1. Chapter 10 Molecular Structure: Solids and Liquids

2. Homework Assigned Problems (odd numbers only) Assigned Problems (odd numbers only) “Questions and Problems” 10.1 to 10.53 (begins on page 292) “Questions and Problems” 10.1 to 10.53 (begins on page 292) “Additional Questions and Problems” 10.65 to 10.91 (page 325) “Additional Questions and Problems” 10.65 to 10.91 (page 325) “Challenge Questions” 10.93 to 10.99, (page 327) “Challenge Questions” 10.93 to 10.99, (page 327)

3. Representing Valence Electrons with Dots: Electron-Dot Formulas The valence electrons are the most important (chemically) electrons in the atom The valence electrons are the most important (chemically) electrons in the atom These electrons are situated in the highest, occupied principal energy level (n) These electrons are situated in the highest, occupied principal energy level (n) They are farthest from the nucleus, away from the stable (filled) inner core of electrons They are farthest from the nucleus, away from the stable (filled) inner core of electrons Determine the chemical properties of an element Determine the chemical properties of an element

4. Representing Valence Electrons with Dots: Electron-Dot Formulas In the main-group elements, the valence electrons are the in the outermost s- and p- orbitals In the main-group elements, the valence electrons are the in the outermost s- and p- orbitals The Roman numeral at the top of each column represents the number of valence electrons in each member of that group The Roman numeral at the top of each column represents the number of valence electrons in each member of that group The valence electrons for the main-group elements can be represented by Lewis Structures The valence electrons for the main-group elements can be represented by Lewis Structures

5. Representing Valence Electrons with Dots: Electron-Dot Formulas The Lewis (Dot) structure consists of an elements symbol with one dot per each valence electron placed about the element’s symbol The Lewis (Dot) structure consists of an elements symbol with one dot per each valence electron placed about the element’s symbol The representative elements in the same group have the same number of valence electrons The representative elements in the same group have the same number of valence electrons The maximum number of valence electrons for any element is eight The maximum number of valence electrons for any element is eight

6. Representing Valence Electrons with Dots: Electron-Dot Formulas Only the noble gases have the maximum number of eight electrons Only the noble gases have the maximum number of eight electrons The exception is helium with only two valence electrons The exception is helium with only two valence electrons Octet rule Duet rule

7. Representing Valence Electrons with Dots: Electron-Dot Formulas Example: dot structures for representative elements in period 2 Example: dot structures for representative elements in period 2 The valence electrons are in the outer s and p orbitals The valence electrons are in the outer s and p orbitals Li Be B C N O: :F: :Ne: outer electron configuration ns 1 ns 2 np 1 ns 2 ns 2 np 2 ns 2 np 3 ns 2 np 4 ns 2 np 5 ns 2 np 6

8. Representing Valence Electrons with Dots: Electron-Dot Formulas The force of attraction between two types of atoms is a chemical bond The force of attraction between two types of atoms is a chemical bond The ionic bond is the attraction between positive and negative ions The ionic bond is the attraction between positive and negative ions Compounds held together by ionic bonds are called ionic compounds Compounds held together by ionic bonds are called ionic compounds Each element forms an ion with a stable noble gas configuration Each element forms an ion with a stable noble gas configuration

9. Lewis Structures for Ionic Compounds: Electrons Transferred During ionic bond formation, ions form when atoms of two elements are present: An element that can lose electrons and an element that can gain electrons During ionic bond formation, ions form when atoms of two elements are present: An element that can lose electrons and an element that can gain electrons The most stable of all outer electron configurations is based on the chemical properties of the noble gases The most stable of all outer electron configurations is based on the chemical properties of the noble gases By chemical reactions and compound formation, elements can attain a stable outer electron configuration By chemical reactions and compound formation, elements can attain a stable outer electron configuration

10. Lewis Structures for Ionic Compounds: Electrons Transferred Metals: Low ionization energy, form ions (cations) Metals: Low ionization energy, form ions (cations) Nonmetals: High ionization energy, accept electrons (anions) Nonmetals: High ionization energy, accept electrons (anions) The representative elements lose or gain electrons to form ions with outer electron configuration of the nearest noble gas The representative elements lose or gain electrons to form ions with outer electron configuration of the nearest noble gas

11. Electron Configuration of Ions An ion: An atom that is electrically charged from loss or gain of electrons An ion: An atom that is electrically charged from loss or gain of electrons Atoms are neutral due to the equal number of protons and electrons Atoms are neutral due to the equal number of protons and electrons Loss or gain of an electron will leave a net charge on the atom Loss or gain of an electron will leave a net charge on the atom

12. Electron Configuration of Ions Consider sodium Consider sodium Can attain the noble gas configuration (neon) if it loses 1 electron to obtain Na + Can attain the noble gas configuration (neon) if it loses 1 electron to obtain Na + Noble gas core remains but it does not have the same chemical properties of neon Noble gas core remains but it does not have the same chemical properties of neon 1s 2 2s 2 2p 6 3s 1 Na Loss of 1 e - 1s 2 2s 2 2p 6 Electron configuration of neon Na +

13. Electron Configuration of Ions Consider chlorine Consider chlorine Can attain the noble gas configuration (argon) if it gains 1 electron to obtain Cl - Can attain the noble gas configuration (argon) if it gains 1 electron to obtain Cl - Attains same E configuration of the nearest noble gas but it does not have the same chemical properties of argon Attains same E configuration of the nearest noble gas but it does not have the same chemical properties of argon 1s 2 2s 2 2p 6 3s 2 3p 5 Cl Gain of 1 e - 1s 2 2s 2 2p 6 3s 2 3p 6 Electron configuration of argon Cl -

