Lecture outline: Chapter 2

Transcription

1 Lecture outline: Chapter 2 1. Atomic structure 2. The Periodic Table 3. Molecules and ions 4. Naming ionic and molecular compounds 1

2 ~400 B.C. Can matter be divided endlessly into smaller and smaller pieces, or is there a point at which it can t be divided anymore?? 2

3 The Atomic Theory of Matter John Dalton: Each element is composed of atoms All atoms of an element are identical. In chemical reactions, the atoms are not changed. Pb + S Compounds are formed when atoms of more than one element combine. 3

4 Dalton s law of multiple proportions Atoms join together in small whole number ratios to make compounds H O H O C O H N H H H H C H H H H C H O H Atoms can combine in different ratios to make different compounds H O H O H H O H N H H H H N N H H 4

5 Atoms of Atoms of Compounds of Mixture of element 1 element 2 elements 1 and 2 elements 1 and 2 O O O O H H H H H H H H H O H O O H H H H H O H H H O 5

6 Observations/studies of two phenomena were key to determining Electricity the structure of the atom Separable charges are associated with matter Radioactivity Atoms are composed of subatomic particles 6

7 Three types of radiation emitted from radioactive uranium Uranium source (-) +2 α particle γ ray (+) -1 β particle Electrically charged plates Detector 7

8 Fun household sources of radioactivity Fiestaware (cirka 1970 and earlier): the orange color comes from uranium salts Lantern mantles (Thorium) Smoke detectors (Americium) 8

9 Atomic Structure: components of the atom electrons Charge: x C (-1) Mass: x g protons: found in the nucleus, they have a positive charge equal in magnitude to the electron s negative charge. Charge: x C (+1) Mass: x g neutrons: found in the nucleus, virtually same mass as a proton but no charge. Charge: Mass: neutral x g 9

10 Atomic structure What are the subatomic particles, how big are they, and how massive are they? How do the subatomic particles associate in atoms? Plum pudding model: (incorrect) 10

11 The Rutherford experiment +2 Alpha particle source Thin gold sheet Detector 11

12 Interpretation of Rutherford s experiment 12

13 The atom is mostly empty space, with the majority of the mass concentrated in a small, dense region Nucleus (proton(s) and neutron(s) ~10-18 cm electron: orbits the nucleus multielectron atoms have more than one e- orbiting the nucleus ~10-13 cm Diameter of atom ~ 10-8 cm (~1-5 Å) 13

14 The electron is ~1000 times smaller in size than the proton, but occupies a space ~10, ,000 times greater than the size of the nucleus Golf ball nucleus on 50 yard line (2 cm diameter) How small is an atom??? The stadium ( 200 m diameter) represents the space in which the electron(s) reside! 14

15 Density of a nucleus? Nucleus (proton(s) and neutron(s) p+ n n p+ p+ p+ n n electron: orbits the nucleus 15

16 Like forces repel, opposites attract, so What holds the nucleus together? Why don t the electrons fall into the nucleus?? Nucleus (proton(s) and neutron(s) p+ n n p+ p+ p+ n n electron: orbits the nucleus 16

17 Four basic attractive forces in nature Ma agnitude of force inc creases Gravitational (masses) Electromagnetic (electrically charged and/or magnetized) Weak nuclear force Strong nuclear force p+ n n p+ p+ p+ n n 17

18 What defines the atoms of a single element? If all atoms consists of protons, neutrons, and electrons, then what makes oxygen oxygen and carbon carbon? 18

19 Elements are classified on the basis of the number of protons in the nucleus All atoms of a given element have the same number of protons in the nucleus Z= atomic number = # of protons in the nucleus 19

20 Elements are classified on the basis of the number of fprotons in the nucleus All atoms of a given element have the same number of protons in the nucleus Z= atomic number = # of protons in the nucleus 20

