1. Chapter 2 Atoms, Molecules, and Ions John D. Bookstaver St. Charles Community College Cottleville, MO Lecture Presentation © 2012 Pearson Education, Inc.

2. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early nineteenth century, championed by John Dalton.

3. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates Each element is composed of extremely small particles called atoms.

4. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.

5. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

6. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Dalton's Postulates Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. ** Law of multiple proportions – compounds always in small whole # ratios

7. 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.

8. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. The Electron Streams of negatively charged particles were found to emanate from cathode tubes, causing fluorescence. J. J. Thomson is credited with their discovery (1897). –Stream was same regardless of cathode material

9. 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).

10. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Millikan Oil-Drop Experiment Once the charge/mass ratio of the electron was known, determination of either the charge or the mass of an electron would yield the other.

11. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Millikan Oil-Drop Experiment Robert Millikan (University of Chicago) determined the charge on the electron in 1909. Electron mass = 1.602 x 10 -19 C = 9.10 x 10 -28 g 1.76 x 10 8 C/g

12. 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. –Tried to isolate radioactive components

13. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Radioactivity Three types of radiation were discovered by Ernest Rutherford: –  particles – high speed He nucleus –  particles – high speed e - –  rays – similar to x-rays

14. 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.

15. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Discovery of the Nucleus Ernest Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.

16. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. The Nuclear Atom Since some particles were deflected at large angles, Thomson’s model could not be correct.

17. 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.

18. Atoms, Molecules, and Ions Practice Exercise 2.1 Atomic Size The diameter of a carbon atom is 1.54 Å. (a) Express this diameter in picometers. (b) How many carbon atoms could be aligned side by side across the width of a pencil line that is 0.20 mm wide? Answer: (a) 154 pm, (b) 1.3  10 6 C atoms

19. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Other Subatomic Particles Protons were discovered by Rutherford in 1919. Neutrons were discovered by James Chadwick in 1932.

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 © 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.

22. 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.

23. 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.

24. Atoms, Molecules, and Ions Practice Exercise 2.2 Determining the Number of Subatomic Particles in Atoms How many protons, neutrons, and electrons are in (a) a 138 Ba atom, (b) an atom of phosphorus-31?

25. Atoms, Molecules, and Ions Sample Exercise 2.3 Writing Symbols for Atoms Give the complete chemical symbol for the atom that contains 82 protons, 82 electrons, and 126 neutrons.

26. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Atomic Mass Atomic and molecular masses and abundances can be measured with great accuracy using a mass spectrometer. Produces chemical “fingerprint” of unknown compounds

27. 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.

28. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Average Mass Calculate the atomic weight of Silicon – 28 Si (92.23%) 27.97693 amu – 29 Si (4.68%) 28.97649 amu – 30 Si (3.09%) 29.97377 amu

29. 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.

30. 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.

31. 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.

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

33. 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).

34. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Periodic Table Metalloids border the stair-step line (with the exception of Al, Po, and At).

35. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Periodic Table Metals are on the left side of the chart.

36. Atoms, Molecules, and Ions Sample Exercise 2.5 Using the Periodic Table Which two of these elements would you expect to show the greatest similarity in chemical and physical properties: B, Ca, F, He, Mg, P? Locate Na (sodium) and Br (bromine) in the periodic table. Give the atomic number of each and classify each as metal, metalloid, or nonmetal. Exercise

37. 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.

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

39. 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

40. 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. –Molecular: C 4 H 10 –Empirical: C 2 H 5

41. 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.

42. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Ions When atoms lose or gain electrons, they become ions. (to have same # of e - as closest noble gas) –Cations are positive and are formed by elements on the left side of the periodic chart. –Anions are negative and are formed by elements on the right side of the periodic chart.

43. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Ionic Bonds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.

44. Atoms, Molecules, and Ions Sample Exercise 2.7 Writing Chemical Symbols for Ions Give the chemical symbol, including superscript indicating mass number, for (a) the ion with 22 protons, 26 neutrons, and 19 electrons How many protons, neutrons, and electrons does the 79 Se 2– ion possess? Practice

45. Atoms, Molecules, and Ions Sample Exercise 2.9 Identifying Ionic and Molecular Compounds Which of these compounds are molecular: CBr 4, FeS, P 4 O 6, PbF 2 ?

46. 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.

47. Atoms, Molecules, and Ions Sample Exercise 2.10 Using Ionic Charge to Write Empirical Formulas for Ionic Compounds 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–.

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

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

50. Atoms, Molecules, and Ions Polyatomic Ions to Memorize Sulfate Phosphate Ammonium Carbonate Nitrate Hydroxide Acetate

51. 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.

52. 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

53. 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.

54. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Patterns in Oxyanion Nomenclature 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

55. 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 most oxygens has the prefix per- and ends in -ate. –ClO 4 − : perchlorate

56. Atoms, Molecules, and Ions Sample Exercise 2.12 Determining the Names of Ionic Compounds from Their Formulas Name the ionic compounds (a) NH 4 Br, (b) Cr 2 O 3, (c) Co(NO 3 ) 2. Give the chemical formulas for (a) magnesium sulfate, (b) silver sulfide, (c) lead(II) nitrate.

57. 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

58. 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

59. 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

60. Atoms, Molecules, and Ions Sample Exercise 2.14 Relating the Names and Formulas of Acids Name the acids (a) HCN, (b) HNO 3, (c) H 2 SO 4, (d) H 2 SO 3. Give the chemical formulas for (a) hydrobromic acid, (b) carbonic acid.

61. 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).

62. 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

63. Atoms, Molecules, and Ions © 2012 Pearson Education, Inc. Nomenclature of Binary Compounds 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

64. Atoms, Molecules, and Ions Sample Exercise 2.15 Relating the Names and Formulas of Binary Molecular Compounds Name the compounds (a) SO 2, (b) PCl 5, (c) Cl 2 O 3. Give the chemical formulas for (a) silicon tetrabromide, (b) disulfur dichloride.

65. 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.

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

67. 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.).

68. 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.