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Chapter 8 Basic Concepts of Chemical Bonding. 6.3 Describing Chemical Bonding Page: 288 - 330.

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Presentation on theme: "Chapter 8 Basic Concepts of Chemical Bonding. 6.3 Describing Chemical Bonding Page: 288 - 330."— Presentation transcript:

1 Chapter 8 Basic Concepts of Chemical Bonding

2 6.3 Describing Chemical Bonding Page:

3 Thermochemistry CHEMICAL BONDS IONIC Electrostatic attraction between ions. METALLIC Metal atoms bonded to several other atoms. COVALENT Sharing of electrons.

4 Thermochemistry The Ionic Bonding

5 Thermochemistry 8.2 The Ionic Bonding

6 Thermochemistry Na : loss of an electron Cl : gain of an electron The Ionic Bonding

7 Thermochemistry The Ionic Bonding 1. Ionization energy 2. Electron Affinity 3. Lattice Energy 4. Electronegativity Difference

8 Thermochemistry Na : loss of an electron Cl : gain of an electron One species must have very low ionization energy ( Na ) The Ionic Bonding

9 Thermochemistry Na : loss of an electron Cl : gain of an electron One species must have very high electron affinity ( Cl ) The Ionic Bonding

10 Thermochemistry The Ionic Bonding

11 Thermochemistry Attraction between oppositely charged ions  release of energy  formation of lattice LE is a measure of a stability of ions arranged within an ionic solid

12 Thermochemistry If the difference in electronegativity (ΔEN) between the species is: ΔEN > 1.7 An Ionic Bond would form between these species

13 Thermochemistry The Ionic Bonding SUMMARY

14 Thermochemistry

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17 6.3 THE COVALENT BONDING

18 Covalent Bonding

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20 Thermochemistry ELECTRONEGATIVITY in a molecule  is the ability of atoms in a molecule to attract electrons to themselves.

21 Thermochemistry DIPOLE and ELECTRONEGATIVITY  DIPOLE  DIPOLE: a partial separation of charge  One end of the molecule has slightly positive charge  The other end of the molecule has slightly negative charge

22 Slight excess of negative a negative charge Slight excess of positive a positive charge DIPOLE and ELECTRONEGATIVITY Slight excess of positive a positive charge

23 Thermochemistry DIPOLES are caused by ELECTRONEGATIVITY Chlorine has higher electronegativity The electrons spend MORE time around Chlorine Hydrogen has lower electronegativity The electrons spend LESS time around Hydrogen

24 BOND POLARITY In different compounds, electrons are not shared equally Homo nuclear diatomic compounds: H 2, Cl 2, O 2,N 2 … share electrons equally = NON POLAR COVALENT BOND

25 BOND POLARITY Hetero nuclear diatomic compounds: Hetero nuclear diatomic compounds: HF, HCl, NO, NaCl, LiO… DO NOT share electrons equally a. POLAR COVALENT BOND (the attraction of one of the atoms for the bonding electrons is LARGE )

26 BOND POLARITY Hetero nuclear diatomic compounds: Hetero nuclear diatomic compounds: HF, HCl, NO, NaCl, LiO… DO NOT share electrons equally a. POLAR COVALENT BOND (the attraction of one of the atoms for the bonding electrons is LARGE )

27 BOND POLARITY Hetero nuclear diatomic compounds: Hetero nuclear diatomic compounds: HF, HCl, NO, NaCl, LiO… DO NOT share electrons equally b. MOSTLY COVALENT BOND (the attraction of one of the atoms for the bonding electrons is SLIGHTLY GREATER )

28 Periodic Properties of the Elements © 2012 Pearson Education, Inc. BOND POLARITY Hetero nuclear diatomic compounds: Hetero nuclear diatomic compounds: HF, HCl, NO, NaCl, LiO… DO NOT share electrons equally a. POLAR COVALENT BOND (the attraction of one of the atoms for the bonding electrons is LARGE ) b. IONIC BONDS (the attraction of one of the atoms for the bonding electrons is VERY LARGE )

29 ELECTRONEGATIVITY greater the difference in electronegativity The greater the difference in electronegativity, the more polar the bond is

30 NON POLAR COVALENT BOND ELECTRONEGATIVITY MOSTLY COVALENT BOND POLAR COVALENT BOND IONIC BOND ΔE = 0 0 < ΔE < < ΔE < 1.7 ΔE > 1.7 H 2, Cl 2, O 2,N 2 MgO, NaCl, LiF H 2 O, CO 2, HF

31 NON POLAR COVALENT BOND H 2, Cl 2, O 2,N 2 POLAR COVALENT BOND H 2 O, CO 2, HF IONIC BOND MgO, NaCl, LiF ELECTRONEGATIVITY

32 Thermochemistry EXAMPLE In each case, which bond is more polar: a) B – Cl or C – Cl, b) P – F or P – Cl? Indicate in each case which atom has the partial negative charge.

