1. Atoms, Molecules, and Ions Chapter 2 Atoms, Molecules, and Ions John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

2. Atoms, Molecules, and Ions Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton.

3. Atoms, Molecules, and Ions Dalton’s Postulates Each element is composed of extremely small particles called atoms. 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. 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. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

4. Atoms, Molecules, and Ions Law of Constant Composition Joseph Proust (1754–1826) Also known as the law of definite proportions. The elemental composition of a pure substance never varies.

5. Atoms, Molecules, and Ions Multiple Proportions 2 compounds can be made from N and O NO – mass N =14.01 mass O =16.00 N/O = N 2 O – mass N = 14.01 mass O = 32.00 N/O = The ratio of the mass ratios is

6. Atoms, Molecules, and Ions 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.

7. Atoms, Molecules, and Ions The Electron Streams of negatively charged particles were found to emanate from cathode tubes. J. J. Thompson is credited with their discovery (1897). Thompson measured the charge/mass ratio of the electron to be 1.76  10 8 coulombs (C)/g

8. Atoms, Molecules, and Ions 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. Robert Millikan (University of Chicago) determined the charge on the electron in 1909.

9. Atoms, Molecules, and Ions Radioactivity: The spontaneous emission of radiation by an atom. First observed by Henri Becquerel. Also studied by Marie and Pierre Curie.

10. Atoms, Molecules, and Ions Radioactivity Three types of radiation were discovered by Ernest Rutherford:   particles   particles   rays

11. Atoms, Molecules, and Ions The Atom, circa 1900: “Plum pudding” model, put forward by Thompson. Positive sphere of matter with negative electrons imbedded in it.

12. Atoms, Molecules, and Ions Discovery of the Nucleus Ernest Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.

13. Atoms, Molecules, and Ions The Nuclear Atom Since some particles were deflected at large angles, Thompson’s model could not be correct.

14. Atoms, Molecules, and Ions 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.

15. Atoms, Molecules, and Ions Other Subatomic Particles Protons were discovered by Rutherford in 1919. Neutrons were discovered by James Chadwick in 1932.

16. Atoms, Molecules, and Ions 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.

17. Atoms, Molecules, and Ions Symbols of Elements Elements are symbolized by one or two letters.

18. Atoms, Molecules, and Ions Atomic Number All atoms of the same element have the same number of protons: The atomic number (Z)

19. Atoms, Molecules, and Ions Atomic Mass The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

20. Atoms, Molecules, and Ions Isotopes: Atoms of the same element with different masses. Isotopes have different numbers of neutrons. 11 6 C 12 6 C 13 6 C 14 6 C

21. Atoms, Molecules, and Ions Atomic Mass Atomic and molecular masses can be measured with great accuracy with a mass spectrometer.

22. Atoms, Molecules, and Ions 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.

23. Atoms, Molecules, and Ions Periodic Table: A systematic catalog of elements. Elements are arranged in order of atomic number.

24. Atoms, Molecules, and Ions Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.

25. Atoms, Molecules, and Ions Periodic Table The rows on the periodic chart are periods. Columns are groups. Elements in the same group have similar chemical properties.

26. Atoms, Molecules, and Ions Groups These five groups are known by their names.

27. Atoms, Molecules, and Ions Periodic Table Nonmetals are on the right side of the periodic table (with the exception of H).

28. Atoms, Molecules, and Ions Periodic Table Metalloids border the stair-step line (with the exception of Al and Po).

29. Atoms, Molecules, and Ions Periodic Table Metals are on the left side of the chart.

30. Atoms, Molecules, and Ions

31. Atoms, Molecules, and Ions Classifying Matter Notes ****ELEMENTS IN THE SAME GROUP ARE SIMILAR**** Trends within groups (top to bottom): a)Atomic Mass- increases as you go down a group. b)Size- increases as you down a group. c)Softness- increases as you go down a group (metals). d)Reactivity- The reactivity increases as you go down for metals BUT the reactivity decreases as you go down (nonmetals) Group 18 (the noble gases) are unreactive. Trends across a period (left to right) a)Atomic Mass- increases as you go left to right across a period. b)Size- gets smaller as you go left to right across a period.

