Copyright© The McGraw-Hill Companies, Inc. Permission required for reproduction or display.              Chapter 3        ...
3.1 Chemical Bonding• Chemical bond - the force of attraction  between any two atoms in a compound• This attractive force ...
3.1 Chemical Bonding              Lewis Symbols                       • Lewis symbol (Lewis structure) - a way to         ...
3.1 Chemical Bonding                  Lewis Symbols                       • Each “side” of the symbol represents an atomic...
3.1 Chemical Bonding   Lewis Dot Symbols for                       Representative Elements
Principal Types of Chemical Bonds:                                Ionic and Covalent3.1 Chemical Bonding                  ...
3.1 Chemical Bonding               Ionic Bonding                       • Representative elements form ions that           ...
3.1 Chemical Bonding                 Ionic Bonding                        Consider the formation of                       ...
Essential Features of Ionic Bonding3.1 Chemical Bonding                       • Atoms with low I.E. and low E.A. tend to f...
3.1 Chemical Bonding      Ion Arrangement in a Crystal                       • As a sodium atom loses one electron, it bec...
3.1 Chemical Bonding             Covalent Bonding                       Let’s look at the formation of H2:                ...
3.1 Chemical Bonding                       • Instead, each atom attains a noble gas                         configuration ...
3.1 Chemical Bonding   Covalent Bonding in Hydrogen
3.1 Chemical Bonding       Features of Covalent Bonds                       • Covalent bonds form between atoms with      ...
3.1 Chemical Bonding   Examples of Covalent Bonding                                   ..       ..                         ...
Polar Covalent Bonding and                                Electronegativity3.1 Chemical Bonding                       • Th...
somewhat positively charged   somewhat negatively charged3.1 Chemical Bonding                          ..      ..         ...
3.1 Chemical Bonding   Polar Covalent Bonding in Water                       • Oxygen is electron rich = δ-               ...
3.1 Chemical Bonding              Electronegativity                       • Electronegativity - a measure of the          ...
Electronegativities of Selected                                   Elements3.1 Chemical Bonding                       • The...
3.1 Chemical Bonding     Electronegativity Calculations                       • The greater the difference in electronegat...
3.2 Naming Compounds and  Writing Formulas of Compounds• Nomenclature - the assignment of a correct  and unambiguous name ...
3.2 Naming Compounds and                                      Formulas of Compounds                           Writing Form...
3.2 Naming Compounds and                                             Ionic Compounds                           Writing For...
3.2 Naming Compounds and                                     Writing Formulas of Ionic Compounds                          ...
3.2 Naming Compounds and                                           Predict Formulas                           Writing Form...
3.2 Naming Compounds and                                   Writing Names of Ionic Compounds                           Writ...
3.2 Naming Compounds and                                       Writing Names of Ionic Compounds                           ...
3.2 Naming Compounds and                           Writing Formulas of Compounds   Common Nomenclature System             ...
3.2 Naming Compounds andWriting Formulas of Compounds                          Iron and Copper Ions                      S...
3.2 Naming Compounds and                           Writing Formulas of Compounds   Common Monatomic Cations               ...
3.2 Naming Compounds and                                               Polyatomic Ions                           Writing F...
3.2 Naming Compounds andWriting Formulas of Compounds     Anions                        Common Polyatomic Cations and
3.2 Naming Compounds and                           Writing Formulas of Compounds      Name These Compounds                ...
3.2 Naming Compounds and                        Writing Formulas of Ionic Compounds                           Writing Form...
3.2 Naming Compounds and                                   Determine the Formulas From                           Writing F...
3.2 Naming Compounds and                                         Covalent Compounds                           Writing Form...
3.2 Naming Compounds and                           Writing Formulas of Compounds   Naming Covalent Compounds              ...
3.2 Naming Compounds and                                   Naming Covalent Compounds                           Writing For...
3.2 Naming Compounds and                               Name These Covalent Compounds                       Writing Formula...
3.2 Naming Compounds and                                   Writing Formulas of Covalent                           Writing ...
3.2 Naming Compounds and                                 Provide Formulas for These                       Writing Formulas...
3.3 Properties of Ionic and         Covalent Compounds• Physical State  – Ionic compounds are usually solids at room    te...
Physical Properties3.3 Properties of Ionic and  Covalent Compounds                              • Melting and Boiling Poin...
Physical Properties3.3 Properties of Ionic and  Covalent Compounds                              • Solutions of Ionic and C...
Comparison of Ionic vs. Covalent          Compounds                 Ionic               CovalentComposed of      Metal + n...
3.4 Drawing Lewis Structures on    Molecules and Polyatomic IonsLewis Structure Guidelines1. Use chemical symbols for the ...