21 How many neutrons and electrons #e - =#p + # neutrons can vary in a given atom? Σ (# p + + # n) = mass # 21

22 Atomic Symbols Mass number A Atomic number Z X Element Symbol 39K Mass number 39 19K Element Symbol Atomic number 22

23 Isotopes: atoms of an element that differ in the number of neutrons in the nucleus Isotopes have the same atomic number but different mass numbers 23

24 Two isotopes of carbon Carbon-12 n p+ n n p+ n p+ n p+ Carbon-13 p+ n p+ n p+ n n n p+ n p+ n p+ p+ n p+ 6 protons 6 neutrons 6 protons 7 neutrons 12 C 13 C

25 Hydrogen, the simplest element 25

26 Silver has two isotopes: one with 60 neutrons, one with 62 neutrons. What are the mass numbers and symbols of these isotopes? For silver (Ag), Z = 47 26

27 Give the complete symbol A Z X for each of the following atoms Sodium with 12 neutrons argon with 21 neutrons For Na, Z = 11 For Ar, Z = 18 Gallium with 39 neutrons For Ga, Z = 31 27

28 How many e -, p + and n are present in an atom of: 40 Ca See the Periodic 119 Sn Table to find the atomic numbers for these elements 244 Pu 28

29 Complete the following table using the Periodic Table and the information provided Symbol 46 Ti 127 Te # protons 45 # neutrons Atomic # Mass # 88 29

30 What is the origin of the name of the uncola beverage 7 up? 30

31 Atomic weights: We will cover this material in lecture 7 31

32 The Periodic Table 32

33 The Periodic Table 33

34 The Periodic Table Horizontal rows = periods n = 1,2,3,4,5,6,7 n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 n=7 n = 6 n = 7 34

35 The Periodic Table vertical columns = families or groups n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 n=7 n = 6 n = 7 35

36 The Periodic Table Metals, metalloids, and nonmetals 36

37 The Periodic Table Some important group names Noble gases halogens The transition metals 37 Alkaline earth metals Alkali metals

38 Elements within groups (families) have similar chemical properties 38

39 Elements within groups (families) have similar chemical properties Chemical properties of alkali metals: react vigorously with water to produce hydrogen gas React vigorously with oxygen to produce metal hydroxides React vigorously with halogens to produce salts Physical properties of alkali metals: Soft metal Silver-colored Low density Low melting and boiling points 39

40 Elements Essential for Life 40

41 Molecular and ionic compounds 114 elements by themselves = ~114 substances (yawn) Glue different elements together in different ratios infinite number of potentially interesting compounds!! 41

42 A molecule (molecular compound; covalent compound) An assembly of two or more nonmetal atoms, tightly bound (bonded) together Molecules of a single atom Molecules of more than one type of atom 42

43 Chemical formulas for molecules Molecular formula: the actual numbers of atoms of each element in the compound Empirical formula: the simplest whole number ratio of elements in the compound 43

44 Some compounds cannot be represented by a molecular formula Allotropes of carbon: diamond, graphite, and buckyball Graphite, C n diamond, C n buckyball, C 6044

45 Structural formula A pictorial representation of a molecular formula. Shows how the atoms are joined together. 45

46 Molecular formula: the numbers of atoms of each element in the molecule NH 3 Structural formula: A pictorial representation showing how atoms are connected (arranged) in the compound Perspective drawing: A structural t formula providing information about the 3-dimensional shape of the molecule Ball and stick model: A perspective drawing where bonded atoms are shown as balls and sticks Space filling model: A 3-dimensional model showing the relative sizes of individual atoms and their distances from one another 46

47 Subscripts and superscripts For an element, subscripts and superscripts to the LEFT of the element indicate the atomic number and mass number of that element 32 P 15 For a compound, subscripts to the RIGHT of the elements tell us how many atoms of that element are present in the compound (no subscript = 1) CH 4, C 2 H 4, CO 2, H 2 O, NH 3 47

