2. Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 4 Atoms and Elements

3. Tro's Introductory Chemistry, Chapter 4 2 Experiencing Atoms Atoms are very small; they are building blocks of matter. Atom = smallest particle of an element that retains its characteristics

4. Tro's Introductory Chemistry, Chapter 4 3 Dalton’s Atomic Theory 1. Elements are composed of tiny indivisible particles called atoms 2. All atoms of an element are identical; atoms of different elements are different –every carbon atom is identical to every other carbon atom they have the same chemical and physical properties –but carbon atoms are different from sulfur atoms they have different chemical and physical properties John Dalton (1766-1844)

5. Tro's Introductory Chemistry, Chapter 4 4 Dalton’s Atomic Theory 3. Atoms combine in simple, whole- number ratios to form molecules of compounds –each molecule of a compound contains the exact same types and numbers of atoms Law of Constant Composition or Definite Proportions Chemical Formulas

6. Tro's Introductory Chemistry, Chapter 4 5 Dalton’s Atomic Theory 4. In chemical reactions, atoms are not broken or changed into other atoms. –atoms are not created or destroyed, just rearranged total mass will remain the same Law of Conservation of Mass –atoms of one element do not change into atoms of another element in a chemical reaction cannot turn Lead into Gold by a chemical reaction

7. Tro's Introductory Chemistry, Chapter 4 6 Dalton’s Atomic Theory Law of multiple proportions : if two elements A and B combine to form more than one compound, masses of B which combine with mass of A, is a ratio of small whole numbers. Ex: CO, (1.33 g O/1g C); CO 2 (2.67 g O/g) The mass of O in CO 2 is twice that in CO: 2.67g O in CO 2 /1.33 g O in CO 2 = 2.00 Thus, when 2 elements combine to form 2 different compounds, they combine in different ratios or proportions: CO, CO 2 ; SO 2, SO 3

8. Tro's Introductory Chemistry, Chapter 4 7 Modern Evidence for Atoms Atoms can be seen through a special instrument called the scanning tunneling microscope (STM)

9. Tro's Introductory Chemistry, Chapter 4 8 Mass of Atoms Using compositions of compounds and assumed formulas, Dalton determined relative masses of atoms Dalton based his scale on H = 1 amu we now base it on C-12 = 12 amu exactly unit = atomic mass unit, amu

10. Tro's Introductory Chemistry, Chapter 4 9 The Atom is Divisible! electrons Work done by J.J. Thomson and others proved that the atom had particles called electrons Thomson found that electrons are much smaller than atoms and carry a negative charge The mass of the electron is 1/1836 th the mass of a hydrogen atom

11. Tro's Introductory Chemistry, Chapter 4 10 Rutherford’s Experiment Lead Box Radioactive Sample Gold Foil Fluorescent Screen Alpha Particles Striking Screen

12. Tro's Introductory Chemistry, Chapter 4 11 Conclusions from Rutherford’s Experiment Atom mostly empty space –because most particles went through Atom contains a dense particle that was small in volume compared to the atom but large in mass –because of the few particles that bounced back This dense particle was positively charged –because of the large deflections of some of the particles

13. 12 Rutherford’s Interpretation – the Nuclear Model 1) Atom contains a tiny dense center called the nucleus 2) The nucleus has essentially the entire mass of the atom –the electrons weigh so little they give practically no mass to the atom 3) The nucleus is positively charged –the amount of positive charge balances the negative charge of the electrons 4) The electrons move around in the empty space of the atom surrounding the nucleus

14. Tro's Introductory Chemistry, Chapter 4 13 The Modern Atom Atoms are composed of three particles - protons, neutrons and electrons The nucleus contains protons and neutrons The electrons move outside the nucleus Neutral atom has same # protons and electrons.

15. 14 + + The Nuclear Atom: protons neutrons -Nucleus electrons -

16. Tro's Introductory Chemistry, Chapter 4 15 Subatomic Particles: neutrons (n) protons (p) electrons (e) Charge?Location?

17. Tro's Introductory Chemistry, Chapter 4 16 Subatomic Particles: 0 nucleus +1 nucleus -1 outside neutronprotonelectron Charge?Location? Charge? Location?