Structures of Molecules      Lewis Structure Guidelines                          2. Determine the number of valence  3.4 D...
Structures of Molecules      Lewis Structure Guidelines                          3. Connect the central atom to each of th...
Lewis Structure GuidelinesStructures of Molecules                          4. Count the number of electrons you have  3.4 ...
Structures of Molecules   Drawing Lewis Structures of                             Covalent Compounds  3.4 Drawing Lewis   ...
Structures of Molecules        Drawing Lewis Structures  3.4 Drawing Lewis                          5. Find the number of ...
Drawing Lewis Structures ofStructures of Molecules           Covalent Compounds  3.4 Drawing Lewis                        ...
Lewis Structures PracticeStructures of Molecules                          Using the guidelines presented, write Lewis  3.4...
Lewis Structures ofStructures of Molecules                                 Polyatomic Ions                  6  3.4 Drawing...
Lewis Structure ofStructures of Molecules             Polyatomic Cations  3.4 Drawing Lewis                          Draw ...
Lewis Structure of PolyatomicStructures of Molecules              Anions  3.4 Drawing Lewis                          Draw ...
Lewis Structure of PolyatomicStructures of Molecules              Anions  3.4 Drawing Lewis                          Draw ...
Lewis Structure, Stability, Multiple                    Bonds, and Bond EnergiesStructures of Molecules  3.4 Drawing Lewis...
.. ..                          H : H or H - H         O :: O or O = OStructures of Molecules                          ⋅⋅ ⋅...
Lewis Structures and ResonanceStructures of Molecules                          • Write the Lewis structure of CO32-  3.4 D...
..                               ..                               :O:             :O:              :O:Structures of Molecu...
Lewis Structures and ExceptionsStructures of Molecules          to the Octet Rule  3.4 Drawing Lewis                      ...
Structures of Molecules                   Odd Electron                          2. Odd electron - if there is an odd numbe...
Structures of Molecules                   Expanded Octet  3.4 Drawing Lewis                          3.   Expanded octet -...
Structures of Molecules   Lewis Structures and Molecular                            Geometry: VSEPR Theory  3.4 Drawing Le...
Structures of Molecules            VSEPR Theory  3.4 Drawing Lewis                          • In the covalent bond, bondin...
Structures of Molecules            Molecular Bonding  3.4 Drawing Lewis                          • Bonding pair = two elec...
3.4 Molecular Geometry    A Stable Exception to the Octet                                      Rule                       ...
3.4 Molecular Geometry    Another Stable Exception to the                                    Octet Rule                   ...
3.4 Molecular Geometry   Basic Electron Pair Repulsion of                                   a Full Octet                  ...
3.4 Molecular Geometry     Basic Electron Pair Repulsion of                           a Full Octet with One Lone Pair     ...
3.4 Molecular Geometry    Basic Electron Pair Repulsion of                          a Full Octet with Two Lone Pairs      ...
Predicting Geometric Shape UsingStructures of Molecules             Electron Pairs  3.4 Drawing Lewis
Basic Procedure to DetermineStructures of Molecules         Molecular Shape  3.4 Drawing Lewis                          1....
Determine the MolecularStructures of Molecules                                   Geometry  3.4 Drawing Lewis              ...
Lewis Structures and PolarityStructures of Molecules                          • A molecule is polar if its centers of posi...
Structures of Molecules             Determining Polarity                          To determine if a molecule is polar:  3....
Practice Determining PolarityStructures of Molecules                          Determine whether the following bonds and  3...
3.5 Properties Based on ElectronicStructure and Molecular Geometry• Intramolecular forces – attractive forces  within mole...
Solubility and IntermolecularStructure and Molecular Geometry3.5 Properties Based on Electronic                           ...
Interaction of Water andStructure and Molecular Geometry3.5 Properties Based on Electronic                                ...
Structure and Molecular Geometry3.5 Properties Based on Electronic                                         Interaction of ...
Boiling Points of LiquidsStructure and Molecular Geometry3.5 Properties Based on Electronic                               ...
Factors Influencing Boiling andStructure and Molecular Geometry3.5 Properties Based on Electronic                         ...
3.5 Properties Based on ElectronicStructure and Molecular Geometry                                                        ...