32. Atoms, Molecules, and Ions Organic Chemistry The chemistry of carbon compounds. Carbon has the ability to form long chains. Without this property, large biomolecules such as proteins, lipids, carbohydrates, and nucleic acids could not form.

33. Atoms, Molecules, and Ions Hydrocarbons Contain only C and H Four basic types:  Alkanes – single only  Alkenes -- double bond  Alkynes – triple bond  Aromatic hydrocarbons – “alternating” single and double bonds

34. Atoms, Molecules, and Ions Properties of Alkanes Know the names of the 1-10 carbon alkanes! Intermolecular attractions and thus Boiling and melting points increase with length of chain.

35. Atoms, Molecules, and Ions Functional Groups Term used to refer to parts of organic molecules where reactions tend to occur.

36. Atoms, Molecules, and Ions Alcohols Contain one or more hydroxyl groups, —OH Named from parent hydrocarbon; suffix changed to -ol and number designates carbon to which hydroxyl is attached.

37. Atoms, Molecules, and Ions 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 Molecular Compounds Molecular compounds are composed of molecules and almost always contain only nonmetals.

39. Atoms, Molecules, and Ions Diatomic Molecules These seven elements occur naturally as molecules containing two atoms.

40. Atoms, Molecules, and Ions Types of Formulas Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound.  EXAMPLE – the empirical formula of C 2 H 4 (ethylene) is CH 2 Molecular formulas give the exact number of atoms of each element in a compound.

41. Atoms, Molecules, and Ions 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 Ions When atoms lose or gain electrons, they become ions.  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 Ionic Bonds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.

44. Atoms, Molecules, and Ions 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.

45. Atoms, Molecules, and Ions Nomenclature (Naming) There are different naming rules for: Ionic compounds (metal + nonmetal) Molecular compounds (nonmetals ONLY) Acids (H + cation and an anion) Organic molecules (C first in molecular formula) so to name correctly first you have to decide what kind of compound you have!

46. Atoms, Molecules, and Ions Ionic Naming 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.

47. Atoms, Molecules, and Ions Common Cations

48. Atoms, Molecules, and Ions Common Anions

49. Atoms, Molecules, and Ions Naming Oxyanions Oxyanions contain oxygen and another element. When there are two oxyanions involving the same element:  The one with fewer oxygens ends in -ite NO 2 − : nitrite ; SO 3 2− : sulfite  The one with more oxygens ends in -ate NO 3 − : nitrate; SO 4 2− : sulfate

50. Atoms, Molecules, and Ions Naming Oxyanions When there are four oxyanions involving the same element: 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

51. Atoms, Molecules, and Ions Naming Oxyanions When ions are formed by adding hydrogen to an oxyanion  If there is 1 H+ added, add the word hydrogen to the ion name CO 3 2− : carbonate; HCO 3 − : hydrogen carbonate (aka “bicarbonate”)  If there are 2H+ added, add the word dihydrogen to the ion name PO 4 3− : phosphate; H 2 PO 4 − : dihydrogen phosphate

52. Atoms, Molecules, and Ions Naming Oxyanions

53. Atoms, Molecules, and Ions Acid Nomenclature If the anion in the acid ends in –ide (monatomic), change the ending to -ic acid and add the prefix hydro- :  HCl: hydrochloric acid  HBr: hydrobromic acid  HI: hydroiodic acid

54. Atoms, Molecules, and Ions Acid Nomenclature If the anion in the acid ends in -ite, change the ending to -ous acid:  HNO 2 : nitrous acid  HClO: hypochlorous acid  HClO 2 : chlorous acid

55. Atoms, Molecules, and Ions Acid Nomenclature If the anion in the acid ends in -ate, change the ending to -ic acid:  H 2 SO 4 : sulfuric acid  HClO 3 : chloric acid  HClO 4 : perchloric acid

56. Atoms, Molecules, and Ions 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.)

57. Atoms, Molecules, and Ions Naming Covalent (Molecular) Compounds The ending on the more electronegative element is changed to -ide.  CO 2 : carbon dioxide  CCl 4 : carbon tetrachloride

58. Atoms, Molecules, and Ions Naming Covalent (Molecular) 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