48 Ions: atoms that have gained or lost electrons and hence have a net negative or positive charge. The nucleus of the atom remains unchanged. Cations: electron(s) removed X n+ Anions: electron(s) added Y n- 48

49 Formation of a sodium cation Remove one e - 11 p+ 11 p+ 11 p + 11 p + 11 e - 10 e - Na Na 1+ = Na + 49

50 Formation of a chloride anion add one e - 17 p+ 17 p+ 17 p + 17 p + 17 e - 18 e - Cl Cl - 50

51 Ions Metal atoms lose electrons to form cations Nonmetal atoms gain electrons to make anions WHY?? 51

52 Many atoms gain or lose electrons in order to obtain the same number of electrons as a nearby noble gas H + H - Li + N 3- O 2- F - Na + Mg 2+ Al 3+ P 3- S 2- Cl - K + Ca 2+ S 2- Br - Rb + Sr 2+ Te 2- I - Cs + Ba 2+ 52

53 Predict the charges on the ions formed by the following elements: Element nearest noble gas ion Na Mg Cs Ra F Cl O N P Al C 53

54 Complete the following table using the Periodic Table and the information provided Symbol 85 Y 120 Sn Te # protons 65 # neutrons # electrons Atomic # 53 Mass # 127 Charge

55 Binary ionic compounds Combinations of metal cations and nonmetal anions bonded together through strong electrostatic attractive forces (an ionic bond ) Contrast molecular compounds, which are formed from combinations of nonmetals only (H 2 O, CO 2,CH 4, etc.) bonded by shared electron pairs in a covalent bond Combinations of metalloids and nonmetals are usually classified as molecular S. Ensign, S. Atomic Ensign, structure Chem. & 1210 nomenclature 55

56 Reaction of Na and Cl Ionic compounds are always represented by empirical formulas: there is no discrete molecular formula for an ionic solid 56

57 Writing empirical formulas for ionic compounds A compound with only 2 elements is a binary compound For ionic i compounds, place the symbol for the metal before that of the nonmetal (cation first, anion second) Subscripts after the elements designate the number of atoms of that type in the compound When writing the formula of a neutral ionic compound, net charge = 0, so the charges must balance for each ion 57

58 Writing empirical formulas for ionic compounds A compound with only 2 elements is a binary compound For ionic compounds, place the symbol for the metal before that of the nonmetal (cation first, anion second) Subscripts after the elements designate the number of atoms of that type in the compound When writing the formula of a neutral ionic compound, net charge = 0, so the charges must balance for each ion 58

59 Writing empirical formulas for ionic compounds A compound with only 2 elements is a binary compound For ionic compounds, place the symbol for the metal before that of the nonmetal (cation first, anion second) Subscripts after the elements designate the number of atoms of that type in the compound When writing the formula of a neutral ionic compound, net charge = 0, so the charges must balance for each ion 59

60 Polyatomic ions: a compound of two or more nonmetal atoms, joined through covalent bonds, that forms a single charged unit (i.e., a molecular compound that does not have a neutral charge) SO 3 is a molecular compound SO 4 2- is a polyatomic anion NH 3 is a molecular compound NH 4+ is a polyatomic cation 4 p y 60

61 Common polyatomic ions Name Formula Charge Ammonium ion NH Nitrate ion NO Chlorate ion ClO Carbonate ion CO Sulfate ion SO Peroxide ion O Phosphate ion PO

62 Ionic compounds containing polyatomic ions Name Formula Charge Ammonium ion NH X m Y n Nitrate ion NO Chlorate ion ClO Carbonate ion CO Sulfate ion SO Peroxide ion O Phosphate ion PO

63 A fail proof way to write the correct formula for an ionic compound X n+ Y m- m n X Y m n Reduce to an empirical i formula, if necessary, by dividing idi by the appropriate integer (e.g. Mg 2 O 2 MgO) 63