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  1. 1. Copyright© The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Structure and Properties of Ionic and Covalent CompoundsDennistonToppingCaret7th Edition
  2. 2. 3.1 Chemical Bonding• Chemical bond - the force of attraction between any two atoms in a compound• This attractive force overcomes the repulsion of the positively charged nuclei of the two atoms participating in the bond• Interactions involving valence electrons are responsible for the chemical bond
  3. 3. 3.1 Chemical Bonding Lewis Symbols • Lewis symbol (Lewis structure) - a way to represent atoms using the element symbol and valence electrons as dots • As only valence electrons participate in bonding, this makes it much easier to work with the octet rule • The number of dots used corresponds directly to the number of valence electrons located in the outermost shell of the atoms of the element
  4. 4. 3.1 Chemical Bonding Lewis Symbols • Each “side” of the symbol represents an atomic orbital, which may hold up to two electrons • Using Lewis symbols – Place one dot on each side until there are four dots around the symbol – Now add a second dot to each side in turn – The number of valence electrons limits the number of dots placed – Each unpaired dot (unpaired electron of the valence shell) is available to form a chemical bond
  5. 5. 3.1 Chemical Bonding Lewis Dot Symbols for Representative Elements
  6. 6. Principal Types of Chemical Bonds: Ionic and Covalent3.1 Chemical Bonding • Ionic bond - a transfer of one or more electrons from one atom to another • Forms attractions due to the opposite charges of the atoms • Covalent bond - attractive force due to the sharing of electrons between atoms • Some bonds have characteristics of both types and not easily identified as one or the other
  7. 7. 3.1 Chemical Bonding Ionic Bonding • Representative elements form ions that obey the octet rule • Ions of opposite charge attract each other creating the ionic bond • When electrons are lost by a metal and electrons are gained by a nonmetal – Each atom achieves a “Noble Gas” configuration – 2 ions are formed; a cation and anion, which are attracted to each other
  8. 8. 3.1 Chemical Bonding Ionic Bonding Consider the formation of NaCl Chlorine has a high Na + Cl  NaCl electron affinity When chlorine gains Sodium has a low an electron, it gains ionization energy it the Ar configuration readily loses this electron .. −  ..  − : Cl⋅ + e → : Cl : Na  Na+ + e- ..  ..  When sodium loses the electron, it gains the Ne configuration
  9. 9. Essential Features of Ionic Bonding3.1 Chemical Bonding • Atoms with low I.E. and low E.A. tend to form positive ions • Atoms with high I.E. and high E.A. tend to form negative ions • Ion formation takes place by electron transfer • The ions are held together by the electrostatic force of the opposite charges • Reactions between metals and nonmetals (representative elements) tend to be ionic
  10. 10. 3.1 Chemical Bonding Ion Arrangement in a Crystal • As a sodium atom loses one electron, it becomes a smaller sodium ion • When a chlorine atom gains that electron, it becomes a larger chloride ion • Attraction of the Na cation with the Cl anion forms NaCl ion pairs that aggregate into a crystal
  11. 11. 3.1 Chemical Bonding Covalent Bonding Let’s look at the formation of H2: H + H  H2 • Each hydrogen has one electron in its valance shell • If it were an ionic bond it would look like this: H ⋅ + H ⋅ → H + [ H :] + − • However, both hydrogen atoms have an equal tendency to gain or lose electrons • Electron transfer from one H to another usually will not occur under normal conditions
  12. 12. 3.1 Chemical Bonding • Instead, each atom attains a noble gas configuration by sharing electrons H⋅ + ⋅H →H : H Each hydrogen atom now has two The shared electrons around it electron and attained a He pair is called a configuration Covalent Bond
  13. 13. 3.1 Chemical Bonding Covalent Bonding in Hydrogen
  14. 14. 3.1 Chemical Bonding Features of Covalent Bonds • Covalent bonds form between atoms with similar tendencies to gain or lose electrons • Compounds containing covalent bonds are called covalent compounds or molecules • The diatomic elements have completely covalent bonds (totally equal sharing) – H2, N2, O2, F2, Cl2, Br2, I2 Each fluorine is .. .. .. .. surrounded by 8 : F⋅ + ⋅ F : → : F : F : electrons – Ne .. .. .. .. configuration
  15. 15. 3.1 Chemical Bonding Examples of Covalent Bonding .. .. 2H ⋅ + ⋅ O⋅ → H : O : H .. .. 2e– from 2H 2e– for H 6e– from O 8e– for O H . .. 4H ⋅ + ⋅ C⋅ → H : C : H ⋅ ⋅⋅ H 4e– from 4H 2e– for H 4e– from C 8e– for C
  16. 16. Polar Covalent Bonding and Electronegativity3.1 Chemical Bonding • The Polar Covalent Bond – Ionic bonding involves the transfer of electrons – Covalent bonding involves the sharing of electrons – Polar covalent bonding - bonds made up of unequally shared electron pairs
