2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Table of Contents Chapter 3 Atoms: The Building Blocks of Matter Section 1 The Atom: From Philosophical Idea to Scientific Theory Section 2 The Structure of the Atom Section 3 Counting Atoms

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Atom: From Philosophical Idea to Scientific Theory Foundations of Atomic Theory Greeks- Democritus - atomos- “indivisible” Ideas based on opinion/thoughts Chapter 3

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Foundations of Atomic Theory 1790’s- quantitative analysis of chemical reactions Several Laws that resulted from experimentation: Law of Conservation of Mass Law of Definite Proportions Law of Multiple Proportions

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Conservation of Mass- mass is neither created nor destroyed in ordinary chemical reactions. Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Definite Proportions A chemical compound always has the same mass ratio of elements Example: SiO 2 silicon dioxide (sand) 46.74% silicon 53.26 % oxygen Mass of desired elementX 100 Total mass of compound

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of multiple proportions: The same two elements may combine in different whole number ratios- will give two different compounds Section 1 The Atom: From Philosophical Idea to Scientific Theory Chapter 3

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Atom: From Philosophical Idea to Scientific Theory Dalton’s Atomic Theory 1808- based on experimental work- 1. All matter is composed of extremely small particles called atoms. 2. Atoms of a given element are identical. 3. Atoms cannot be subdivided, created, or destroyed. 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged. Chapter 3

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Atom: From Philosophical Idea to Scientific Theory Modern Atomic Theory Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that: Chapter 3 Atoms are divisible into even smaller particles A given element can have atoms with different masses.--- isotopes

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Structure of the Atom The Structure of the Atom An atom is the smallest particle of an element that retains the chemical properties of that element. Chapter 3

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Structure of the Atom Electrons- found by JJ Thomson (1897) –Used cathode ray tube –Negatively charged particles –Mass is small 1/1837 mass of hydrogen atom –Relative mass 0 amu (atomic mass unit)

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Structure of the Atom Cathode ray tube Chapter 3

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Structure of the Atom Discovery of the Electron- J. J. Thomson Cathode Rays and Electrons Chapter 3 Experiments in the late 1800s showed that cathode rays were composed of negatively charged particles. These particles were named electrons. “Plum-pudding” model- think chocolate chip cookie

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Structure of the Atom Protons- found by Ernest Rutherford(1918) –positively charged particles found in nucleus –Relative mass 1 amu (atomic mass unit) –# of protons- identifies element

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Structure of the Atom Neutrons- found by James Chadwick(1932) –neutral charge –particle found in nucleus –Relative mass 1 amu (atomic mass unit)

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Properties of Subatomic Particles Section 2 The Structure of the Atom Chapter 3

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Structure of the Atom Discovery of the Atomic Nucleus More detail of the atom’s structure was provided in 1911 by Ernest Rutherford and his associates Hans Geiger and Ernest Marsden. The results of their gold foil experiment led to the understanding that the atom is mostly empty space with a small, dense, positive region. Rutherford called this positive bundle of matter the nucleus. Chapter 3

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gold Foil Experiment Section 2 The Structure of the Atom Chapter 3

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gold Foil Experiment on the Atomic Level Section 2 The Structure of the Atom Chapter 3

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Models- Visual Overview Dalton Thomson Rutherford Today?????

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Determining the components of an atom Use the periodic table and given information in symbolic form to determine: –Atomic number –Mass number –Numbers of protons, neutrons and electrons –Charge of an ion

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Symbol you will see to represent an element A X Z A – mass number Z – atomic number X- symbol of the element

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Atomic Number Atoms of the same element all have the same number of protons. The atomic number (Z) of an element is the number of protons of each atom of that element. Chapter 3

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Atomic Number Chapter 3

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Mass Number The mass number is the total number of protons and neutrons that make up the nucleus of an isotope. Chapter 3

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Mass Number Chapter 3

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Isotopes Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes. Chapter 3

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Designating Isotopes Hyphen notation: The mass number is written with a hyphen after the name of the element. uranium-235 Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number. Chapter 3

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Sample Problem A How many protons, electrons, and neutrons are there in an atom of chlorine-37? Chapter 3

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Additional Problems Xe-135 ? p ? n ? e 25 Mg +2 ? P ? N ? e Chapter 3

31. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Relative Atomic Masses The standard used to compare units of atomic mass is the carbon-12 atom, which has been arbitrarily assigned a mass of exactly 12 atomic mass units, or 12 amu. One atomic mass unit, or 1 amu, is exactly 1/12 the mass of a carbon-12 atom. The atomic mass of any atom is determined by comparing it with the mass of the carbon-12 atom. Chapter 3

32. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Average Atomic Masses of Elements Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element. Calculating Average Atomic Mass The average atomic mass of an element depends on both the mass and the relative abundance of each of the element’s isotopes. Chapter 3

33. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mass Spectrometer- http://www.chemguide.co.uk/analysis/masspec/masspec.GIF www.alevelchemistry.co.uk/Quizzes/images/mass_spectrometry http://www.chemguide.co.uk/analysis/masspec/masspec.GIF

34. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Average Atomic Masses of Elements, continued Calculating Average Atomic Mass, continued Chapter 3 Copper consists of 69.15% copper-63, which has an atomic mass of 62.929 601 amu, and 30.85% copper- 65, which has an atomic mass of 64.927 794 amu.

35. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Relating Mass to Numbers of Atoms The Mole- “The Chemist’s Dozen” Chapter 3 Avogadro’s number6.02  10 23 –number of particles in exactly one mole of a pure substance. Avogadro’s Number mole (abbreviated mol) Enables small particles to be counted SI unit to describe quantity.

36. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Molar Mass Chapter 3 The molar mass of an element is numerically equal to the atomic mass of the element Molar mass is usually written in units of g/mol. The mass of one mole of a pure substance is called the molar mass of that substance.

37. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Chemists use molar mass as a conversion factor in chemical calculations. Chapter 3 For example, the molar mass of helium is 4.00 g Heor1 mol He 1 mol He4.00 g He Gram/Mole Conversions

38. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mole conversions Molar mass in grams = 1 MOLE = 6.02 X10 23 particles Samples to try moles and grams moles and atoms atoms and grams

39. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Sample Problems- Moles to grams What is the mass of one mole of aluminum? What is the mass of 1 mol of chlorine? Chapter 3

40. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Sample Problem – What is the mass of.455 moles of silver? What is the mass of 2.50 X 10 -4 moles of lead? Chapter 3

41. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Sample Problem- Moles to atoms How many atoms are in 3.45 moles of copper? Chapter 3

42. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Moles to grams How much lead should I mass to get 1.67 moles?

43. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Counting Atoms Atoms to moles How many moles of aluminum do you have with 4.75  10 34 atoms of aluminum? Chapter 3

44. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atoms to grams If I wanted 5.00 X 10 15 atoms of gold, how many grams would I need?