14. Electron Configurations We know for Representative Elements: We know for Representative Elements: Group 1A metals form ions with +1 chargeGroup 1A metals form ions with +1 charge Group 2A metals form ions with +2 chargeGroup 2A metals form ions with +2 charge Group 7A nonmetals form ions with -1 chargeGroup 7A nonmetals form ions with -1 charge Group 6A nonmetals form ions with -2 chargeGroup 6A nonmetals form ions with -2 charge Group 8A nonmetals do not form ions, in fact they are extremely unreactiveGroup 8A nonmetals do not form ions, in fact they are extremely unreactive Transition Elements: All of the elements of the d area of the periodic table Transition Elements: All of the elements of the d area of the periodic table Elements differ in the number of electrons in the d subshellElements differ in the number of electrons in the d subshell Octet rule does not apply hereOctet rule does not apply here Loss of electrons does not lead to the noble gas structureLoss of electrons does not lead to the noble gas structure

15. Ions of the Metals of Groups IA, IIA, IIIA Metals form cations by losing enough electrons to get the same electron configuration as the previous noble gas Metals form cations by losing enough electrons to get the same electron configuration as the previous noble gas A stable noble gas core attained in each case A stable noble gas core attained in each case

16. Ions of the Nonmetals of Group VIA, VIIA Nonmetals form anions by gaining enough electrons to get the same electron configuration as the next noble gas Nonmetals form anions by gaining enough electrons to get the same electron configuration as the next noble gas A stable noble gas core attained in each case A stable noble gas core attained in each case

17. Lewis Structures for Ionic Compounds: Electrons Transferred Lewis Structures for Ionic Compounds: Electrons Transferred Sodium Chloride Sodium Chloride Formed from sodium and chlorine atomsFormed from sodium and chlorine atoms An ionic bond forms consisting of a sodium ion (+ charge) and a chloride ion (- charge)An ionic bond forms consisting of a sodium ion (+ charge) and a chloride ion (- charge) Each sodium loses one electron to achieve an octet Each chlorine atom gains one electron to achieve an octet Formula is NaCl Na + Cl Na + [ F ] -

18. Lewis Structures for Ionic Compounds: Electrons Transferred Magnesium Chloride Magnesium Chloride Formed from magnesium and two chlorinesFormed from magnesium and two chlorines An ionic bond forms consisting of a magnesium ion (2+ charge) andAn ionic bond forms consisting of a magnesium ion (2+ charge) and two chloride ions (- charge each) Each magnesium loses two electrons to achieve an octet Each chlorine atom gains one electron to achieve an octet Formula is MgCl 2

19. Lewis Structures for Ionic Compounds: Electrons Transferred Bonding involves ONLY valence electrons Bonding involves ONLY valence electrons Transfer of the s and p valence electrons achieves stability of the nearest noble gas Transfer of the s and p valence electrons achieves stability of the nearest noble gas Illustrates the sequence of atoms Illustrates the sequence of atoms Shows atoms and their valence electrons Shows atoms and their valence electrons How they are distributed in a moleculeHow they are distributed in a molecule Use a dot or X to represent an electronUse a dot or X to represent an electron Li Be B C N O: :F: :Ne: Li Li 1+ :F: [:F:] 1-

20. Give the number of valence electrons for Mg, N, and Br. Draw the Lewis dot symbol for each of these elements Give the number of valence electrons for Mg, N, and Br. Draw the Lewis dot symbol for each of these elements Lewis Structures for Ionic Compounds: Electrons Transferred Mg: 2 valence electrons N: 5 valence electrons Br: 7 valence electrons Mg Br N

21. Covalent Lewis Structures: Electrons Shared Chemical bonding also occurs between two nonmetals Chemical bonding also occurs between two nonmetals Since nonmetals do not readily lose electrons, when two nonmetals bind together the electrons are shared Since nonmetals do not readily lose electrons, when two nonmetals bind together the electrons are shared A covalent bond is a pair of electrons shared by two atoms A covalent bond is a pair of electrons shared by two atoms It is the binding force that results from two nuclei attracting the same shared electrons It is the binding force that results from two nuclei attracting the same shared electrons

22. Covalent Lewis Structures: Electrons Shared A covalent Lewis structure: A 2-D representation of how atoms are covalently bonded together A covalent Lewis structure: A 2-D representation of how atoms are covalently bonded together Each covalent bond is represented by a pair of dots (bonding electrons) Each covalent bond is represented by a pair of dots (bonding electrons) Must also show all unshared pairs of (nonbonding) electrons Must also show all unshared pairs of (nonbonding) electrons All valence e - from every atom in a molecule must be accounted for in the form of bonds or nonbonding pairs All valence e - from every atom in a molecule must be accounted for in the form of bonds or nonbonding pairs

23. Covalent Lewis Structures: Electrons Shared The atoms in covalently bonded molecules often have bonding and nonbonding electrons The atoms in covalently bonded molecules often have bonding and nonbonding electrons The number of covalent bonds that an atom forms is equal to the number of electrons needed to form a noble gas configuration (octet) The number of covalent bonds that an atom forms is equal to the number of electrons needed to form a noble gas configuration (octet) The exception is hydrogen which needs only two electrons The exception is hydrogen which needs only two electrons Shared electrons can be also represented by dashes Shared electrons can be also represented by dashes

24. Formation of a Hydrogen Molecule The simplest covalent bonding condition The simplest covalent bonding condition Hydrogen has one 1s electron Hydrogen has one 1s electron H atom requires one additional electron to obtain the stable noble gas configuration of helium H atom requires one additional electron to obtain the stable noble gas configuration of helium Each H atom contributes its one electron Each H atom contributes its one electron The electron pair shared by the two atoms, forming diatomic hydrogen H 2 The electron pair shared by the two atoms, forming diatomic hydrogen H 2

