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Introductory Chemistry , 3 rd Edition Nivaldo Tro

Introductory Chemistry , 3 rd Edition Nivaldo Tro. Chapter 10 Chemical Bonding. Basic Principles of Chemistry Online Southeast Missouri State University Cape Girardeau, MO. 2009, Prentice Hall. Bonding Theories. Bonding is the way atoms attach to make molecules.

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Introductory Chemistry , 3 rd Edition Nivaldo Tro

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  1. Introductory Chemistry, 3rd EditionNivaldo Tro Chapter 10 Chemical Bonding Basic Principles of Chemistry Online Southeast Missouri State University Cape Girardeau, MO 2009, Prentice Hall

  2. Bonding Theories • Bonding is the way atoms attach to make molecules. • An understanding of how and why atoms attach together in the manner they do is central to chemistry. • Chemists have an understanding of bonding that allows them to: • Predict the shapes of molecules and properties of substances based on the bonding within the molecules. • Design and build molecules with particular sets of chemical and physical properties. Tro's Introductory Chemistry, Chapter 10

  3. Lewis Theory • Lewis bonding theory emphasizes the importance of valence electrons. • Uses dots to represent valence electrons either on or shared by atoms. • Arranges bonding between atoms to attain certain sets of stable valence electron arrangements. Tro's Introductory Chemistry, Chapter 10

  4. • •• •• •• •• Li• Be• •B• •C• •N• •O::F: :Ne: • • • • • • •• Lewis Symbols of Atoms • Also known as electron dot symbols. • Uses symbol of element to represent nucleus and inner electrons. • Uses dots around the symbol to represent valence electrons. • Puts one electron on each side first, then pair. • Remember that elements in the same group have the same number of valence electrons; therefore, their Lewis dot symbols will look alike. Tro's Introductory Chemistry, Chapter 10

  5. Practice—Write the Lewis Symbol for Arsenic. Tro's Introductory Chemistry, Chapter 10

  6. Practice—Write the Lewis Symbol for Arsenic, Continued. • As is in column 5A, therefore it has 5 valence electrons. Tro's Introductory Chemistry, Chapter 10

  7. Lewis Bonding Theory • Atoms bond because it results in a more stable electron configuration. • Atoms bond together by either transferring or sharing electrons. • Usually this results in all atoms obtaining an outer shell with 8 electrons. • Octet rule. • There are some exceptions to this rule—the key to remember is to try to get an electron configuration like a noble gas. • Li and Be try to achieve the He electron arrangement. Tro's Introductory Chemistry, Chapter 10

  8. •• •• Li• Li+:F: [:F:]− • •• Lewis Symbols of Ions • Cations have Lewis symbols without valence electrons. • Lost in the cation formation. • They now have a full “outer” shell that was the previous second highest energy shell. • Anions have Lewis symbols with 8 valence electrons. • Electrons gained in the formation of the anion. Tro's Introductory Chemistry, Chapter 10

  9. Practice—Show How the Electrons Are Transferred and the Bond Is Formed When Na Reacts with S. Tro's Introductory Chemistry, Chapter 10

  10. Practice—Show How the Electrons Are Transferred and the Bond Is Formed When Na Reacts with S, Continued. Tro's Introductory Chemistry, Chapter 10

  11. Ionic Bonds • Metal to nonmetal. • Metal loses electrons to form cation. • Nonmetal gains electrons to form anion. • Ionic bond results from + to − attraction. • Larger charge = stronger attraction. • Smaller ion = stronger attraction. • Lewis theory allows us to predict the correct formulas of ionic compounds. Tro's Introductory Chemistry, Chapter 10

  12. ∙ ∙ ∙ ∙ ∙ Ca Ca Cl Cl Cl ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ Example 10.3—Using Lewis Theory to Predict Chemical Formulas of Ionic Compounds Predict the formula of the compound that forms between calcium and chlorine. Draw the Lewis dot symbols of the elements. Transfer all the valance electrons from the metal to the nonmetal, adding more of each atom as you go, until all electrons are lost from the metal atoms and all nonmetal atoms have 8 electrons. Ca2+ CaCl2 Tro's Introductory Chemistry, Chapter 10