64 A fail proof way to deduce the ion charges on ions present in an ionic compound n+ m- X Y m n X n+ Y m- Be sure the magnitude of the ion charge matches what it should be based on position in the periodic table for a monatomic ion, or the known charge for a polyatomic ion 64

65 Write empirical formulas for the binary ionic i compounds formed from the combinations of Co 2+, Mg 2+, and Li + with S 2-, PO 4 3-, and SO

66 Classify the following compounds as ionic or molecular. Which molecular formulas are also empirical formulas? compound Type? Empirical? NF 3 C 6 H 14 K 2 S P 4 S 3 MgO KBr OF 2 AsH 3 XeF 2 NaF PbF 2 P 2 F 4 66

67 Nomenclature: The naming of substances Be able to name: Constituent atoms in molecular compounds Constituent t ions in ionic i compounds Ionic compounds Molecular l compounds Acids Ionic compounds are named using a different set of rules than covalent compounds 67

68 Naming ionic compounds Cation name followed by anion name So, how do we name cations and anions? 68

69 Naming monatomic cations (+ ions) Cations for which only one charge can be formed (group 1A, 2A, 3A, some d block): the name is simply the name of the metal followed by ion Cations of transition ( d block ) metals that can form more than one charge: New method: Place the charge in parentheses after the metal name and before ion old method for metals that form two charges: use root of latin name + ous for lower charge, or ic for higher charge, followed by ion 69

70 Naming monatomic cations (+ ions) Cations for which only one charge can be formed (group 1A, 2A, 3A, some d block): the name is simply the name of the metal followed by ion 70

71 Naming monatomic cations (+ ions) Cations of transition metals that can form more than one charge: New method: Place the charge in parentheses after the metal name and before ion old method for metals that form two charges: use root of latin name + ous for lower charge, or ic for higher charge, followed by ion 71

72 There aren t many polyatomic cations to worry about Common polyatomic ions Name Formula Charge Ammonium ion NH Nitrate ion NO Chlorate ion ClO Carbonate ion CO Sulfate ion SO Peroxide ion O Phosphate ion PO

73 Naming monatomic anions (- ions) Drop the ending of the name of the element and add ide + ion H - N 3- O 2- F - S 2- Br - 73

74 There are a lot more polyatomic anions to worry about 74

75 Making sense of polyatomic anion names Some of them also end in ide Hydroxide (know this one now) Cyanide Peroxide azide 75

76 Making sense of polyatomic anion names XO m- n Elements that form only 2 oxyanions: Oxyanions are very common Charges on both ions are generally the same One with less oxygens = ite One with more oxygens = ate Elements that form 3 or 4 oxyanions: Charges on both ions are generally the same hypo = less per = more Hydrogen ions (H + ) can combine with oxyanions to form new hydrogen oxyanions 76

77 Making sense of polyatomic anion names XO m- n Note I am going g to give you the formulas and names for the following oxyanions on the exam information sheet. At some point you will need to memorize these though. Formulas and names of common polyatomic ions: Carbonate ion = CO 2-3 Sulfate ion = SO 2-4 Nitrate ion = NO - 3 Perchlorate ion = ClO - 4 Phosphate h ion = PO

78 Making sense of polyatomic anion names Elements that form only 2 oxyanions: Charges on both ions are generally the same One with less oxygens = ite One with more oxygens = ate XO m- n Formulas and names of common polyatomic ions: Carbonate ion = CO 2-3 Sulfate ion = SO 2-4 Nitrate ion = NO 3 - Perchlorate ion = ClO 4 - Phosphate ion = PO 4 3- Nitrogen combines with O to form two common oxyanions that have one N: NO 2- and NO 3 - oxyanions that have one N: NO 2 and NO 3 Since we know from the table that NO 3- is the nitrate ion, we can predict that NO 2- is the nitrite ion Note the ion charges on NO 2- and NO 3- are the same (-1 in each case) 78