25. Covalent Lewis Structure: Electrons Shared Duet Rule Duet Rule Hydrogen wants two electrons to attain the noble gas configuration of heliumHydrogen wants two electrons to attain the noble gas configuration of helium Octet Rule Octet Rule All other main group elements want 8 electrons to achieve the noble gas configurationAll other main group elements want 8 electrons to achieve the noble gas configuration Filled valence shell is achieved by gaining/losing electrons or by sharing electronsFilled valence shell is achieved by gaining/losing electrons or by sharing electrons

26. Covalent Lewis Structures: Double and Triple Bonds A single covalent bond is where two atoms share one pair of valence electrons A single covalent bond is where two atoms share one pair of valence electrons Many molecules exist that need two or three pairs of electrons to provide a complete octet of electrons per atom Many molecules exist that need two or three pairs of electrons to provide a complete octet of electrons per atom Multiple covalent bonds: Covalent bonds where two pairs or three pairs of valence electrons are shared between the same two atoms Multiple covalent bonds: Covalent bonds where two pairs or three pairs of valence electrons are shared between the same two atoms

27. Covalent Lewis Structures: Double and Triple Bonds Two identical nonmetal atoms (diatomic molecules) Two identical nonmetal atoms (diatomic molecules) Each atom will share valence electrons with the other Each atom will share valence electrons with the other The shared pair of electrons allow each atom to achieve a stable noble gas configuration The shared pair of electrons allow each atom to achieve a stable noble gas configuration This configuration can be achieved by a single, double, or triple shared pair of electrons This configuration can be achieved by a single, double, or triple shared pair of electrons ●● ●●●

28. Covalent Lewis Structures: Double and Triple Bonds Single Bond is a chemical bond where two atoms share one pair of valence electrons Single Bond is a chemical bond where two atoms share one pair of valence electrons Double Bond is a chemical bond where two atoms share two pairs of valence electrons Double Bond is a chemical bond where two atoms share two pairs of valence electrons Triple Bond is a chemical bond where two atoms share three pairs of valence electrons Triple Bond is a chemical bond where two atoms share three pairs of valence electrons

29. Sharing Electrons Between Atoms of Different Elements Two nonidentical nonmetal atoms Two nonidentical nonmetal atoms The number of covalent bonds an atom forms will equal the number of electrons needed to form a stable, noble gas configuration The number of covalent bonds an atom forms will equal the number of electrons needed to form a stable, noble gas configuration Hydrogen follows the duet rule and forms a stable, helium noble gas configuration Hydrogen follows the duet rule and forms a stable, helium noble gas configuration

30. Bonding Behavior of Elements Oxygen has 6 valence electrons and 2 octet vacancies Oxygen has 6 valence electrons and 2 octet vacancies Can complete its octet by forming two covalent bonds Can complete its octet by forming two covalent bonds Nitrogen has 5 valence electrons and 3 octet vacancies Nitrogen has 5 valence electrons and 3 octet vacancies Can complete its octet by forming three covalent bonds Can complete its octet by forming three covalent bonds Group 6A Group 5A

31. Bonding Behavior of Elements Carbon has 4 valence electrons and 4 octet vacancies Carbon has 4 valence electrons and 4 octet vacancies Can complete its octet by forming four covalent bonds Can complete its octet by forming four covalent bonds Fluorine has 7 valence electrons and 1 octet vacancy Fluorine has 7 valence electrons and 1 octet vacancy Can complete its octet by forming one covalent bond Can complete its octet by forming one covalent bond Group 7A Group 4A

32. Bonding Behavior of Elements Group 4A Group 5A Group 6AGroup 7A

33. Writing Lewis Structures for Covalent Compounds A dot structure is a two-dimensional representation of a molecule to show how atoms are joined together by covalent bonding A dot structure is a two-dimensional representation of a molecule to show how atoms are joined together by covalent bonding To write a dot structure: To write a dot structure: A bond is shown as a pair of dots or a dash A bond is shown as a pair of dots or a dash Dot structures also show the location of electron pairs not used in bonds Dot structures also show the location of electron pairs not used in bonds All valence electrons from every atom in the molecule or PA ion must be accounted for All valence electrons from every atom in the molecule or PA ion must be accounted for

34. Writing Lewis Structures for Covalent Compounds 1) Determine the arrangement of atoms within a molecule If there are three or more atoms, the central atom (usually) appears only once in the formulaIf there are three or more atoms, the central atom (usually) appears only once in the formula Halogens are often terminal atoms (at the ends) unless it is combined with O as in oxyacidsHalogens are often terminal atoms (at the ends) unless it is combined with O as in oxyacids Hydrogen is always a terminal atomHydrogen is always a terminal atom

35. Writing Lewis Structures for Covalent Compounds 2) Determine the total number of valence electrons For main-group elements the group numbers equal the number of valence electrons for the element of that group For main-group elements the group numbers equal the number of valence electrons for the element of that group If it is an anion, add one electron to the total for each negative chargeIf it is an anion, add one electron to the total for each negative charge If it is a cation, subtract one electron from the total for each positive chargeIf it is a cation, subtract one electron from the total for each positive charge

36. Writing Lewis Structures for Covalent Compounds 3) Attach the central atom to each bonded atom by a pair of electrons Subtract two electrons (from total valence) for each single bond drawn in the structureSubtract two electrons (from total valence) for each single bond drawn in the structure

37. Writing Lewis Structures for Covalent Compounds 4) Distribute the remaining electrons Add electrons to each atom bonded to the central atom until each has eight electrons (octet rule) Add electrons to each atom bonded to the central atom until each has eight electrons (octet rule) Exception: hydrogen (duet rule) Exception: hydrogen (duet rule) Any extra electrons should go to the central atoms Any extra electrons should go to the central atoms