  17. 17. somewhat positively charged somewhat negatively charged3.1 Chemical Bonding .. .. H⋅ + ⋅F:→ H : F: ⋅⋅ ⋅⋅ These two electrons are not shared equally • The electrons spend more time with fluorine • This sets up a polar covalent bond • A truly covalent bond can only occur when both atoms are identical
  18. 18. 3.1 Chemical Bonding Polar Covalent Bonding in Water • Oxygen is electron rich = δ- • Hydrogen is electron deficient = δ+ • This results in unequal sharing of electrons in the pairs = polar covalent bonds • Water has 2 covalent bonds
  19. 19. 3.1 Chemical Bonding Electronegativity • Electronegativity - a measure of the ability of an atom to attract electrons in a chemical bond • Elements with high electronegativity have a greater ability to attract electrons than do elements with low electronegativity • Consider the covalent bond as competition for electrons between 2 positive centers – The difference in electronegativity determines the extent of bond polarity
  20. 20. Electronegativities of Selected Elements3.1 Chemical Bonding • The most electronegative elements are found in the upper right corner of the periodic table • The least electronegative elements are found in the lower left corner of the periodic table electronegativity increases electronegativity increases
  21. 21. 3.1 Chemical Bonding Electronegativity Calculations • The greater the difference in electronegativity between two atoms, the greater the polarity of their bond • Which would be more polar, a H-F bond or H-Cl bond? • H-F … 4.0 - 2.1 = 1.9 • H-Cl … 3.0 - 2.1 = 0.9 • The HF bond is more polar than the HCl bond
  22. 22. 3.2 Naming Compounds and Writing Formulas of Compounds• Nomenclature - the assignment of a correct and unambiguous name to each and every chemical compound• Two naming systems: – ionic compounds – covalent compounds
  23. 23. 3.2 Naming Compounds and Formulas of Compounds Writing Formulas of Compounds • A formula is the representation of the fundamental compound using chemical symbols and numerical subscripts – The formula identifies the number and type of the various atoms that make up the compound unit – The number of like atoms in the unit is shown by the use of a subscript – Presence of only one atom is understood when no subscript is present
  24. 24. 3.2 Naming Compounds and Ionic Compounds Writing Formulas of Compounds • Metals and nonmetals usually react to form ionic compounds • The metals are cations and the nonmetals are anions • The cations and anions arrange themselves in a regular three-dimensional repeating array called a crystal lattice • Formula of an ionic compound is the smallest whole-number ratio of ions in the substance
  25. 25. 3.2 Naming Compounds and Writing Formulas of Ionic Compounds Writing Formulas of Compounds from the Identities of the Component Ions • Determine the charge of each ion – Metals have a charge equal to group number – Nonmetals have a charge equal to the group number minus eight • Cations and anions must combine to give a formula with a net charge of zero • It must have the same number of positive charges as negative charges
  26. 26. 3.2 Naming Compounds and Predict Formulas Writing Formulas of Compounds Predict the formula of the ionic compounds formed from combining ions of the following pairs of elements: 1. sodium and oxygen 2. lithium and bromine 3. aluminum and oxygen 4. barium and fluorine
  27. 27. 3.2 Naming Compounds and Writing Names of Ionic Compounds Writing Formulas of Compounds from the Formula of the Compound • Name the cation followed by the name2 of the anion • A positive ion retains the name of the element; change the anion suffix to -ide
  28. 28. 3.2 Naming Compounds and Writing Names of Ionic Compounds Writing Formulas of Compounds from the Formula of the Compound • If the cation of an element has several ions of different charges (as with transition metals) use a Roman numeral following the metal name • Roman numerals give the charge of the metal • Examples: • FeCl3 is iron(III) chloride • FeCl2 is iron(II) chloride • CuO is copper(II) oxide
  29. 29. 3.2 Naming Compounds and Writing Formulas of Compounds Common Nomenclature System • Use -ic to indicate the higher of the charges that ion might have • Use -ous to indicate the lower of the charges that ion might have • Examples: • FeCl2 is ferrous chloride • FeCl3 is ferric chloride
  30. 30. 3.2 Naming Compounds andWriting Formulas of Compounds Iron and Copper Ions Stock and Common Names for
  31. 31. 3.2 Naming Compounds and Writing Formulas of Compounds Common Monatomic Cations and Anions • Monatomic ions - ions consisting of a single charged atom