18. Tro's Introductory Chemistry, Chapter 4 17 11  0 (1/1837) neutronprotonelectron Mass (amu) Subatomic Particles:

19. Tro's Introductory Chemistry, Chapter 4 18 Elements Each element has a unique number of protons in its nucleus Number of protons in the nucleus of an atom is called the atomic number –the elements are arranged on the Periodic Table in order of their atomic numbers Each element has a unique name and symbol –symbol either one or two letters one capital letter or one capital letter + one lower case

20. Tro's Introductory Chemistry, Chapter 4 19 How many? protons = depends on element neutrons = variable for each element electrons = same as protons

21. Tro's Introductory Chemistry, Chapter 4 20 atomic number - The number of protons in one atom; each element has a different atomic number The number on top of the element symbol in the periodic table

22. Tro's Introductory Chemistry, Chapter 4 21 The Periodic Table of Elements The Periodic Table of Elements

23. Tro's Introductory Chemistry, Chapter 4 22 Review What is the atomic number of boron, B? What is the atomic mass of silicon, Si? How many protons does a chlorine atom have? How many electrons does a neutral neon atom have? Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral? Will an atom with 27 protons, 32 neutrons and 27 electrons be electrically neutral? Will a Na atom with 10 electrons be electrically neutral?

24. Tro's Introductory Chemistry, Chapter 4 23Review What is the atomic number of boron, B? 5 What is the atomic mass of silicon, Si? 28.09 amu How many protons does a chlorine atom have? 17 How many electrons does a neutral neon atom have? 10 Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral? Yes Will an atom with 27 protons, 32 neutrons and 27 electrons be electrically neutral? Yes Will a Na atom with 10 electrons be electrically neutral? No

25. Three Types of Elements = Metal = Metalloid = Nonmetal

26. Tro's Introductory Chemistry, Chapter 4 25 Metals Solids at room temperature, except Hg Shiny Conduct heat, electricity Malleable: can be shaped Ductile = drawn or pulled into wires Lose electrons and form cations (+ charge) in reactions About 75% of the elements are metals

27. Tro's Introductory Chemistry, Chapter 4 26 Nonmetals Found in all 3 states Poor conductors of heat & electricity Solids are brittle Gain electrons in reactions to become anions (- charge) Only a few on the right of periodic table

28. Tro's Introductory Chemistry, Chapter 4 27 Metalloids Show some properties of metals and some of nonmetals Also known as semiconductors Properties of Silicon shiny conducts electricity does not conduct heat well brittle

29. Tro's Introductory Chemistry, Chapter 4 28 The Modern Periodic Table Elements with similar chemical and physical properties are in same column Columns are called Groups or Families –designated by a number and letter at top Rows are called Periods Each period shows the pattern of properties repeated in the next period

30. Tro's Introductory Chemistry, Chapter 4 29 The Modern Periodic Table Main Group = Representative Elements = ‘A’ groups Transition Elements = ‘B’ groups –all metals Bottom rows = Inner Transition Elements = Rare Earth Elements –metals –really belong in Period 6 & 7

31. Tro's Introductory Chemistry, Chapter 4 30 = Alkali Metals = Alkali Earth Metals = Noble Gases = Halogens = Lanthanides = Actinides = Transition Metals

32. Tro's Introductory Chemistry, Chapter 4 31 Important Groups - Hydrogen nonmetal colorless, diatomic gas –very low melting point & density reacts with nonmetals to form molecular compounds –HCl is acidic gas –H 2 O is a liquid reacts with metals to form hydrides –metal hydrides react with water to form H 2 HX dissolves in water to form acids

33. 32 Important Groups – IA, Alkali Metals hydrogen usually placed here, though it doesn’t belong soft, low melting points,low density very reactive, never find uncombined in nature tend to form water soluble compounds react with water to form basic (alkaline) solutions and H 2 releasing a lot of heat lithium sodium potassium rubidium cesium

34. Tro's Introductory Chemistry, Chapter 4 33 Important Groups – IIA, Alkali Earth Metals harder, higher melting, and denser than alkali metals reactive, but less than corresponding alkali metal form stable, insoluble oxides from which they are normally extracted oxides are basic = alkaline earth magnesium calcium beryllium strontium barium

35. Tro's Introductory Chemistry, Chapter 4 34 Important Groups – VIIA, Halogens nonmetals F 2 & Cl 2 gases; Br 2 liquid; I 2 solid all diatomic very reactive react with metals to form ionic compounds HX all strong acids except HF bromine iodine chlorine fluorine

36. Tro's Introductory Chemistry, Chapter 4 35 Important Groups – VIIIA, Noble Gases all gases at room temperature, –very low melting and boiling points very unreactive, practically inert very hard to remove electron from or give an electron to