38. Writing Lewis Structures for Covalent Compounds 5) If the central atom does not fulfill the octet rule, share one or more lone pairs between a terminal atom and the central atom (form multiple covalent bonds) Double or triple bonds are formed ONLY when one or both of the atoms are C, N, O or S Double or triple bonds are formed ONLY when one or both of the atoms are C, N, O or S

39. Writing Lewis Structures for Covalent Compounds Example: Create the electron-dot formula for Fluorine gas = F 2 Determine the arrangement of the atoms Determine the arrangement of the atoms Determine the total number of valence electrons for the dot structure (2 × 7 = 14)Determine the total number of valence electrons for the dot structure (2 × 7 = 14) Begin with bonding electronsBegin with bonding electrons Distribute the remaining electrons among the two atoms, giving octets to each fluorine atom, then proceed to lone pairs on each atomDistribute the remaining electrons among the two atoms, giving octets to each fluorine atom, then proceed to lone pairs on each atom F ●

40. Writing Lewis Structures for Covalent Compounds and Polyatomic Ions Write a Lewis structure for the following: Write a Lewis structure for the following: NH 4 +NH 4 + SO 4 2-SO 4 2- COCO SCN -SCN -

41. Writing Lewis Structures for Covalent Compounds: CO Determine the arrangement of the atoms Determine the arrangement of the atoms C: 4 electrons C: 4 electrons O: 6 electrons O: 6 electrons Total valence electrons: 10 Total valence electrons: 10 If octets are not complete, form one or more multiple covalent bonds If octets are not complete, form one or more multiple covalent bonds

42. Writing Lewis Structures for Polyatomic Ions: NH 4 + Determine the arrangement of the atoms Determine the arrangement of the atoms Total number of valence e - Total number of valence e - N: 5 valence electrons N: 5 valence electrons H: 4×1 valence electron H: 4×1 valence electron Positive Charge: Subtract one electron Positive Charge: Subtract one electron Total valence electrons: 8 Total valence electrons: 8

43. Writing Lewis Structures for Polyatomic Ions: SO 4 2- Determine the arrangement of the atoms Determine the arrangement of the atoms Total number of valence electrons Total number of valence electrons S: 6 valence electrons S: 6 valence electrons O: 4 x 6 valence electrons O: 4 x 6 valence electrons Negative Charge: Add two electrons Negative Charge: Add two electrons Total valence electrons: 32 Total valence electrons: 32

44. Writing Lewis Structures for Polyatomic Ions: SCN - Determine the arrangement of the atoms Determine the arrangement of the atoms Total number of valence electrons: Total number of valence electrons: S: 6 electronsS: 6 electrons C: 4 electronsC: 4 electrons N: 5 electronsN: 5 electrons Charge: add one electron Charge: add one electron Total electrons: 16 Total electrons: 16 If octets are not complete, form one or more multiple covalent bonds If octets are not complete, form one or more multiple covalent bonds

45. Resonance: Equivalent Lewis Structures for the Same Molecule Resonance occurs when no single dot structure adequately describes bonding in molecule Resonance occurs when no single dot structure adequately describes bonding in molecule Resonance structures are two or more dot structures for a molecule or ion that has the same arrangement of atoms Resonance structures are two or more dot structures for a molecule or ion that has the same arrangement of atoms Contain the same number of electrons Contain the same number of electrons Differ only in the location of electrons Differ only in the location of electrons The true structure is the average of the individual structures The true structure is the average of the individual structures

46. Writing Resonance Structures Write a Lewis structure for nitrate ion and include resonance structures Write a Lewis structure for nitrate ion and include resonance structures Determine the arrangement of the atoms Determine the arrangement of the atoms Total number of valence electrons Total number of valence electrons Use a double-headed arrow to connect the structures Use a double-headed arrow to connect the structures (3 ×6) + 5 + 1 = 24 valence elec

47. Writing Resonance Structures Write a Lewis structure for ozone and include resonance structures (O 3 ) Write a Lewis structure for ozone and include resonance structures (O 3 ) Determine the arrangement of the atoms Determine the arrangement of the atoms Total number of valence electrons Total number of valence electrons The actual structure is called a “resonance hybrid” of the two contributing structures The actual structure is called a “resonance hybrid” of the two contributing structures Resonance structuresHybrid 3 ×6 = 18 valence elec

48. Writing Resonance Structures

49. Predicting the Shapes of Molecules (Lewis) Dot structures describe the distribution of valence electrons among bonding pairs and nonbonding pairs (Lewis) Dot structures describe the distribution of valence electrons among bonding pairs and nonbonding pairs They do not give info on the 3-D shape of the molecule They do not give info on the 3-D shape of the molecule The 3-D arrangement of atoms in a molecule is determined by its molecular geometry The 3-D arrangement of atoms in a molecule is determined by its molecular geometry

50. Predicting the Shapes of Molecules A Lewis structure for water A Lewis structure for water Are the atoms arranged in a straight line or do they form a v-shape? Are the atoms arranged in a straight line or do they form a v-shape?