  32. 32. 3.2 Naming Compounds and Polyatomic Ions Writing Formulas of Compounds • Polyatomic ions - ions composed of 2 or more atoms bonded together with an overall positive or negative charge – Within the ion itself, the atoms are bonded using covalent bonds – The positive and negative ions will be bonded to each other with ionic bonds • Examples: • NH4+ ammonium ion • SO42- sulfate ion
  33. 33. 3.2 Naming Compounds andWriting Formulas of Compounds Anions Common Polyatomic Cations and
  34. 34. 3.2 Naming Compounds and Writing Formulas of Compounds Name These Compounds 1. NH4Cl 2. BaSO4 3. Fe(NO3)3 4. CuHCO3 5. Ca(OH)2
  35. 35. 3.2 Naming Compounds and Writing Formulas of Ionic Compounds Writing Formulas of Compounds From the Name of the Compound • Determine the charge of each ion • Write the formula so that the resulting compound is neutral • Example: Barium chloride: Barium is +2, Chloride is -1 Formula is BaCl2
  36. 36. 3.2 Naming Compounds and Determine the Formulas From Writing Formulas of Compounds Names Write the formula for the following ionic compounds: 1. sodium sulfate 2. ammonium sulfide 3. magnesium phosphate 4. chromium(II) sulfate
  37. 37. 3.2 Naming Compounds and Covalent Compounds Writing Formulas of Compounds • Covalent compounds are typically formed from nonmetals • Molecules - compounds characterized by covalent bonding • Not a part of a massive three-dimensional crystal structure • Exist as discrete molecules in the solid, liquid, and gas states
  38. 38. 3.2 Naming Compounds and Writing Formulas of Compounds Naming Covalent Compounds 1. The names of the elements are written in the order in which they appear in the formula 2. A prefix indicates the number of each kind of atom
  39. 39. 3.2 Naming Compounds and Naming Covalent Compounds Writing Formulas of Compounds 3. If only one atom of a particular element is present in the molecule, the prefix mono- is usually omitted from the first element Example: CO is carbon monoxide 4. The stem of the name of the last element is used with the suffix –ide 5. The final vowel in a prefix is often dropped before a vowel in the stem name
  40. 40. 3.2 Naming Compounds and Name These Covalent Compounds Writing Formulas of Compounds 1. SiO2 2. N2O5 3. CCl4 4. IF7
  41. 41. 3.2 Naming Compounds and Writing Formulas of Covalent Writing Formulas of Compounds Compounds • Use the prefixes in the names to determine the 2 subscripts for the elements • Examples: • nitrogen trichloride NCl3 • diphosphorus pentoxide P2O5 • Some common names that are used: – H2O water – NH3 ammonia – C2H5OH ethanol – C6H12O6 glucose
  42. 42. 3.2 Naming Compounds and Provide Formulas for These Writing Formulas of Compounds Covalent Compounds 1. nitrogen monoxide 2. dinitrogen tetroxide 3. diphosphorus pentoxide 4. nitrogen trifluoride
  43. 43. 3.3 Properties of Ionic and Covalent Compounds• Physical State – Ionic compounds are usually solids at room temperature – Covalent compounds can be solids, liquids, and gases• Melting and Boiling Points – Melting point - the temperature at which a solid is converted to a liquid – Boiling point - the temperature at which a liquid is converted to a gas
  44. 44. Physical Properties3.3 Properties of Ionic and Covalent Compounds • Melting and Boiling Points – Ionic compounds have much higher melting points and boiling points than covalent compounds – A large amount of energy is required to break the electrostatic attractions between ions – Ionic compounds typically melt at several hundred degrees Celsius • Structure of Compounds in the Solid State – Ionic compounds are crystalline – Covalent compounds are crystalline or amorphous – having no regular structure
  45. 45. Physical Properties3.3 Properties of Ionic and Covalent Compounds • Solutions of Ionic and Covalent Compounds – Ionic compounds often dissolve in water, where they dissociate - form positive and negative ions in solution – Electrolytes - ions present in solution allowing the solution to conduct electricity – Covalent solids usually do not dissociate and do not conduct electricity - nonelectrolytes
  46. 46. Comparison of Ionic vs. Covalent Compounds Ionic CovalentComposed of Metal + nonmetal 2 nonmetalsElectrons Transferred SharedPhysical state Solid / crystal Any / crystal OR amorphousDissociation Yes, electrolytes No, nonelectrolytesBoiling/Melting High Low
  47. 47. 3.4 Drawing Lewis Structures on Molecules and Polyatomic IonsLewis Structure Guidelines1. Use chemical symbols for the various elements to write the skeletal structure of the compound – The least electronegative atom will be placed in the central position – Hydrogen and halogens occupy terminal positions – Carbon often forms chains of carbon-carbon covalent bonds