79 Making sense of polyatomic anion names Elements that form only 2 oxyanions: Charges on both ions are generally the same One with less oxygens = ite One with more oxygens = ate XO m- n Formulas and names of common polyatomic ions: Carbonate ion = CO 2-3 Sulfate ion = SO 2-4 Nitrate ion = NO 3 - Perchlorate ion = ClO 4 - Phosphate ion = PO 4 3- Sulfur combines with O to form two common oxyanions that have one S: SO 3 2- and SO 4 2- oxyanions that have one S: SO 3 and SO 4 Since we know from the table that SO 2-4 is the sulfate ion, we can predict that SO 2-3 is the sulfite ion Note the ion charges on SO 2- and SO are the same (-2 in each case) 79

80 Making sense of polyatomic anion names Elements that form only 2 oxyanions: Charges on both ions are generally the same One with less oxygens = ite One with more oxygens = ate XO m- n Formulas and names of common polyatomic ions: Carbonate ion = CO 2-3 Sulfate ion = SO 2-4 Nitrate ion = NO 3 - Perchlorate ion = ClO 4 - Phosphate ion = PO 4 3- Phosphorus combines with O to form two common oxyanions: PO 3 3- and PO 4 3- common oxyanions: PO 3 and PO 4 Since we know from the table that PO 3-4 is the phosphate ion, we can predict that PO 3-3 is the phosphite ion Note the ion charges on PO 3- and PO are the same (-3 in each case) 80

81 Making sense of polyatomic anion names XO m- n Carbon combines with O to form only common oxyanion with one C: CO 2-3 CO 3 2- is the carbonate ion, and there is no such thing as the carbonite ion Formulas and names of common polyatomic ions: Carbonate ion = CO 2-3 Sulfate ion = SO 2-4 Nitrate ion = NO - 3 Perchlorate ion = ClO - 4 Phosphate ion = PO

82 Making sense of polyatomic anion names Elements that form 4 oxyanions: XO n-, where X is a halogen (Cl, Br, I) and n = Formulas and names of common polyatomic ions: 1-4 Carbonate ion = CO 2-3 Sulfate ion = SO 2-4 Nitrate ion = NO 3 - Perchlorate ion = ClO 4 - Phosphate ion = PO 4 3- Charges on all 4 ions are the same (-1) Take the root of the halogen (chlor, bromo, iodo) Hypo ite = XO - (e.g. hypochlorite) ite = XO 2- (e.g. chlorite) ate = XO 2- (e.g. chlorate) Per ate = XO 4- (e.g. perchlorate) 82

83 Oxyanions can also be formed with the formulas X p- n O mp and have names that are not easy to predict. You do not need to memorize or be familiar with any of these for chemistry 1210 S 2 O 3 2- is the thiosulfate ion S 2 O 2-4 is the dithionate t ion S 4 O 2-6 is the tetrathionate ion 83

84 There are a few oxyanions consisting of metals combined with oxygens, bonded similarly to the bonds between nonmetals and oxygens in oxyanions. You don t need to memorize the names of these now, but here are a couple common ones. MnO 4- = permanganate ion (used widely in gen chem labs) Cr 2 O 2-7 = dichromate ion (also used widely in gen chem labs) 84

85 Oxyanion examples Elements that form only 2 oxyanions: XO n m- Charges on both ions are generally the same One with less oxygens = ite One with more oxygens = ate Elements that form 3 or 4 oxyanions: Charges still the same hypo = less per = more Hydrogen ions (H + ) can combine with oxyanions to form new hydrogen oxyanions 85

86 Information I will give you on exam Formulas and names of common polyatomic ions: Carbonate ion = CO Nitrate ion = NO 3 3- Phosphate ion = PO 4 2- Sulfate ion = SO 4 - Perchlorate ion = ClO 4 + Ammonium ion = NH 4 You must know the hydroxide ion (OH - ) 86

