1. Lecture Presentation Chapter 2 Atoms, Molecules, and Ions Dr. Subhash C. Goel South GA State College Douglas, GA © 2012 Pearson Education, Inc.

3. Copyright © Cengage Learning. All rights reserved.2 | 3 Law of Multiple Proportions When two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in small, whole-number ratios.

5. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place.

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7. Copyright © Cengage Learning. All rights reserved.2 | 7 Structure of the Atom The atom is composed of two parts: Nucleus Central core Positively charged Contains most of the atom’s mass Electrons Very light Negatively charged Exist in the region around the nucleus

8. Copyright © Cengage Learning. All rights reserved.2 | 8 Discovery of the Electron J. J. Thomson used an apparatus similar to the one shown on the next slide, a cathode ray tube. He discovered that the particles that make up the cathode ray are negative and are part of all matter. This finding is illustrated on the following slides. As a result, Thomson concluded that atoms are not indivisible, as Dalton had postulated.

9. Copyright © Cengage Learning. All rights reserved.2 | 9 Cathode Ray Tube

10. Copyright © Cengage Learning. All rights reserved.2 | 10 Cathode rays are attracted to the positive end of the magnet and repelled by the negative end.

11. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. The Electron Thomson measured the charge/mass ratio of the electron to be 1.76  10 8 coulombs/gram (C/g). Robert Millikan calculated the charge on the electron. He determined the charge on various drops of oil and found the smallest increment in charge—that is, the charge on the electron. This is illustrated on the next slide.

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13. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Radioactivity Radioactivity is the spontaneous emission of radiation by an atom. It was first observed by Henri Becquerel. Marie and Pierre Curie also studied it.

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15. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc.

16. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. The Atom, circa 1900 The prevailing theory was that of the “plum pudding” model, put forward by Thomson. It featured a positive sphere of matter with negative electrons imbedded in it.

17. 1.atoms positive charge is concentrated in the nucleus 2.proton (p) has opposite (+) charge of electron (-) 3.mass of p is 1840 x mass of e - (1.67 x 10 -24 g)  particle velocity ~ 1.4 x 10 7 m/s (~5% speed of light) (1908 Nobel Prize in Chemistry) 2.2

18. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. The Nuclear Atom Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom. Most of the volume of the atom is empty space.

19. Chadwick’s Experiment (1932) (1935 Noble Prize in Physics) H atoms - 1 p; He atoms - 2 p mass He/mass H should = 2 measured mass He/mass H = 4  + 9 Be 1 n + 12 C + energy neutron (n) is neutral (charge = 0) n mass ~ p mass = 1.67 x 10 -24 g 2.2

20. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Subatomic Particles Protons and electrons are the only particles that have a charge. Protons and neutrons have essentially the same mass. The mass of an electron is so small we ignore it.

21. Atoms, Molecules, and Ions Exercise 1.How many protons, neutrons, and electrons are in (a) an atom of 197 Au, (b) an atom of strontium-90? 2.How many protons, neutrons, and electrons are in (a) a 138 Ba atom, (b) an atom of phosphorus-31? © 2012 Pearson Education, Inc.

22. Copyright © Cengage Learning. All rights reserved.2 | 22 Atomic Symbol An atomic symbol is a one- or two-letter notation used to represent an atom corresponding to a particular element. The first letter must be UPPERCASE. The second letter, when present, must be lowercase. Symbols come from the element name; several names come from Latin.

23. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Symbols of Elements All atoms of the same element have the same number of protons, which is called the atomic number, Z.

24. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Symbols of Elements The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

25. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Isotopes Isotopes are atoms of the same element with different masses. Isotopes have different numbers of neutrons.

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27. 6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons Do You Understand Isotopes? 2.3 How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ?

28. Exercise 1.Magnesium has three isotopes with mass numbers 24, 25, and 26. (a) Write the complete chemical symbol (superscript and subscript) for each. (b) How many neutrons are in an atom of each isotope? 2.Give the complete chemical symbol for the atom that contains 82 protons, 82 electrons, and 126 neutrons.

29. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Atomic Mass Atomic and molecular masses can be measured with great accuracy using a mass spectrometer.

30. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Average Mass Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. Average mass is calculated from the isotopes of an element weighted by their relative abundances.

31. Atoms, Molecules, and Ions Exercise Naturally occurring chlorine is 75.78% 35 Cl (atomic mass 34.969 amu) and 24.22% 37 Cl (atomic mass 36.966 amu). Calculate the atomic weight of chlorine. © 2012 Pearson Education, Inc.

32. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Periodic Table The periodic table is a systematic catalog of the elements. Elements are arranged in order of atomic number.

33. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Periodic Table The rows on the periodic chart are periods. Columns are groups. Elements in the same group have similar chemical properties.

34. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.

35. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Groups These five groups are known by their names.

36. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Periodic Table Nonmetals are on the right side of the periodic table (with the exception of H). Metalloids border the stair-step line (with the exception of Al, Po, and At). Metals are on the left side of the chart.

37. Atoms, Molecules, and Ions Exercise 1.Which two of these elements would you expect to show the greatest similarity in chemical and physical properties: B, Ca, F, He, Mg, P? 2.Locate Na (sodium) and Br (bromine) in the periodic table. Give the atomic number of each and classify each as metal, metalloid, or nonmetal. © 2012 Pearson Education, Inc.

38. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.

39. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Chemical Formulas Molecular compounds are composed of molecules and almost always contain only nonmetals.

40. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Diatomic Molecules These seven elements occur naturally as molecules containing two atoms: –Hydrogen –Nitrogen –Oxygen –Fluorine –Chlorine –Bromine –Iodine

41. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Types of Formulas Empirical formulas give the lowest whole- number ratio of atoms of each element in a compound. Molecular formulas give the exact number of atoms of each element in a compound.

42. Atoms, Molecules, and Ions Exercise 1.Write the empirical formulas for (a) glucose, a substance also known as either blood sugar or dextrose, molecular formula C 6 H 12 O 6 ; (b) nitrous oxide, a substance used as an anesthetic and commonly called laughing gas, molecular formula N 2 O. 2.Give the empirical formula for diborane, whose molecular formula is B 2 H 6. © 2012 Pearson Education, Inc.

43. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Types of Formulas Structural formulas show the order in which atoms are bonded. Perspective drawings also show the three-dimensional array of atoms in a compound.

44. Copyright © Cengage Learning. All rights reserved.2 | 44 An ion is an electrically charged particle obtained from an atom or chemically bonded group of atoms by adding or removing one or more electrons.

45. Copyright © Cengage Learning. All rights reserved.2 | 45 A cation is a positively charged ion formed by losing one or more electrons. A cation is named by its element name followed by the word ion. For example, Na + is the sodium ion, etc.

46. Copyright © Cengage Learning. All rights reserved.2 | 46 An anion is a negatively charged ion formed by gaining one or more electrons. An anion is named by changing the last part of the element name to –ide followed by the word ion. For example, F - is the fluoride ion, O 2- is the oxide ion, N 3- is the nitride ion, etc.

47. Copyright © Cengage Learning. All rights reserved.2 | 47 An ionic compound is composed of cations and anions. Ions are arranged in a repeating three-dimensional pattern, forming a crystal. The formula of an ionic compound gives the smallest possible integer number of ions in the substance (without writing charges) so that the combination is electrically neutral. The formula gives the formula unit of the compounds. A formula unit is not a molecule!

48. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: –The charge on the cation becomes the subscript on the anion. –The charge on the anion becomes the subscript on the cation. –If these subscripts are not in the lowest whole- number ratio, divide them by the greatest common factor.

49. Formula of Ionic Compounds Al 2 O 3 2.6 2 x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 2 x+1 = +21 x -2 = -2 Na + CO 3 2-

50. ? Copyright © Cengage Learning. All rights reserved.2 | 50 What is the formula of the ionic compound of Ca 2+ and PO 4 3- ? The common multiple of the charges is 6, so we need three Ca 2+ and two PO 4 3-. The resulting formula is Ca 3 (PO 4 ) 2

51. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Common Cations

52. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Common Anions

53. 13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? 2.5 How many protons and electrons are in ?Al 27 13 3+ How many protons and electrons are in ?Se 78 34 2-

54. Exercise Predict the charge expected for the most stable ion of barium and the most stable ion of oxygen. Answer:

55. Exercise 1.Which of these compounds would you expect to be ionic: N 2 O, Na 2 O, CaCl 2, SF 4 ? 2.Which of these compounds are molecular: CBr 4, FeS, P 4 O 6, PbF 2 ?

56. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Inorganic Nomenclature Write the name of the cation. If the anion is an element, change its ending to -ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion. If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses.