  48. 48. Structures of Molecules Lewis Structure Guidelines 2. Determine the number of valence 3.4 Drawing Lewis electrons associated with each atom in the compound – Combine these valence electrons to determine the total number of valence electrons in the compound – Polyatomic cations, subtract one electron for every positive charge – Polyatomic anions, add one electron for every negative charge
  49. 49. Structures of Molecules Lewis Structure Guidelines 3. Connect the central atom to each of the 3.4 Drawing Lewis surrounding atoms using electron pairs • Next, complete octets of all the atoms bonded to the central atom • Hydrogen needs only two electrons • Electrons not involved in bonding are represented as lone pairs • Total number of electrons in the structure must equal the number of valence electrons in step 2
  50. 50. Lewis Structure GuidelinesStructures of Molecules 4. Count the number of electrons you have 3.4 Drawing Lewis and compare to the number you used • If they are the same, you are finished • If you used more electrons than you have, add a bond for every two too many you used • Then, give every atom an octet • If you used less electrons than you have….see later exceptions to the octet rule 5. Recheck that all atoms have the octet rule satisfied and that the total number of valance electrons are used
  51. 51. Structures of Molecules Drawing Lewis Structures of Covalent Compounds 3.4 Drawing Lewis Draw the Lewis structure of carbon dioxide, CO2 Draw a skeletal structure of the molecule 1. Arrange the atoms in their most probable order C-O-O and/or O-C-O 2. Find the electronegativity of O=3.5 & C=2.5 3. Place the least electronegative atom as the central atom, here carbon is the central atom 4. Result is the O-C-O structure from above
  52. 52. Structures of Molecules Drawing Lewis Structures 3.4 Drawing Lewis 5. Find the number of valence electrons for each atom and the total for the compound 1 C atom x 4 valence electrons = 4 e- 2 O atoms x 6 valence electrons = 12 e- 16 e- total 6. Use electron pairs to connect the C to each O with a single bond O:C:O 7. Place electron pairs around the atoms : : : : :O:C:O: This satisfies the rule for the O atoms, but not for C
  53. 53. Drawing Lewis Structures ofStructures of Molecules Covalent Compounds 3.4 Drawing Lewis 8. Redistribute the electrons moving 2 e- from each O, placing them between C:O : : : : C::O::C 9. In this structure, the octet rule is satisfied • This is the most probable structure • Four electrons are between C and O • These electrons are share in covalent bonds • Four electrons in this arrangement signify a double bond 10. Recheck the electron distribution • 8 electron pairs = 16 valence electrons, number counted at start • 8 electrons around each atom, octet rule satisfied
  54. 54. Lewis Structures PracticeStructures of Molecules Using the guidelines presented, write Lewis 3.4 Drawing Lewis structures for the following: 1. H2O 2. NH3 3. CO2 4. NH4+ 5. CO32- 6. N2
  55. 55. Lewis Structures ofStructures of Molecules Polyatomic Ions 6 3.4 Drawing Lewis • Prepare Lewis structures of polyatomic ions as for neutral compounds, except: • The charge on the ion must be accounted for when computing the total number of valence electrons
  56. 56. Lewis Structure ofStructures of Molecules Polyatomic Cations 3.4 Drawing Lewis Draw the Lewis structure of ammonium ion, NH4+ Draw a skeletal structure of the molecule 1. Ammonium has this structure and charge: 2. The total number of valence electrons is determined by subtracting one electron for each unit of positive charge 1 N atom x 5 valence electrons = 5 e- 4 H atoms x 1 valence electron = 4 e- - 1 electron for +1 charge = -1 e- 8 e- total 3. Distribute these 8 e- around the skeletal structure
  57. 57. Lewis Structure of PolyatomicStructures of Molecules Anions 3.4 Drawing Lewis Draw the Lewis structure of carbonate ion, CO32- Draw a skeletal structure of the molecule 1. Carbon is less electronegative than oxygen • This makes carbon the central atom • Skeletal structure and charge: 2. The total number of valence electrons is determined by adding one electron for each unit of negative charge 1 C atom x 4 valence electrons = 4 e- 3 O atoms x 6 valence electron = 18 e- + 2 negative charges = 2 e- 24 e- total 3. Distribute these e- around the skeletal structure
  58. 58. Lewis Structure of PolyatomicStructures of Molecules Anions 3.4 Drawing Lewis Draw the Lewis structure of carbonate ion, CO32- 4. Distributing the electrons around the central carbon atom (4 bonds) and around the surrounding O atoms attempting to satisfy the octet rule results in: 5. This satisfies the octet rule for the 3 oxygen, but not for the carbon 6. Move a lone pair from one of the O atoms to form another bond with C
  59. 59. Lewis Structure, Stability, Multiple Bonds, and Bond EnergiesStructures of Molecules 3.4 Drawing Lewis • Single bond - one pair of electrons are shared between two atoms • Double bond - two pairs of electrons are shared between two atoms • Triple bond - three pairs of electrons are shared between two atoms • Very stable