37. Tro's Introductory Chemistry, Chapter 4 36 Charged Atoms = Ions Number of protons (atomic #) identifies the element! –all sodium atoms have 11 protons in the nucleus In chemical change, number of protons in nucleus of atom doesn’t change! Atoms can lose or gain electrons becoming electrically charged, these are called ions

38. Tro's Introductory Chemistry, Chapter 4 37 Ions Atoms acquire a charge by gaining or losing electrons –not protons!! Ion Charge = # protons – # electrons ions with a + charge are called cations –more protons than electrons –form by losing electrons ions with a – charge are called anions –more electrons than protons –form by gaining electrons

39. Tro's Introductory Chemistry, Chapter 4 38 Atomic Structures of Ions Metals form cations For each positive charge the ion has 1 less electron than the neutral atom –Na atom = 11 p + and 11 e -, Na + ion = 11 p + and 10 e - –Ca atom = 20 p + and 20 e -, Ca 2+ ion = 20 p + and 18 e - Cations are named the same as the metal sodiumNa  Na + + 1e - sodium ion calciumCa  Ca 2+ + 2e - calcium ion The charge on a cation can be determined from the Group number on the Periodic Table –Group 1A  +1, Group 2A  +2, (Al, Ga, In)  +3

40. Tro's Introductory Chemistry, Chapter 4 39 Atomic Structures of Ions Nonmetals form anions For each negative charge the ion has 1 more electron than the neutral atom –F = 9 e -, F - = 10 e - –P = 15 e -, P 3- = 18 e - Anions are named by changing the ending of the name to -ide fluorineF + 1e -  F - fluoride ion oxygenO + 2e -  O -2 oxide ion Charge on an anion can be determined by subtracting 8 from the Group number on the Periodic Table –Group 7A  7- 8 = -1; Group 6A  6 – 8 = -2

41. Example 4.5: Determining the Number of Protons and Electrons in an Ion

42. Tro's Introductory Chemistry, Chapter 4 41 Example: Find the number of protons and electrons in the Ca 2+ ion.

43. Tro's Introductory Chemistry, Chapter 4 42 Example: Find the number of protons and electrons in the Ca 2+ ion Write down the given quantity and its units.  Given: Ca 2+

44. Tro's Introductory Chemistry, Chapter 4 43 Example: Find the number of protons and electrons in the Ca 2+ ion Write down the quantity to find and/or its units.  Find: #p and #e Information Given: Ca 2+

45. Tro's Introductory Chemistry, Chapter 4 44 Design a Solution Map. ion symbol element #p atomic number Example: Find the number of protons and electrons in the Ca 2+ ion Information Given: Ca 2+ Find:#p and #e #e and #e Ion charge = #p - #e

46. Tro's Introductory Chemistry, Chapter 4 45 Apply the Solution Map. –Determine the Name of the Element Example: Find the number of protons and electrons in the Ca 2+ ion Information Given: Ca 2+ Find:#p and #e Solution Map: ion symbol  element  atomic number  #p  #e Ca = calcium

47. Tro's Introductory Chemistry, Chapter 4 46 Apply the Solution Map. –Determine the Atomic Number of the Element Example: Find the number of protons and electrons in the Ca 2+ ion Information Given: Ca 2+ = calcium Find:#p and #e Solution Map: ion symbol  element  atomic number  #p  #e Ca = calcium Atomic Number = 20

48. Tro's Introductory Chemistry, Chapter 4 47 Apply the Solution Map. –Determine the Number of Protons in an Atom of the Element Example: Find the number of protons and electrons in the Ca 2+ ion Information Given: Ca 2+ = calcium, Z = 20 Find:#p and #e Solution Map: ion symbol  element  atomic number  #p  #e Ca = calcium Atomic Number = 20 #p = atomic number = 20

49. Tro's Introductory Chemistry, Chapter 4 48 Apply the Solution Map. –Determine the Number of Electrons in an Ion of the Element Example: Find the number of protons and electrons in the Ca 2+ ion Information Given: Ca 2+ = calcium, Z = 20 Find:#p = 20 and #e Solution Map: ion symbol  element  atomic number  #p  #e Ca = calcium Atomic Number = 20 #p = atomic number = 20 Ion Charge = #p - #e +2 = 20 - #e -18 = - #e 18 = #e

50. Tro's Introductory Chemistry, Chapter 4 49 Atomic Structures of Ions

51. Tro's Introductory Chemistry, Chapter 4 50 Atomic Structures of Ions

52. Tro's Introductory Chemistry, Chapter 4 51 Ion Charge & the Periodic Table Charge on an ion can often be determined from an element’s position on the Periodic Table Metals are always positive ions, nonmetals are negative ions For many main group metals, the charge = the group number For nonmetals, the charge = the group number - 8