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58. Chemical Nomenclature Ionic Compounds –often a metal + nonmetal –anion (nonmetal), add “ide” to element name BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate 2.7

59. Transition metal ionic compounds –indicate charge on metal with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2 iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3 iron(III) chloride Cr 2 S 3 3 S -2 -6 so Cr is +3 (6/2)chromium(III) sulfide 2.7

60. ? Copyright © Cengage Learning. All rights reserved.2 | 60 What are the names of the following ionic compounds? BaO Cr 2 (SO 4 ) 3 BaO is barium oxide. Cr 2 (SO 4 ) 3 is chromium(III) sulfate or chromic sulfate.

61. ? Copyright © Cengage Learning. All rights reserved.2 | 61 What are the chemical formulas for the following ionic compounds? potassium carbonate manganese(II) sulfate The ions K + and CO 3 2- form K 2 CO 3 The ions Mn 2+ and SO 4 2- form MnSO 4

62. Atoms, Molecules, and Ions Exercise 1.Write the empirical formula of the compound formed by (a) Al 3+ and Cl – ions, (b) Al 3+ and O 2– ions, (c) Mg 2+ and NO 3 – ions. 2.Write the empirical formula for the compound formed by (a) Na + and PO 4 3–, (b) Zn 2+ and SO 4 2– (c) Fe 3+ and CO 3 2–. © 2012 Pearson Education, Inc.

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64. Exercise 1.Name the ionic compounds (a) K 2 SO 4, (b) Ba(OH) 2, (c) FeCl 3. 2.Name the ionic compounds (a) NH 4 Br, (b) Cr 2 O 3, (c) Co(NO 3 ) 2.

65. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Patterns in Oxyanion Nomenclature When there are two oxyanions involving the same element: –The one with fewer oxygens ends in -ite. –The one with more oxygens ends in -ate. NO 2 − : nitrite ; SO 3 2− : sulfite NO 3 − : nitrate; SO 4 2− : sulfate

66. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Patterns in Oxyanion Nomenclature Central atoms on the second row have bond to at most three oxygens; those on the third row take up to four. Charges increase as you go from right to left.

67. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Patterns in Oxyanion Nomenclature The one with the fewest oxygens has the prefix hypo- and ends in -ite. –ClO − : hypochlorite The one with the second fewest oxygens ends in -ite. –ClO 2 − : chlorite The one with the second most oxygens ends in -ate. –ClO 3 − : chlorate The one with the most oxygens has the prefix per- and ends in -ate. –ClO 4 − : perchlorate

68. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Acid Nomenclature If the anion in the acid ends in -ide, change the ending to -ic acid and add the prefix hydro-. –HCl: hydrochloric acid –HBr: hydrobromic acid –HI: hydroiodic acid

69. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Acid Nomenclature If the anion in the acid ends in -ite, change the ending to -ous acid. –HClO: hypochlorous acid –HClO 2 : chlorous acid

70. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Acid Nomenclature If the anion in the acid ends in -ate, change the ending to -ic acid. –HClO 3 : chloric acid –HClO 4 : perchloric acid

71. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Nomenclature of Binary Compounds The less electronegative atom is usually listed first. A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however).

72. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Nomenclature of Binary Compounds The ending on the more electronegative element is changed to -ide. CO 2 : carbon dioxide CCl 4 : carbon tetrachloride If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one. N 2 O 5 : dinitrogen pentoxide

73. ? Copyright © Cengage Learning. All rights reserved.2 | 73 What are the names of the following compounds? OF 2 S 4 N 4 BCl 3 OF 2 is oxygen difluoride S 4 N 4 is tetrasulfur tetranitride BCl 3 is boron trichloride

74. ? Copyright © Cengage Learning. All rights reserved.2 | 74 What are the formulas for the following binary molecular compounds? carbon disulfide nitrogen tribromide dinitrogen tetrafluoride The formula for carbon disulfide is CS 2. The formula for dinitrogen tetrafluoride is N 2 F 4. The formula for nitrogen tribromide is NBr 3.

75. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Nomenclature of Organic Compounds Organic chemistry is the study of carbon. Organic chemistry has its own system of nomenclature.

76. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Nomenclature of Organic Compounds The simplest hydrocarbons (compounds containing only carbon and hydrogen) are alkanes.

77. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Nomenclature of Organic Compounds The first part of the names just listed correspond to the number of carbons (meth- = 1, eth- = 2, prop- = 3, etc.).

78. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Nomenclature of Organic Compounds When a hydrogen in an alkane is replaced with something else (a functional group, like -OH in the compounds above), the name is derived from the name of the alkane. The ending denotes the type of compound. –An alcohol ends in -ol.