51. Predicting the Shapes of Molecules VSEPR Theory The 3-D shapes of molecules and PA ions result from the orientation of atoms about the central atom The 3-D shapes of molecules and PA ions result from the orientation of atoms about the central atom VSEPR: Valence Shell Electron-Pair Repulsion Theory focuses on the bonding and nonbonding electrons in the valence shell of the central atom VSEPR: Valence Shell Electron-Pair Repulsion Theory focuses on the bonding and nonbonding electrons in the valence shell of the central atom

52. Predicting the Shapes of Molecules VSEPR Theory The central atom’s electrons play an important role in determining molecular shape The central atom’s electrons play an important role in determining molecular shape Bonding and nonbonding pairs of electrons have a natural electrostatic repulsion that pushes them as far apart from one another as possible Bonding and nonbonding pairs of electrons have a natural electrostatic repulsion that pushes them as far apart from one another as possible

53. Predicting the Shapes of Molecules VSEPR Theory It is this repulsion of electron groups (regions of negative charge) that causes a molecule to have a certain shape: molecular geometry It is this repulsion of electron groups (regions of negative charge) that causes a molecule to have a certain shape: molecular geometry The central concept of VSEPR theory is that the electron pairs in the valence shell of atoms form an arrangement in space that minimizes the repulsion between the electron pairs: electron geometry The central concept of VSEPR theory is that the electron pairs in the valence shell of atoms form an arrangement in space that minimizes the repulsion between the electron pairs: electron geometry

54. Electron Geometries Two electron groups Two electron groups 2 atoms attached2 atoms attached Shape: LinearShape: Linear Bond angle: 180°Bond angle: 180° Three electron groups Three electron groups 3 atoms attached3 atoms attached Shape: Trigonal PlanarShape: Trigonal Planar Bond angle: 120°Bond angle: 120° Four electron groups Four electron groups 4 atoms attached4 atoms attached Shape: TetrahedralShape: Tetrahedral Bond angle 109.5°Bond angle 109.5°

55. Molecular Geometries Linear 2 electron groups2 electron groups 2 bonding groups, 0 lone pairs2 bonding groups, 0 lone pairs 2 atoms on opposite sides of the central atom2 atoms on opposite sides of the central atom 180° bond angles180° bond angles Trigonal Planar Trigonal Planar 3 electron groups3 electron groups 3 bonding groups, 0 one pairs3 bonding groups, 0 one pairs 3 atoms form a triangle around the central atom3 atoms form a triangle around the central atom 120° bond angles120° bond angles 180° 120°

56. Molecular Geometries Tetrahedral Tetrahedral 4 electron groups4 electron groups 4 bonding groups, 0 lone pairs4 bonding groups, 0 lone pairs 4 surrounding atoms form a tetrahedron around the central atom4 surrounding atoms form a tetrahedron around the central atom 109.5° bond angles109.5° bond angles 109.5°

57. Predicting the Shapes of molecules VSEPR Theory Example: beryllium fluoride Example: beryllium fluoride 2 electron groups and 2 bonding groups2 electron groups and 2 bonding groups 0 lone pairs0 lone pairs Beryllium does not follow the octet ruleBeryllium does not follow the octet rule Electron geometry: linearElectron geometry: linear Angle between electron groups: 180°Angle between electron groups: 180° Molecular geometry: linearMolecular geometry: linear 180°

58. Shapes of molecules and ions VSEPR Theory Example: boron trifluoride Example: boron trifluoride 3 electron groups, 3 bonding groups, 0 lone pairs3 electron groups, 3 bonding groups, 0 lone pairs Boron does not follow the octet ruleBoron does not follow the octet rule Electron geometry: trigonal planarElectron geometry: trigonal planar Angle between electron groups: 120°Angle between electron groups: 120° Molecular geometry: trigonal planarMolecular geometry: trigonal planar 120°

59. Shapes of molecules and ions VSEPR Theory Example: carbon tetrafluoride Example: carbon tetrafluoride 4 electron groups, 4 bonding groups, 0 lone pairs 4 electron groups, 4 bonding groups, 0 lone pairs Electron geometry: tetrahedral Electron geometry: tetrahedral Angle between electron groups: 109.5° Angle between electron groups: 109.5° Molecular geometry: tetrahedral Molecular geometry: tetrahedral 109.5°

60. VSEPR Theory: Central Atoms with Bonding Pairs and Lone Pairs Often the 3-D shape (molec. geometry) is not described the same as the electron geometry Often the 3-D shape (molec. geometry) is not described the same as the electron geometry The electron-pair geometry around a central atom includes the spatial positions of all bond pairs and lone pairs The electron-pair geometry around a central atom includes the spatial positions of all bond pairs and lone pairs Only the arrangement of atoms describes the molecular geometry of the molecule, not the lone pairs of electrons because you can’t actually see lone pairs, you can only see the atoms Only the arrangement of atoms describes the molecular geometry of the molecule, not the lone pairs of electrons because you can’t actually see lone pairs, you can only see the atoms

61. VSEPR Theory: Central Atoms with Bonding Pairs and Lone Pairs Example: ammonia gas Example: ammonia gas 4 electron groups, 3 bonding groups, 1 lone pair 4 electron groups, 3 bonding groups, 1 lone pair 3 atoms attached to the central atom 3 atoms attached to the central atom A tetrahedral electron geometry A tetrahedral electron geometry Angle between electron groups: 109.5° Angle between electron groups: 109.5° A trigonal pyramidal molecular geometry A trigonal pyramidal molecular geometry

62. VSEPR Theory: Central atoms with Bonding Pairs and Lone Pairs Example: Water Example: Water 4 electron groups, 2 bonding groups, 2 lone pairs 4 electron groups, 2 bonding groups, 2 lone pairs 2 atoms attached to the central atom 2 atoms attached to the central atom A tetrahedral electron geometry A tetrahedral electron geometry Angle between electron groups: 109.5° Angle between electron groups: 109.5° A bent molecular geometry A bent molecular geometry

63. Electronegativity and Polarity Electronegativity is the ability of an atom in a molecule to attract bonding electrons towards itself Electronegativity is the ability of an atom in a molecule to attract bonding electrons towards itself The higher the element’s electronegativity, the greater its ability to attract electrons The higher the element’s electronegativity, the greater its ability to attract electrons