  13. Practice—Use Lewis Symbols to Predict the Formula of an Ionic Compound Made from Reacting a Metal, M, that Has 2 Valence Electrons with a Nonmetal, X, that Has 5 Valence Electrons. Tro's Introductory Chemistry, Chapter 10

  14. Practice—Use Lewis Symbols to Predict the Formula of an Ionic Compound Made from Reacting a Metal, M, that Has 2 Valence Electrons with a Nonmetal, X, that Has 5 Valence Electrons, Continued. M3X2 Tro's Introductory Chemistry, Chapter 10

  15. Covalent Bonds • Often found between two nonmetals. • Typical of molecular species. • Atoms bonded together to form molecules. • Strong attraction. • Atoms share pairs of electronsto attain octets. • Molecules generally weakly attracted to each other. • Observed physical properties of molecular substance due to these attractions. Tro's Introductory Chemistry, Chapter 10

  16. Using Lewis Atomic Structures to Predict Bonding Between Nonmetal Atoms • Nonmetal atoms often bond to achieve an octet of valence electrons by sharing electrons. • Though there are many exceptions to the Octet rule. • In Lewis theory, atoms share electrons to complete their octet. • This may involve sharing electrons with multiple atoms or sharing multiple pairs of electrons with the same atom. Tro's Introductory Chemistry, Chapter 10

  17. •• •• • • •• F F •• •• •• •• •• •• •• •• F F F F •• •• Single Covalent Bonds • Two atoms share one pair of electrons. • 2 electrons. • One atom may have more than one single bond. •• • • • • H H O •• •• •• H H •• O •• Tro's Introductory Chemistry, Chapter 10

  18. •• •• • • • • O O •• •• •• •• O •• •• •• •• O O O Double Covalent Bond • Two atoms sharing two pairs of electrons. • 4 electrons. • Shorter and stronger than single bond. Tro's Introductory Chemistry, Chapter 10

  19. •• •• • • • • N N • • N N Triple Covalent Bond • Two atoms sharing 3 pairs of electrons. • 6 electrons. • Shorter and stronger than single or double bond. N N •• •• •• •• •• Tro's Introductory Chemistry, Chapter 10

  20. •• •• Bonding and Lone Pair Electrons • Electrons that are shared by atoms are called bonding pairs. • Electrons that are not shared by atoms but belong to a particular atom are called lone pairs. • Also known as nonbonding pairs. O S O •• •• Bonding pairs Lone pairs • • •• •• • • • • Tro's Introductory Chemistry, Chapter 10

  21. Multiplicity and Bond Properties • The more electrons two atoms share, the stronger they are bonded together. • This explains the observation that triple bonds are stronger than similar double bonds, which are stronger than single bonds. • C≡N is stronger than C=N, C=N is stronger than C─N. • This explains the observation that triple bonds are shorter than similar double bonds, which are shorter than single bonds. • C≡N is shorter than C=N, C=N is shorter than C─N Tro's Introductory Chemistry, Chapter 10

  22. Trends in Bond Length and Energy

  23. Polyatomic Ions • The polyatomic ions are attracted to opposite ions by ionic bonds. • Form crystal lattices. • Atoms in the polyatomic ion are held together by covalent bonds. Tro's Introductory Chemistry, Chapter 10

  24. Lewis Formulas of Molecules • Shows pattern of valence electron distribution in the molecule. • Useful for understanding the bonding in many compounds. • Allows us to predict shapes of molecules. • Allows us to predict properties of molecules and how they will interact together. Tro's Introductory Chemistry, Chapter 10