53. Tro's Introductory Chemistry, Chapter 4 52 Li +1 Na +1 K +1 Rb +1 Cs +1 Be + Be +2 Mg +2 Ca +2 Sr +2 Ba +2 Al +3 Ga +3 In +3 O -2 S -2 Se -2 Te -2 F -1 Cl -1 Br -1 I -1 N -3 P -3 As -3 IA IIAIIIA VIIA VIA VA Charges of Main Group Ions

54. Tro's Introductory Chemistry, Chapter 4 53 Isotopes Isotopes = atoms of an element that have same # of protons but different # of neutrons Isotopes of an element have different masses isotopes are identified by their –mass numbers = protons + neutrons All isotopes of an element are chemically identical –undergo the exact same chemical reactions

55. Tro's Introductory Chemistry, Chapter 4 54 Atomic Number Number of protons Z (symbol) Mass Number Protons + Neutrons Whole number A (symbol) Abundance = relative amount found in a sample Isotopes

56. Tro's Introductory Chemistry, Chapter 4 55 Neon 9.25%221210Ne-22 0.27%211110Ne-21 90.48%201010Ne-20 Percent Natural Abundance A, Mass Number Number of Neutrons Number of Protons Symbol

57. Tro's Introductory Chemistry, Chapter 4 56 Isotope Symbols Cl-35 makes up about 75% of chlorine atoms in nature, and Cl-37 makes up the remaining 25% Cl-35 makes up about 75% of chlorine atoms in nature, and Cl-37 makes up the remaining 25% Average atomic mass of Cl = 35.45 amu Average atomic mass of Cl = 35.45 amu Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17) Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17) X = Atomic Symbol A = mass number Z = atomic number AXAX Z Cl 35 17 or Cl-35

58. Example 4.8: Determining the Number of Protons and Neutrons from Isotope Symbols

59. Tro's Introductory Chemistry, Chapter 4 58 Example: How many protons and neutrons in the chromium isotope

60. Tro's Introductory Chemistry, Chapter 4 59 Example: How many protons and neutrons in the chromium isotope Write down the given quantity and its units.  Given:

61. Tro's Introductory Chemistry, Chapter 4 60 Write down the quantity to find and/or its units.  Find:#p and #n InformationGiven: Example: How many protons and neutrons in the chromium isotope

62. Tro's Introductory Chemistry, Chapter 4 61 Design a Solution Map. ion symbol element #p atomic numberInformationGiven: Find:#p and #n #n Example: How many protons and neutrons in the chromium isotope Mass # = #p + #n

63. Tro's Introductory Chemistry, Chapter 4 62 Apply the Solution Map. –Determine the Name of the Element InformationGiven: Find:#p and #n Solution Map: ion symbol  element  atomic number  #p  #n Cr = chromium Example: How many protons and neutrons in the chromium isotope

64. Tro's Introductory Chemistry, Chapter 4 63 Apply the Solution Map. –Determine the Atomic Number of the Element Information Given: = calcium Find:#p and #n Solution Map: ion symbol  element  atomic number  #p  #n Cr = chromium Atomic Number = 24 Example: How many protons and neutrons in the chromium isotope

65. Tro's Introductory Chemistry, Chapter 4 64 Apply the Solution Map. –Determine the Number of Protons in an Atom of the Element Cr = chromium Atomic Number = 24 #p = atomic number = 24 Information Given: = calcium Find:#p and #n Solution Map: ion symbol  element  atomic number  #p  #n Example: How many protons and neutrons in the chromium isotope

66. Tro's Introductory Chemistry, Chapter 4 65 Apply the Solution Map. –Determine the Number of Neutrons in an Atom of the Element Cr = chromium Atomic Number = 24 #p = atomic number = 24 Mass Number = #p + #n 52 = 24 + #n 28 = #n Information Given: = calcium Find:#p and #n Solution Map: ion symbol  element  atomic number  #p  #n Example: How many protons and neutrons in the chromium isotope

67. Tro's Introductory Chemistry, Chapter 4 66 Practice - Complete the following table

68. Tro's Introductory Chemistry, Chapter 4 67 Practice - Complete the following table

69. Tro's Introductory Chemistry, Chapter 4 68 Mass Number is Not the Same as Atomic Mass The atomic mass is an experimental number determined from all naturally occurring isotopes The mass number refers to the number of protons + neutrons in one isotope –natural or man-made