64. Electronegativity and Polarity Electronegativity Electronegativity Increases across a period (left to right) on the periodic tableIncreases across a period (left to right) on the periodic table Decreases down group (top to bottom) on the periodic tableDecreases down group (top to bottom) on the periodic table In general: In general: Nonmetals have higher electronegativity values than metals and nonmetals tend to gain electronsNonmetals have higher electronegativity values than metals and nonmetals tend to gain electrons Metals have lower electronegativity values and tend to lose electronsMetals have lower electronegativity values and tend to lose electrons This occurs when an ionic bond is formedThis occurs when an ionic bond is formed

65. Electronegativity Fluorine (the reference element) is most electronegative, Cesium (Francium) is least electronegative Fluorine (the reference element) is most electronegative, Cesium (Francium) is least electronegative

66. Polarity of Bonds A covalent bond involves pairs of electrons shared equally between two atoms A covalent bond involves pairs of electrons shared equally between two atoms How they are shared (equally or unequally) depends on the electron donating and electron attracting nature of the atoms How they are shared (equally or unequally) depends on the electron donating and electron attracting nature of the atoms As the electronegativity difference increases between two elements, bond polarity increases As the electronegativity difference increases between two elements, bond polarity increases

67. Polarity of Bonds Nonpolar (Pure) covalent bond Nonpolar (Pure) covalent bond Two identical atoms will share the bonding electrons equallyTwo identical atoms will share the bonding electrons equally Polar covalent bond Polar covalent bond Two different atoms will not share the bonding electrons equallyTwo different atoms will not share the bonding electrons equally One atom will have a greater attraction for the shared pair than the other atomOne atom will have a greater attraction for the shared pair than the other atom Ionic bond Ionic bond Results from the transfer of one or more electrons from one atom to anotherResults from the transfer of one or more electrons from one atom to another

68. Electronegativity Bond polarity measures the amount of unequal sharing of electrons in a chemical bond Bond polarity measures the amount of unequal sharing of electrons in a chemical bond The difference in electronegativity values determines the extent of polarity in a bond The difference in electronegativity values determines the extent of polarity in a bond As the bond polarity increases, the bond becomes more ionic As the bond polarity increases, the bond becomes more ionic

69. Electronegativity General guidelines related to electronegativity differences General guidelines related to electronegativity differences Bonds with a difference of zero are nonpolar (pure) covalent Bonds with a difference of zero are nonpolar (pure) covalent Bonds with differences greater than 0.4 but less than 2.0 are called polar covalent bonds Bonds with differences greater than 0.4 but less than 2.0 are called polar covalent bonds Bonds with differences 2.0 or greater are called ionic Bonds with differences 2.0 or greater are called ionic Molecule O2O2O2O2CO Mg 2 O Electronegativity Values 3.5 and 3.5 2.5 and 3.5 1.2 and 3.5 Electronegativity Difference 0.01.02.3 Bond Type Pure Covalent Polar Covalent Ionic

70. Electronegativity Increases across period (left to right) on Periodic Table Increases across period (left to right) on Periodic Table Decreases down group (top to bottom) on Periodic Table Decreases down group (top to bottom) on Periodic Table Larger difference in electronegativities means more polar bond Larger difference in electronegativities means more polar bond Negative end toward more electronegative atomNegative end toward more electronegative atom MoleculeO-OC-OMg-O Electronegativity Values 3.5 and 3.5 2.5 and 3.5 1.2 and 3.5 Electronegativity Difference 0.01.02.3 Bond Type Pure Covalent Polar Covalent Ionic

71. Polarity of Bonds/Dipole Moments In a polar covalent bond: One of the two different elements will inevitably have a greater attraction for the shared pair than the other In a polar covalent bond: One of the two different elements will inevitably have a greater attraction for the shared pair than the other This unequal sharing causes the entire molecule to behave like an electric dipole (dipole moment) This unequal sharing causes the entire molecule to behave like an electric dipole (dipole moment) Dipole: A body with two poles, one partially negative and one positive Dipole: A body with two poles, one partially negative and one positive

72. Polar Bonds and Polar Molecules Molecules (as well as bonds) can have polarity Molecules (as well as bonds) can have polarity A polar molecule has an unsymmetrical distribution of electronic charge: The bonding electrons are more attracted to one part of the molecule more than other parts A polar molecule has an unsymmetrical distribution of electronic charge: The bonding electrons are more attracted to one part of the molecule more than other parts The polarity of a molecule has two factors: The polarity of a molecule has two factors: Bond polarities Bond polarities Molecular geometry Molecular geometry

73. Polar Bonds and Polar Molecules If a molecule contains only polar bonds does not mean the molecule as a whole is polar If a molecule contains only polar bonds does not mean the molecule as a whole is polar Polarity will depend on whether or not the polarity effects cancel each other Polarity will depend on whether or not the polarity effects cancel each other

74. Polar Bonds and Polar Molecules In a water molecule, oxygen draws the shared pair of electrons closer to oxygen and partially withdrawn from hydrogen In a water molecule, oxygen draws the shared pair of electrons closer to oxygen and partially withdrawn from hydrogen Since the dipoles do not cancel, water is a polar molecule Since the dipoles do not cancel, water is a polar molecule Since the dipoles do cancel, SO 3 is a nonpolar molecule Since the dipoles do cancel, SO 3 is a nonpolar molecule In a sulfur trioxide molecule, oxygen draws the shared pair of electrons closer and partially withdrawn from sulfur In a sulfur trioxide molecule, oxygen draws the shared pair of electrons closer and partially withdrawn from sulfur

75. end

76. Kinetic molecular theory of matter states that the particles present in any phase of matter are in constant, random motion: thermal energy The thermal (kinetic) energy is temperature dependent The particles interact together through attractions and repulsions that creates potential energy within the particles

77. Thermal (kinetic) and potential energy in a chemical system influence the chemical properties of a system Kinetic energy gives the particles their motion and tends to move the particles away from each other Potential energy is an attractive force which attracts the particles together