  60. 60. .. .. H : H or H - H O :: O or O = OStructures of Molecules ⋅⋅ ⋅⋅ .. .. 3.4 Drawing Lewis N  N or N ≡ N Bond energy - the amount of energy required to break a bond holding two atoms together triple bond > double bond > single bond Bond length - the distance separating the nuclei of two adjacent atoms single bond > double bond > triple bond
  61. 61. Lewis Structures and ResonanceStructures of Molecules • Write the Lewis structure of CO32- 3.4 Drawing Lewis • If you look around you, you will probably see the double bond put in different places • Who is right? All of you! • In some cases it is possible to write more than one Lewis structure that satisfies the octet rule for a particular compound
  62. 62. .. .. :O: :O: :O:Structures of Molecules : :: : .. .. .. .. .. : O : C :: O ↔ : O : C : O : ↔ : O :: C : O : 3.4 Drawing Lewis ⋅⋅ ⋅⋅ ⋅⋅ ⋅⋅ • Experimental evidence shows all bonds are the same length, meaning there is not really any double bond in this ion • None of theses three Lewis structures exist, but the actual structure is an average or hybrid of these three Lewis structures • Resonance - two or more Lewis structures that contribute to the real structure
  63. 63. Lewis Structures and ExceptionsStructures of Molecules to the Octet Rule 3.4 Drawing Lewis 1. Incomplete octet - less then eight electrons around an atom other than H – Let’s look at BeH2 1 Be atom x 2 valence electrons = 2 e- 2 H atoms x 1 valence electrons = 2 e- total 4 e- – Resulting Lewis structure: H : Be : H or H – Be – H
  64. 64. Structures of Molecules Odd Electron 2. Odd electron - if there is an odd number of 3.4 Drawing Lewis valence electrons, it is not possible to give every atom eight electrons • Let’s look at NO, nitric oxide • It is impossible to pair all electrons as the compound contains an ODD number of valence electrons N - O
  65. 65. Structures of Molecules Expanded Octet 3.4 Drawing Lewis 3. Expanded octet - an element in the 3rd period or below may have 10 and 12 electrons around it • Expanded octet is the most common exception • Consider the Lewis structure of PF5 • Phosphorus is a third period element 1 P atom x 5 valence electrons = 5 e- 5 F atoms x 7 valence electrons = 35 e- 40 e- total • Distributing the electrons results in this Lewis structure
  66. 66. Structures of Molecules Lewis Structures and Molecular Geometry: VSEPR Theory 3.4 Drawing Lewis • Molecular shape plays a large part in determining properties and shape • VSEPR theory - Valance Shell Electron Pair Repulsion theory • Used to predict the shape of the molecules • All electrons around the central atom arrange themselves so they can be as far away from each other as possible – to minimize electronic repulsion
  67. 67. Structures of Molecules VSEPR Theory 3.4 Drawing Lewis • In the covalent bond, bonding electrons are localized around the nucleus • The covalent bond is directional, having a specific orientation in space between the bonded atoms • Ionic bonds have electrostatic forces which have no specific orientation in space
  68. 68. Structures of Molecules Molecular Bonding 3.4 Drawing Lewis • Bonding pair = two electrons shared by 2 atoms – H:O • Nonbonding pair = two electrons belonging to 1 atom, pair not shared – N: • Maximal separation of bonding pairs = 4 corners of a TETRAHEDRON
  69. 69. 3.4 Molecular Geometry A Stable Exception to the Octet Rule • Consider BeH2 – Only 4 electrons surround the beryllium atom – These 2 electron pairs have minimal repulsion when located on opposite sides of the structure – Linear structure having bond angles of 180°
  70. 70. 3.4 Molecular Geometry Another Stable Exception to the Octet Rule • Consider BF3 – There are 3 shared electron pairs around the central atom – These electron pairs have minimal repulsion when placed in a plane, forming a triangle – Trigonal planar structure with bond angles of 120°
  71. 71. 3.4 Molecular Geometry Basic Electron Pair Repulsion of a Full Octet • Consider CH4 – There are 4 shared electron pairs around the central Carbon – Minimal electron repulsion when electrons are placed at the four corners of a tetrahedron – Each H-C-H bond angle is 109.5° • Tetrahedron is the primary structure of a full octet
  72. 72. 3.4 Molecular Geometry Basic Electron Pair Repulsion of a Full Octet with One Lone Pair Consider NH3 • There are 4 electron pairs around the central Nitrogen • 3 pairs are shared electron pairs • 1 pair is a lone pair – A lone pair is more electronegative with a greater electron repulsion – The lone pair takes one of the corners of the tetrahedron without being visible, distorting the arrangement of electron pairs • Ammonia has a trigonal pyramidal structure with 107° angles