87 Naming ionic compounds: Cation Cti name followed fll dby anion name Examples: Name the following ionic compounds: CaBr 2 Mg(OH) 2 Co 2 O 3 TiCl 2 Formulas and names of common polyatomic ions: 2- Carbonate ion = CO 3 - Nitrate ion = NO 3 3- Phosphate ion = PO 4 2- Sulfate ion = SO 4 - Perchlorate ion = ClO 4 Ammonium ion = NH + 4 (NH 4 4) 2 CO 3 Na 2 SO 4 NaHSO 4 Wherever possible, predict charges on simple cations and anions based on positions in periodic table 87

88 Acids A simple working definition (for now): a compound that dissolves in water to produce hydrogen ions and a corresponding anion H n X 88

89 Binary acids: Begin with hydro Naming acids H n X Follow hydro with anion name, replacing ide with ic Complete the naming with acid n 89

90 Adding hydrogens to oxyanions to form neutral acids: mh + + XO n m- H m XO n Change ite ion to ous acid Change ate ion to ous acid Retain hypo or per if they are present 90

91 Oxyanion ion Formula Oxyacid Formula Nitrite ion NO 2 - Nitrous acid HNO 2 Nitrate ion NO 3 - Nitric acid HNO 3 Hypochlorite ion ClO 3 - Hypochlorous acid HClO chlorite ion ClO 2 - Chlorous acid HClO 2 chlorate ion ClO 3 - Chloric acid HClO 3 Perchlorate ion ClO 4 - Perchloric acid HClO 4 Carbonate ion CO 2-3 Carbonic acid H 2 CO 3 Sulfate ion SO 3 2- Sulfurous acid H 2 SO 3 Sulfate ion SO 4 2- Sulfuric acid H 2 SO 4 Phosphite ion PO 3 3- Phosphorous acid H 3 PO 3 Phosphate ion PO 4 3- Phosphoric acid H 3 PO 4 91

92 Naming molecular compounds Nonmetal + nonmetal Many are binary 92

93 Naming binary molecular compounds: In general, the element closer to the metals is listed first the first element in the formula is named first, using it s normal elemental name For the second element in the formula, drop the ending of the element name and replace with ide Use prefixes to indicate the number(s) of atom(s) in the binary compounds (don t use mono for 1st element) -Mono -Di -Tri -Tetra -penta 93

94 Prefixes used when naming binary molecular compounds Prefix Meaning mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7 nona 8 deca 9 94

95 Naming binary molecular compounds: In general, the element closer to the metals is listed first the first element in the formula is named first, using it s normal elemental name For the second element in the formula, drop the ending of the element name and replace with ide Use prefixes to indicate the number(s) of atom(s) in the binary compounds (don t use mono for 1st element) 95

96 Name these molecular and ionic compounds compound Type? Empirical? Name NF 3 C 6 H 14 K 2 S P 4 S 3 MgO KBr OF 2 AsH 3 XeF 2 NaF PbF 2 P 2 F 4 96

97 Give formulas for each of the following ionic compounds a) Ammonium nitrate b) Cobalt (II) nitrate c) Nickel (II) sulfate d) Nickel (III) cyanide e) Vanadium (III) oxide f) Ammonium sulfate Formulas and names of common polyatomic ions: 2- Carbonate ion = CO 3 - Nitrate ion = NO 3 3- Phosphate ion = PO 4 2- Sulfate ion = SO 4 - Perchlorate ion = ClO 4 + Ammonium ion = NH 4 97

98 Name the following compounds: a) MgBr 2 b) Li 2 CO 3 c) KHSO 3 d) KMnO 4 e) (NH 4 ) 2 S f) CuCl g) CuCl 2 98

99 a) Carbon dioxide Give formulas for: b) Phosphorus s triiodide c) Sulfur dichloride d) Xenon trioxide e) Dioxygen difluoride 99

100 Name the following molecular compounds: a) N 2 F 4 b) HBr c) SF 4 d) ClF 3 e) BCl 3 f) P 4 O