78. The relative influence of kinetic and potential energy is the main consideration when KM theory is used to explain the general properties of the gas, liquid, or solid states of matter The type of energy that dominates will influence a substance’s physical state

79. Molecules in a liquid do not have all the same kinetic energy These differences in energy are due to collisions between the molecules The molecules near the surface, above the average KE, can escape the intermolecular forces holding them in the liquid phase

80. Interactions between Molecules Intermolecular Forces are forces that act between a molecule and another molecule They are electrostatic forces that are similar to the intramolecular forces involved in covalent bonding Much weaker forces but strong enough to influence behavior of liquids

81. Properties of Liquids and Solids The solid state is predominated by potential energy rather than by kinetic energy Particles are in a fixed position by strong electrostatic attractions but vibrate due to kinetic energy Definite volume and shape High density: the particles are located as close as possible

82. Properties of Liquids and Solids In the liquid state is not dominated by potential energy or by kinetic energy Particles are in not in a fixed position due to kinetic energy and can slide over each other The potential energy (cohesive force) is strong enough prevent total separation Assumes the shape of the container it occupies Definite volume and indefinite shape High density: the particles are not widely separated but located as close as possible

83. Properties of Liquids and Solids In the gaseous state is dominated completely by kinetic energy Particles of a gas are independent of each other and move in a totally random manner due to their kinetic energy The attractive forces between particles have been overcome by kinetic energy which allows particles to travel in all directions Assumes both the volume and shape of the container it occupies Indefinite volume and indefinite shape Low density: the particles are widely separated and relatively few particles per unit volume

84. Properties of Liquids and Solids Liquid and solid phases have many similar characteristics but gases are very different The average distance between the particles only slightly different in the solid and liquid but vastly different in the gaseous state

85. Surface Tension and Viscosity In a liquid, surface tension arises when molecules on the surface act like a thin membrane that allows objects to move on the surface liquid Due to forces of attraction that bind them across the surface and pull them into the body of the liquid This inward force causes the surface to contract to as small a surface as possible Unlike the molecules within the body of the liquid that experience forces equally in all directions

86. Surface Tension and Viscosity Surface tension results from an imbalance in forces of attraction The magnitude of the surface tension of a liquid is affected by the strength of its intermolecular forces Water has strong intermolecular forces and thus, very high surface tension

87. Surface Tension and Viscosity Since liquids are incompressible and can flow, they assume the shape of their container Some liquids easily flow and others do not (e.g. water vs. molasses) Viscosity is a measure of a fluid’s resistance to flow The stronger the intermolecular forces, the greater the resistance to flow

88. Attractive Forces in Compounds Intermolecular Forces Intermolecular Forces Ionic compounds: Ions (+ and -) are held together by ionic bondsIonic compounds: Ions (+ and -) are held together by ionic bonds Neutral molecules: One or more of these forces hold molecules together in liquids and solids:Neutral molecules: One or more of these forces hold molecules together in liquids and solids: Dipole-dipoleDipole-dipole Hydrogen-bondingHydrogen-bonding DispersionDispersion

89. Attractive Forces in Compounds Dipole-dipole: Attractions between polar molecules Dipole-dipole: Attractions between polar molecules The nonsymmetrical distribution of the charge causes the molecules to line up The nonsymmetrical distribution of the charge causes the molecules to line up Positive end of one directed toward negative end of other Positive end of one directed toward negative end of other

90. Attractive Forces in Compounds Hydrogen bonding: A special type of dipole- dipole interaction Hydrogen bonding: A special type of dipole- dipole interaction Occurs between molecules that have a H atom bonded to F, O, or N Occurs between molecules that have a H atom bonded to F, O, or N The partially positive H and a lone pair of electrons on another N, O, or F atom The partially positive H and a lone pair of electrons on another N, O, or F atom

91. Attractive Forces in Compounds Dispersion (London) forces: Short-lived dipoles caused by uneven shifts in electron density Dispersion (London) forces: Short-lived dipoles caused by uneven shifts in electron density The uneven shift causes one end of the molecule to be slightly positive and one end slightly negative The uneven shift causes one end of the molecule to be slightly positive and one end slightly negative This induces the same electron shift in adjacent molecules which causes an attractive force This induces the same electron shift in adjacent molecules which causes an attractive force Only intermolecular force possible in nonpolar substances Only intermolecular force possible in nonpolar substances

92. Matter and Changes of State Matter: Anything that has mass and occupies space Matter: Anything that has mass and occupies space It is separated into three categories: Solid, Liquid, and Gas It is separated into three categories: Solid, Liquid, and Gas

93. Matter and Changes of State A change in state is the most common type of physical change A change in state is the most common type of physical change Melting/FreezingMelting/Freezing Vaporization/CondensationVaporization/Condensation Sublimation/DepositionSublimation/Deposition The composition of the substance does not change, only its appearance The composition of the substance does not change, only its appearance

94. Melting/Freezing A change of state requiring the input of heat A change of state requiring the input of heat Heat of Fusion Heat of Fusion Heat energy required to melt 1 g of a substanceHeat energy required to melt 1 g of a substance Heat energy that must be removed to freeze 1 g of a substanceHeat energy that must be removed to freeze 1 g of a substance Heat energy (to melt) 1 g of ice (water at 0 °C):Heat energy (to melt) 1 g of ice (water at 0 °C):

95. Change of State Problem Calculate the heat needed (in Joules) to melt 15 g of ice at 0°C, and to heat the water to 75 °C Calculate the heat needed (in Joules) to melt 15 g of ice at 0°C, and to heat the water to 75 °C Two parts to the problem Two parts to the problem Melt ice (use heat of fusion for water)Melt ice (use heat of fusion for water) Heat water (use specific heat of Water)Heat water (use specific heat of Water)