  73. 73. 3.4 Molecular Geometry Basic Electron Pair Repulsion of a Full Octet with Two Lone Pairs Consider H2O • There are 4 electron pairs around the central Oxygen • 2 pairs are shared electron pairs • 2 pairs are lone pairs – All 4 electron pairs are approximately tetrahedral to each other – The lone pairs take two of the corners of the tetrahedron without being visible, distorting the arrangement of electron pairs • Water has a bent or angular structure with 104.5° bond angles
  74. 74. Predicting Geometric Shape UsingStructures of Molecules Electron Pairs 3.4 Drawing Lewis
  75. 75. Basic Procedure to DetermineStructures of Molecules Molecular Shape 3.4 Drawing Lewis 1. Write the Lewis structure 2. Count the number of shared electron pairs and lone pairs around the central atom 3. If no lone pairs are present, shape is: • 2 shared pairs - linear • 3 shared pairs - trigonal planar • 4 shared pairs - tetrahedral 1. Look at the arrangement and name the shape • Linear • Trigonal planar • Bent • Trigonal pyramid • Tetrahedral
  76. 76. Determine the MolecularStructures of Molecules Geometry 3.4 Drawing Lewis • PCl3 • SO2 • PH3 • SiH4
  77. 77. Lewis Structures and PolarityStructures of Molecules • A molecule is polar if its centers of positive and 3.4 Drawing Lewis negative charges do not coincide • Polar molecules when placed in an electric field will align themselves in the field • Molecules that are polar behave as a dipole (having two “poles” or ends) • One end is positively charged the other is negatively charged • Nonpolar molecules will not align themselves in an electric field
  78. 78. Structures of Molecules Determining Polarity To determine if a molecule is polar: 3.4 Drawing Lewis • Write the Lewis structure • Draw the geometry • Use the following symbol to denote the polarity of each bond Positive end of the Negative end of the bond, bond, the less more electronegative atom electronegative atom attracts the electrons more strongly towards it
  79. 79. Practice Determining PolarityStructures of Molecules Determine whether the following bonds and 3.4 Drawing Lewis molecules are polar: 1. Si – Cl 1. O2 2. H–C 2. HF 3. C–C 3. CH4 4. S – Cl 4. H2O
  80. 80. 3.5 Properties Based on ElectronicStructure and Molecular Geometry• Intramolecular forces – attractive forces within molecules – Chemical bonds• Intermolecular forces – attractive forces between molecules• Intermolecular forces determine many physical properties – Intermolecular forces are a direct consequence of the intramolecular forces in the molecules
  81. 81. Solubility and IntermolecularStructure and Molecular Geometry3.5 Properties Based on Electronic Forces Solubility - the maximum amount of solute that dissolves in a given amount of solvent at a specific temperature • “Like dissolves like” – Polar molecules are most soluble in polar solvents – Nonpolar molecules are most soluble in nonpolar solvents • Does ammonia, NH3, dissolve in water? • Yes, both molecules are polar
  82. 82. Interaction of Water andStructure and Molecular Geometry3.5 Properties Based on Electronic Ammonia • The δ- end of ammonia, N, is attracted to the δ+ end of the water molecule, H • The δ+ end of ammonia, H, is attracted to the δ- end of the water molecule, O • The attractive forces, called hydrogen bonds, pull ammonia into water, distributing the ammonia molecules throughout the water, forming a homogeneous solution
  83. 83. Structure and Molecular Geometry3.5 Properties Based on Electronic Interaction of Water and Oil • What do you know about oil and water? – “They don’t mix” • Why? – Because water is polar and oil is nonpolar • Water molecules exert their attractive forces on other water molecules • Oil remains insoluble and floats on the surface of the water as it is less dense
  84. 84. Boiling Points of LiquidsStructure and Molecular Geometry3.5 Properties Based on Electronic and Melting Points of Solids • Energy is used to overcome the intermolecular attractive forces in a substance, driving the molecules into a less associated phase • The greater the intermolecular force, the more energy is required leading to – Higher melting point of a solid – Higher boiling point of a liquid
  85. 85. Factors Influencing Boiling andStructure and Molecular Geometry3.5 Properties Based on Electronic Melting Points • Strength of the attractive force holding the substance in its current physical state • Molecular mass • Larger molecules have higher m.p. and b.p. than smaller molecules as it is more difficult to convert a larger mass to another phase • Polarity • Polar molecules have higher m.p. and b.p. than nonpolar molecules of similar molecular mass due to their stronger attractive force
  86. 86. 3.5 Properties Based on ElectronicStructure and Molecular Geometry Melting and Boiling Points – Selected Compounds by Bonding Type
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