  25. C B N O F Lewis Structures • Some common bonding patterns. • C = 4 bonds & 0 lone pairs. • 4 bonds = 4 single, or 2 double, or single + triple, or 2 single + double. • N = 3 bonds & 1 lone pair. • O = 2 bonds & 2 lone pairs. • H and halogen = 1 bond. • Be = 2 bonds & 0 lone pairs. • B = 3 bonds & 0 lone pairs. Tro's Introductory Chemistry, Chapter 10

  26. Writing Lewis Structuresfor Covalent Molecules 1. Attach the atoms together in a skeletal structure. • Most metallic element is generally central. • In PCl3, the P is central because it is further left on the periodic table and therefore more metallic. • Halogens and hydrogen are generally terminal. • In C2Cl4, the Cs are attached together in the center and the Cls are surrounding them. • Many molecules tend to be symmetrical. • Though there are many exceptions to this, chemical formulas are often written to indicate the order of atom attachment. • In C2Cl4, there are two Cls on each C. • In oxyacids, the acid hydrogens are attached to an oxygen. • In H2SO4, the S is central, the Os are attached to the S, and each H is attached to a different O. Tro's Introductory Chemistry, Chapter 10

  27. Writing Lewis Structuresfor Covalent Molecules, Continued 2. Calculate the total number of valence electrons available for bonding. • Use group number of periodic table to find number of valence electrons for each atom. • If you have a cation, subtract 1 electron for each + charge. • If you have an anion, add 1 electron for each − charge. • In PCl3, P has 5 e− and each Cl has 7 e− for a total of 26 e−. • In ClO3−, Cl has 7 e− and each O has 6 e− for a total of 25 e−. • Add 1 e − for the negative charge to get a grand total of 26 e− Tro's Introductory Chemistry, Chapter 10

  28. Writing Lewis Structuresfor Covalent Molecules, Continued 3. Attach atoms with pairs of electrons and subtract electrons used from total. • Bonding electrons. 4. Add remaining electrons in pairs to complete the octets of all the atoms. • Remember H only wants 2 electrons. • Don’t forget to keep subtracting from the total. • Complete octets on the terminal atoms first, then work toward central atoms. Tro's Introductory Chemistry, Chapter 10

  29. Writing Lewis Structuresfor Covalent Molecules, Continued 5. If there are not enough electrons to complete the octet of the central atom, bring pairs of electrons from an attached atom in to share with the central atom until it has an octet. • Try to follow common bonding patterns. Tro's Introductory Chemistry, Chapter 10

  30. Example HNO3 1. Write skeletal structure. • Since this is an oxyacid, H on outside attached to one of the Os; N is central. 2. Count valence electrons. N = 5 H = 1 O3 = 3∙6 = 18 Total = 24 e- Tro's Introductory Chemistry, Chapter 10

  31. Example HNO3 , Continued 3. Attach atoms with pairs of electrons and subtract from the total. N = 5 H = 1 O3 = 3∙6 = 18 Total = 24 e- Electrons Start 24 Used 8 Left 16 Tro's Introductory Chemistry, Chapter 10 31

  32. Example HNO3 , Continued 4. Complete octets, outside-in. • H is already complete with 2. • 1 bond. • Keep going until all atoms have an octet or you run out of electrons. N = 5 H = 1 O3 = 3∙6 = 18 Total = 24 e- Electrons Start 24 Used 8 Left 16 Electrons Start 16 Used 16 Left 0 Tro's Introductory Chemistry, Chapter 10

  33. Example HNO3 , Continued 5. If central atom does not have octet, bring in electron pairs from outside atoms to share. • Follow common bonding patterns if possible. Tro's Introductory Chemistry, Chapter 10

  34. Example 10.4—Writing Lewis Structures forCovalent Compounds Tro's Introductory Chemistry, Chapter 10 34

  35. Example 10.4: Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapter 10

  36. Write down the given quantity and its units. Given: CO2 Example:Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapter 10

  37. Write down the quantity to find and/or its units. Find: Lewis structure Information: Given: CO2 Example:Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapter 10