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35 IONIC vs COVALENT Compounds Metal + nonmetal High melting point Lattice(crystal) structures Strong electrolytes Nonmetal + nonmetal Low melting point Low boiling point Non - electrolytes IONIC Bonding COVALENT Bonding

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37 HOMEWORK PAGE: PROBLEMS: all even 37

38 6.4 LEWIS STRUCTURE DIAGRAMS

39 LEWIS DIAGRAMS - REVIEW Show only an atom’s valence electrons and the chemical symbol.

40 LEWIS DIAGRAMS

41 Rule # 1 Dots representing valence electrons are placed around the element symbols

42 singly paired Electron dots are placed singly until the fifth electron is reached then they are paired Rule # 2

43 Lewis Diagrams of IONS and IONIC BONDS For positive ions, one electron dot is removed from the valence shell for each positive charge. For negative ions, one electron dot is added to each valence shell for each negative charge. Square brackets are placed around each ion to indicate transfer of electrons.

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45 LEWIS STRUCTURE DIAGRAMS for MOLECULES Lewis structures are representations of molecules showing all valence electrons: bonding and nonbonding

46 LEWIS STRUCTURE DIAGRAMS for MOLECULES Lewis structures are representations of molecules showing all valence electrons: bonding and nonbonding

47 Lewis Structures and Multiple Bonds two electron pairs When two electron pairs are shared, two lines are drawn, i.e. double bond ::O :: C :: O:: or ::O = C = O::

48 three electron pairs When three electron pairs are shared, three lines are drawn, i.e. triple bond :N ::: N: or :N ≡ N: Lewis Structures and Multiple Bonds

49 BOND LENGTHS The length of the bond between two atoms decreases as the number of shared electrons increases N ≡ N N = N N – N BOND STRENGTH?

50 STEPS TO FOLLOW… all atoms 1.Find the sum of valence electrons of all atoms in the polyatomic ion or molecule add a.If it is anion  add e- subtract b.If it is cation  subtract e- PCl 3

51 2. Write the symbols for the atoms –Make one of the atoms a central atom (usually the least electronegative atom) –connect it with the other atoms by single bonds STEPS TO FOLLOW… PCl 3

52 STEPS TO FOLLOW… 2. Write the symbols for the atoms –Subtract those electrons from your total number of valence electrons

53 3. Fill the octets of the outer atoms STEPS TO FOLLOW…

54 3. Fill the octets of the outer atoms STEPS TO FOLLOW…

55 Subtract the added electrons from your total number of valence electrons STEPS TO FOLLOW…

56 Subtract the added electrons from your total number of valence electrons STEPS TO FOLLOW…

57 4. Fill the octet of the central atom STEPS TO FOLLOW…

58 4. Fill the octet of the central atom STEPS TO FOLLOW…

59 5. If you run out of electrons before the central atom has an octet… …form multiple bonds until it does STEPS TO FOLLOW…

60 WORKSHEET EXAMPLE Draw Lewis Structures for a)CH 2 Cl 2 b)C 2 H 4 c)BrO 3 -

61 WORKSHEET EXAMPLE Draw Lewis Structures for a)NO b)BF 3 c)PF 5

62 EXCEPTIONTS TO THE OCTET RULE 1. For molecules and polyatomic ions containing an odd number of valence electrons 2. For molecules and polyatomic ions in which an atom has fewer than an octet of valence electrons

63 EXCEPTIONTS TO THE OCTET RULE 3. For molecules and polyatomic ions in which an atom has more than an octet of valence electrons

64 1. For molecules and polyatomic ions containing an odd number of valence electrons Complete pairing of valence electrons is impossible due to the odd number of valence electrons E.g.: ClO 2, NO, NO 2, O 2 -

65 2. For molecules and polyatomic ions in which an atom has fewer than an octet of valence electrons Not very common Mostly Boron or Beryllium compounds

66 3. For molecules and polyatomic ions in which an atom has more than an octet of valence electrons Very common Such molecules/ions are called HYPERVALENT Only for atoms of 3 rd period or higher 1. They have available and unfilled d orbitals for bonding 2. Their central atom (P, S, I, Xe…) is large enough to be bonded to even five different atoms (Cl, F or O)

67 Thermochemistry EXAMPLE Draw a Lewis Structure for ion: ICl 4 -

68 Thermochemistry EXAMPLE Draw a Lewis Structure for the thiocyanate ion: NCS -

69 Thermochemistry

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71 FORMAL CHARGE the atom electronegativity The charge the atom would have if all the atoms in the molecule had the same electronegativity

