The Structure of the Atom

1. The Structure of the Atom Chapter 4 Chemistry Matter and Change

2. Section 4.1 Early Ideas About Matter

3. Review Vocabulary/Ideas • Matter • Theory • Model • Law of Definite Proportions • Law of Multiple Proportions • Law of Conservation of Matter

4. New Vocabulary/Ideas • Dalton’s Atomic Theory

5. Objectives • Compare and contrast atomic models of Democritus, Aristotle and Dalton • Apply the laws of definite proportions, multiple proportions and conservation of mass to Dalton’s atomic theory

6. Our current understanding of atomic structure began with John Dalton in the early 1800s.

7. Early Greek Philosophers • Democritus • First used the term atom • Understood that matter was not infinitely divisible • Could not explain what held atoms together Atom means indivisible!

8. Early Greek Philosophers • Aristotle • Did not believe that empty space existed • Widely believed for 2000 years • Matter consists of fire, water, air and earth

9. Evidence Becomes Available • Law of conservation of mass • Mass is neither created nor destroyed during ordinary chemical reactions

10. More Evidence • Law of definite proportions • The same compound contains elements in the same ratio, regardless of the amount of material • Example: water is H2O, 2 hydrogen for each 1 oxygen

11. More Evidence • Law of multiple proportions • If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers • 14 g of N bond with 16 g of O to form NO • 14 g of N bond with 32 g of O to form NO2

12. Dalton’s Big Idea • All matter is composed of atoms • Atoms of the same element are identical to each other • Atoms cannot be broken down, created or destroyed • Atoms combine together in whole number ratios • Atoms are rearranged in chemical reactions

13. Can You • Compare and contrast atomic models of Democritus, Aristotle and Dalton • Apply the laws of definite proportions, multiple proportions and conservation of mass to Dalton’s atomic theory

14. Homework • Ch 4 Packet ½ sheet 4.1 Theory • Page 1 • Notebook • Page 44-46

15. Section 4.2 Defining the Atom

16. Review Vocabulary/Ideas • Model • Scientific notation • Dalton’s Atomic Theory

17. New Vocabulry/Ideas • Atom • Cathode ray • Electron • Nucleus • Proton • Neutron

18. Objectives • Define atom • Distinguish between the subatomic particles in terms of relative charge, mass and location • Describe experiments conducted by JJ Thomson and Ernest Rutherford in terms of experimental design and conclusions

19. The atom song

20. An atom is made of a nucleus containing protons and neutrons with electrons in orbit around the nucleus

21. What is an Atom? • An indivisible unit of matter • The smallest particle of a substance that retains all of the properties of that substance

22. The Size of an Atom • Diameter range • 1×10-10 m to 5×10-10 m • Mass range • 1.67x10-24g to 3.2x10-22g • It would take 1 billion billion atoms to make a single drop of water • 1 billion billion is 1,000,000,000,000,000,000

23. Previously believed… • Matter can be broken down to atoms, but no further

24. Evidence dispels prior beliefs • Thomson discovers the electron

25. How we know something is there How we know cathode rays normally travel straight

26. How we know there are particles How we know the particles are negatively charged

27. The electron is discovered • JJ Thomson and the cathode ray • Established that there were negative particles within atoms • Established that the negative particles made up very little of the mass of an atom • Inferred that there were positive components to atoms Video Mass of the electron is 9.109 x 10-31 kg

28. “Plum Pudding” • Used to describe Thomson’s view of the atom • Negative particles are suspended in a positive background • (modern: think mint chip ice cream)

29. The nucleus is discovered • The experimental set-up

30. The nucleus is discovered • What was expected to happen • All alpha particles would pass through the atom unimpeded α particles

31. The nucleus is discovered • What did happen • Most alpha particles passed through the atom unimpeded • Some bounced back α particles

32. Explaining the results • Occasionally the α-particles were hitting something relatively large and solid Video

33. The Nucleus is Discovered • Ernest Rutherford and the Gold Foil • Dispelled the Plum Pudding model • Established that most of the interior of an atom is empty space • The nucleus is a very small, very dense part of the atom • A nucleus the size of a small dot (.) would have a mass equivalent to 70 automobiles! • There are positively charged particles within the nucleus

34. Try it Yourself! • Can you figure out the shape of the target?

35. Try it Yourself! • Can you figure out the shape of the target?

36. Neutrons Finally Discovered • James Chadwick • Discovered the neutron • Explained the mass of the nucleus • Studied under Rutherford • Studied radioactivity

38. Subatomic Particles

39. Can you compare and contrast? Found in nucleus Have a charge Mass number =1 Make up atoms Different members of the same element may vary in number

40. Can you • Define atom • Distinguish between the subatomic particles in terms of relative charge, mass and location • Describe experiments conducted by JJ Thomson and Ernest Rutherford in terms of experimental design and conclusions

41. Section 4.3 How Atoms Differ

42. Review Vocabulary/Ideas • Periodic table • Protons • Neutrons • Electrons • Dalton’s atomic theory

43. New Vocabulary/Ideas • Atomic number • Isotope • Mass number • Atomic mass • Average atomic mass • Atomic mass unit (amu) • Weighted average

44. Objectives • Explain the role of atomic number in determining the identity of an atom • Define an isotope • Explain why atomic masses are not whole numbers • Calculate the number of electrons, protons, and neutrons in an atom given its mass number and atomic number (or identity)

45. The number of protons defines the identity of the atom

46. How do we describe an atom of an element? • Nuclide notation • Periodic table notation

48. How do we describe an atom of an element? Protons • Atomic number (Z) • Number of protons • NEVER changes for a given element • Defines the identity and characteristics of the atom • If it is carbon it has 6 protons • If it has 6 protons it is carbon • A hydrogen atom A carbon atom A gold atom • (1 proton) (6 protons) (79 protons)

49. How do we describe an atom of an element? • Electrons • For atoms, the number of electrons is equal to the number of protons (the atomic number) • They will differ in ions (later in semester)

50. How do we describe an atom of an element? • Neutrons • Atomic mass or Mass number (A) • Number of protons + number of neutrons • May change for a given element (isotopes)