  38. Design a solution map. Information: Given: CO2 Find: Lewis structure Example:Write the Lewis structure of CO2. Formula of compound Lewis structure Count and distribute electrons Skeletal structure Tro's Introductory Chemistry, Chapter 10

  39. Apply the solution map. Write skeletal structure. Least metallic atom central. H terminal. Symmetry. Information: Given: CO2 Find: Lewis structure Solution Map: formula → skeletal → electron distribution → Lewis Example:Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapter 10

  40. Apply the solution map. Count and distribute the valence electrons. Count valence electrons. Information: Given: CO2 Find: Lewis structure Solution Map: formula → skeletal → electron distribution → Lewis C = 4 O = 2 ∙ 6 Total CO2 = 16 Example:Write the Lewis structure of CO2. 1A 8A 3A 4A 5A 6A 7A 2A C O Tro's Introductory Chemistry, Chapter 10

  41. Apply the solution map. Count and distribute the valence electrons. Attach atoms. Information: Given: CO2 Find: Lewis structure Solution Map: formula → skeletal → electron distribution → Lewis C = 4 O = 2 ∙ 6 Total CO2 = 16 Start = 16 e- Used = 4 e- Left = 12 e- Example:Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapter 10

  42. Apply the solution map. Count and distribute the valence electrons. Complete octets. Outside atoms first. Information: Given: CO2 Find: Lewis structure Solution Map: formula → skeletal → electron distribution → Lewis C = 4 O = 2 ∙ 6 Total CO2 = 16 Start = 16 e- Used = 4 e- Left = 12 e- Start = 12 e- Used = 12 e- Left = 0 e- Example:Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapter 10

  43. Apply the solution map. Count and distribute the valence electrons. Complete octets. If not enough electrons to complete octet of central atom, bring in pairs of electrons from attached atom to make multiple bonds. Information: Given: CO2 Find: Lewis structure Solution Map: formula → skeletal → electron distribution → Lewis Start = 12 e- Used = 12 e- Left = 0 e- Example:Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapter 10

  44. Check: Information: Given: CO2 Find: Lewis structure Solution Map: formula → skeletal → electron distribution → Lewis Start C = 4 e- O = 2 ∙ 6 e- Total CO2 = 16 e- End Bonding = 4 ∙ 2 e- Lone pairs = 4 ∙ 2 e- Total CO2 = 16 e- Example:Write the Lewis structure of CO2. The skeletal structure is symmetrical. All the electrons are accounted for. Tro's Introductory Chemistry, Chapter 10

  45. Writing Lewis Structures forPolyatomic Ions • The procedure is the same, the only difference is in counting the valence electrons. • For polyatomic cations, take away one electron from the total for each positive charge. • For polyatomic anions, add one electron to the total for each negative charge. Tro's Introductory Chemistry, Chapter 10

  46. Example NO3─ 1. Write skeletal structure. • N is central because it is the most metallic. 2. Count valence electrons. N = 5 O3 = 3∙6 = 18 (-) = 1 Total = 24 e- Tro's Introductory Chemistry, Chapter 10

  47. Example NO3─ , Continued 3. Attach atoms with pairs of electrons and subtract from the total. Electrons Start 24 Used 6 Left 18 N = 5 O3 = 3∙6 = 18 (-) = 1 Total = 24 e- Tro's Introductory Chemistry, Chapter 10 47

  48. Example NO3─ , Continued 3. Complete octets, outside-in. • Keep going until all atoms have an octet or you run out of electrons. N = 5 O3 = 3∙6 = 18 (-) = 1 Total = 24 e- Electrons Start 24 Used 6 Left 18 Electrons Start 18 Used 18 Left 0 Tro's Introductory Chemistry, Chapter 10

  49. Example NO3─ , Continued 5. If central atom does not have octet, bring in electron pairs from outside atoms to share. • Follow common bonding patterns if possible. Tro's Introductory Chemistry, Chapter 10

  50. Practice—Lewis Structures NClO H3BO3 NO2-1 H3PO4 SO3-2 P2H4 Tro's Introductory Chemistry, Chapter 10 50

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