72 FORMAL CHARGE OF AN ATOM = # of VALENCE ELECTRON – # OF ELECTRONS ASSIGNED

73 Thermochemistry EXAMPLE What are the formal charges of C and N in the cyanide ion: CN - ? [:C ≡ N:] - # of VALENCE ELECTRON – # OF ELECTRONS ASSIGNED

74 Thermochemistry EXAMPLE What are the formal charges of C and N in the cyanide ion: CN - ? [:C ≡ N:] - # of VALENCE ELECTRON – # OF ELECTRONS ASSIGNED CN Valence e-45 Assigned e-55 Formal Charge0 0

75 Thermochemistry WORKSHEET EXAMPLE What are the formal charges on the thiocyanate ions? WHICH STRUCTURE IS THE MOST IMPORTANT (DOMINANT) ONE?

76 Thermochemistry WORKSHEET EXAMPLE What are the formal charges the thiocyanate ions? WHICH STRUCTURE IS THE MOST IMPORTANT (DOMINANT) ONE?

77 Thermochemistry WORKSHEET EXAMPLE The cyanate ion, NCO-, has three possible Lewis structures. a)Draw these three structures assign formal charges in each. b)Which Lewis structure is dominant?

78 8.6 RESONANCE STRUCTURES Draw a Lewis Structure of OZONE, O 3

79 RESONANCE STRUCTURES OZONE : A mix of different resonance structures GREEN PAINT : A mix of different colors

80 RESONANCE STRUCTURES Somewhere between single bond and double bond

81 RESONANCE STRUCTURES Is the use of two or more Lewis structures to represent a molecule this is because that molecule can not be represented by only a single Lewis structure

82 Basic Concepts of Chemical Bonding © 2012 Pearson Education, Inc. In truth, the electrons that form the second C—O bond in the double bonds below do not always sit between that C and that O, but rather can move among the two oxygen atoms and the carbon. They are not localized ; they are delocalized. RESONANCE STRUCTURES

83 Basic Concepts of Chemical Bonding © 2012 Pearson Education, Inc. RESONANCE STRUCTURES The organic compound benzene, C 6 H 6, has two resonance structures. It is a hexagon with a circle inside to signify the delocalized electrons in the ring.

84 Thermochemistry EXAMPLE What are the resonance structures of nitrate ion: NO 3 -

85 Thermochemistry WORKSHEET EXAMPLE Using Formal Charges and the concept of Resonance, show why the correct Lewis structure of BF 3 is the one in which B has an incomplete octet and only single bonds are present.

86 8.8 STRENGTHS OF COVALENT BONDS Learn on your own

87 HOMEWORK PAGE: PROBLEMS: 49, 51, 53, 55, 57, 61, 67, 69, 71, 73, 87

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89 Thermochemistry WORKSHEET EXAMPLE Copy this table and fill out the missing information.

90 Thermochemistry WORKSHEET EXAMPLE Which substance would you expect to have the greatest lattice energy, MgF 2, CaF 2, and ZrO 2 ? ZrO 2

91 Thermochemistry WORKSHEET EXAMPLE Ionizing an H 2 molecule to H 2 + changes the strength of the bond. Based on the description of covalent bonding given previously, do you expect the bond H—H in H 2 + to be weaker or stronger than the bond in H 2 ? Weaker. In both H 2 and H 2 + the two H atoms are principally held together by the electrostatic attractions between the nuclei and the electron(s) concentrated between them. H 2 + has only one electron between the nuclei whereas H 2 has two and this results in the H—H bond in being stronger.

92 Thermochemistry WORKSHEET EXAMPLE How does the ELECTRONEGATIVITY of an element differ from its ELECTRON AFFINITY? Electron affinity measures: a.the energy released when an isolated atom gains an electron to form a 1- ion. The electronegativity measures: a.the ability of the atom to hold on to its own electrons b.the ability of the atom to attract electrons from other atoms in compounds.

93 Thermochemistry WORKSHEET EXAMPLE In each case, which bond is more polar: a) B – Cl or C – Cl, b) P – F or ? Indicate in each case which atom has the partial negative charge.

94 Thermochemistry WORKSHEET EXAMPLE The cyanate ion, NCO-, has three possible Lewis structures. a)Draw these three structures assign formal charges in each. b)Which lewis structure is dominant?

95 Thermochemistry WORKSHEET EXAMPLE Using Formal Charges and the concept of Resonance, show why the correct Lewis structure of BF 3 is the one in which B has an incomplete octet and there are only single bonds present. –Giving boron a filled octet places a negative charge on the boron and a positive charge on fluorine. –This would not be an accurate picture of the distribution of electrons in BF 3. –Therefore, structures that put a double bond between boron and fluorine are much less important than the one that leaves boron with only 6 valence electrons.


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