96. Change of State Problem Melt the ice Melt the ice Calculate the heat absorbed to melt the ice at 0 °C (no change in temperature) Calculate the heat absorbed to melt the ice at 0 °C (no change in temperature)

97. Change of State Problem Heat the water Heat the water Calculate the heat energy needed to warm the water from 0 °C to 75 °C Calculate the heat energy needed to warm the water from 0 °C to 75 °C (75 °C)

98. Change of State Problem Combining Energy Calculations Calculate the total heat Calculate the total heat Melting the ice (Q 1 )Melting the ice (Q 1 ) Heating the water (Q 2Heating the water (Q 2 )

99. Change of State Sublimation: A phase change from solid to gas without going through the liquid state Sublimation: A phase change from solid to gas without going through the liquid state Requires the absorption of heatRequires the absorption of heat No temperature change occurs during processNo temperature change occurs during process Deposition is the reverse process (heat is released)Deposition is the reverse process (heat is released) Evaporation: A phase change from a liquid to a gas Evaporation: A phase change from a liquid to a gas Requires the absorption of heatRequires the absorption of heat No temperature change occurs during processNo temperature change occurs during process Condensation is the reverse process (heat is released)Condensation is the reverse process (heat is released)

100. Change of State Boiling: A special form of evaporation where the liquid converts to vapor through bubble formation Boiling: A special form of evaporation where the liquid converts to vapor through bubble formation Boiling point: Temp at which the vapor pressure of the liquid is the same as the atmospheric pressure Boiling point: Temp at which the vapor pressure of the liquid is the same as the atmospheric pressure This allows the bubbles at the liquid surface to escape in the atmosphere This allows the bubbles at the liquid surface to escape in the atmosphere

101. Vaporization/Condensation Heat of Vaporization Heat of Vaporization Heat energy required to vaporize 1 g of a substanceHeat energy required to vaporize 1 g of a substance Heat energy that must be removed to condense 1 g of a substanceHeat energy that must be removed to condense 1 g of a substance Heat energy (to vaporize) 1 g of water to vapor:Heat energy (to vaporize) 1 g of water to vapor:

102. Change of State Problem Calculate the heat needed (in Joules) to heat 15 g of water from 75 °C to 100 °C, and to convert it to steam at 100 °C Two parts to the problem Two parts to the problem Heat the water (use specific heat for water)Heat the water (use specific heat for water) Convert water to steam (use heat of vaporization for Water)Convert water to steam (use heat of vaporization for Water)

103. Change of State Problem Heat the water Heat the water Calculate the heat energy needed to warm the water from 75 °C to 100 °C Calculate the heat energy needed to warm the water from 75 °C to 100 °C ×25 °C

104. Change of State Problem Calculate the heat absorbed to convert the liquid water to steam at 100 °C (no change in temperature) Calculate the heat absorbed to convert the liquid water to steam at 100 °C (no change in temperature)

105. Change of State Problem Combining Energy Calculations Calculate the total heat Calculate the total heat Heat the water (Q 1 )Heat the water (Q 1 ) Convert liquid water to steam (Q 2Convert liquid water to steam (Q 2 )

106. Heats of Fusion and Vaporization

107. Heating Curve Illustrates the steps involved in changing a solid to a gas Illustrates the steps involved in changing a solid to a gas Heat added is shown on the x-axisHeat added is shown on the x-axis Temperature is shown on the y-axisTemperature is shown on the y-axis Energy required to undergo a series of phase changes depends on the (three) property values of the substance: Energy required to undergo a series of phase changes depends on the (three) property values of the substance: Specific HeatSpecific Heat Heat of FusionHeat of Fusion Heat of VaporizationHeat of Vaporization

108. Heating Curve No temp change No temp change

109. end end

110. Sharing Electrons Between Atoms of Different Elements Two nonidentical nonmetal atoms Two nonidentical nonmetal atoms The number of covalent bonds an atom forms will equal the number of electrons needed to form a noble gas configuration The number of covalent bonds an atom forms will equal the number of electrons needed to form a noble gas configuration Each vacancy + unpaired electron combination in the valence shell can be used to form a two- electron bond Each vacancy + unpaired electron combination in the valence shell can be used to form a two- electron bond Each atom will share valence electrons with the other forming a shared pair of bonding electrons (achieves a stable noble gas configuration) Each atom will share valence electrons with the other forming a shared pair of bonding electrons (achieves a stable noble gas configuration)

111. Covalent Lewis Structures: Double and Triple Bonds Bonding Single Bond Single Bond Uses a single pair of electrons between two atomsUses a single pair of electrons between two atoms Double Bond Double Bond Uses two pairs of electrons between the same two atomsUses two pairs of electrons between the same two atoms Triple Bond Triple Bond Uses three pairs of electrons between the same two atomsUses three pairs of electrons between the same two atoms

112. Writing Resonance Structures Example: Write a Lewis structure for nitrate ion and include resonance structures Example: Write a Lewis structure for nitrate ion and include resonance structures Use a double-headed arrow to connect the structures Use a double-headed arrow to connect the structures

113. Lewis Structures for Ionic Compounds: Electrons Transferred The reaction of sodium and chlorine The reaction of sodium and chlorine The reaction represented through dot structures: The reaction represented through dot structures: Na + :Cl: Li 1+ [:F:] 1-

114. Resonance Resonance occurs whenever it is possible to draw two or more electron- dot structures Resonance occurs whenever it is possible to draw two or more electron- dot structures They differ only in the location of a double bond between the same two types of atoms They differ only in the location of a double bond between the same two types of atoms Two of the four electrons in the double bond rapidly move between the two single bonds: The true structure is the average of the individual structures Two of the four electrons in the double bond rapidly move between the two single bonds: The true structure is the average of the individual structures