protons then electron? (Round to the nearest whole number)

40. Clicker Quiz #5 What is the charge of 40 g of doubly ionized sulfur? Round to 2 significant digits

41. Fundamental Law of Static Electricity • Opposite charges Attract • Alike charges repel

42. Example What will the path of the particle be ?

43. Electrostatic Force • Can be calculated using: Fe= kq1q2 r2 Any negative force is an attractive force Any positive force is a repulsive force K = 8.99 X109

44. Teacher Example Which graph best represents the relationship between electrostatic force and distance?

45. Student Example • Determine the force from two 1 C charges separated by a distance of 1 km

46. Teacher Example Determine the distance between two charges of 1.0 X 10^-4 C and –5.0 X 10^-5 C if they are subjected to 1 N of force between them

47. Example If two particles have the same charge and are separated by 10 m resulting in a force of 1 N. What is the value of each charge?

48. Electric Fields • Cause these attractive and repellant force • Always drawn from positive to negative • Cannot draw electric field for two negative particles

49. Parallel Plate Capacitors Two plates that have different charges and each charge is spread equally along the plate

50. Clicker Quiz #1 Replace distance with charge. Which graph best represents the relationship between electrostatic force and charge? A C B D