Chemical Bonding

1. Chemical Bonding H Chemistry I Unit 4

2. Objectives #1-2 Introduction to Chemical Bonding • The Bonding Process *chemical bonds form so as to lower the energy of each atom involved in the bond *usually only involves the valence electrons in atoms *during the bonding process electrons are shared or transferred in such a way so that each atom involved achieve the electron configuration of a noble gas

3. Formation of H-H Bond Lowers Energy

4. Formation of the Noble Gas Configuration

5. Objectives #1-2 Introduction to Chemical Bonding • Types of Chemical Bonds • Ionic Bond *involves the transfer of valence electrons from a metal to a nonmetal *formula units are formed • Pure Covalent or Nonpolar Bond *involves the equalsharing of valence electrons between nonmetallic atoms *molecules are formed • Polar Covalent Bond *involves the unequal sharing of valence electrons between nonmetallic atoms *polar molecules result (but not always) *example diagrams:

6. Formation of Ionic Bond

7. Formation of Nonpolar Bond

8. Formation of Polar Bond

9. Objectives #1-2 Introduction to Chemical Bonding • Determining Expected Bond Type Through Electronegativity *differences in the electronegativity values of the atoms that bond together determine the type of bond that forms between them *the following scale is used to determine expected bond type: 0 - .3 Nonpolar (low ionic character) .3 – 1.7 Polar Covalent Beyond 1.7 Ionic (high ionic character) *examples:

10. Table of Electronegativities

11. Objectives #3-4 Lewis Structures and Covalent Bonding • Energy and Bonding *once the repulsive forces between atoms are overcome, a stable bond between nonmetals can form *bond formation decreases the overall energy of the atoms involved in the bond *the strength of a covalent bond can be expressed in its bond energy; the greater the bond energy the stronger the bond will be; this same energy is also needed to break the bond *as the bond length between two atoms increases the bond energy decreases

12. Effects of Repulsive Forces on the Formation of a Chemical Bond

13. Bond Length vs. Bond Energy

14. Objectives #3-4 Lewis Structures and Covalent Bonding • Drawing Lewis Structures *general formula and examples • Single Covalent Bonds *single covalent bonds involve the sharing of 1 pair of electrons *steps to drawing Lewis structures for molecules: 1. Sum valence electrons

15. Objectives #3-4 Lewis Structures and Covalent Bonding 2. Place lone atom in the center 3. Use single bonds to form bonds; complete octets or duets as needed with lone pairs 4. If valence count is exceeded, reduce number of lone pairs and use multiple bonds *lone pairs vs. bonding pairs: lone pairs occupy regions of molecule where bonds are not present in order to complete octets; help determine shape

16. Objectives #3-4 Lewis Structures and Covalent Bonding *examples of Lewis structures: *representations for covalent substances: (examples) • Formation of Double Bonds *double covalent bonds involve the sharing of 2 pairs of electrons *examples • Formation of Triple Bonds *triple covalent bonds involve the sharing of 3 pairs of electrons *examples:

17. Objectives #3-4 Lewis Structures and Covalent Bonding • Other Types of Organic Functional Groups *the functional group is the chemically active site on a carbon containing organic molecule

19. Objectives #5-7 Formation of Ions / Formation of Ionic Bonds / Properties of Ionic vs. Covalent Substances • Applications of the Octet Rule in Ionic Bonding • Formation of Cations *metals achieve octets by losing electrons • Formation of Anions *nonmetals achieve octets by gaining electrons *examples of cation and anion formation:

20. Objectives #5-7 Formation of Ions / Formation of Ionic Bonds / Properties of Ionic vs. Covalent Substances • Formation of Ionic Bond *the product of ionic bonding is the formation of a formula unit which shows the chemical formula of the compound in its lowest terms *the arrangement of ions in an ionic crystal is called the crystal lattice

21. Objectives #5-7 Formation of Ions / Formation of Ionic Bonds / Properties of Ionic vs. Covalent Substances *energy changes needed to form crystal lattice: (NaCl) • Formation of cation Na › Na+1 + e- addition of I.E., endothermic • Formation of anion Cl + e- › Cl-1 removal of E.A., exothermic • Formation of crystal lattice NaCl removal of lattice energy, exothermic

22. III. Characteristics of Ionic and Covalent Substances

23. IV. Crystalline Solids *solids usually exist as two types; amorphous solids which lack a definite crystalline structure such as wax or glass and crystalline solids which contain a definite crystalline structure called a crystal lattice such as in sodium chloride *the four major types of crystal structures and their properties are as follows:

25. Example of Ionic Crystal

26. Example of Covalent Network Crystal

27. Example of Metallic Crystal

28. Covalent Molecular Crystal

29. Objectives #8-9 VSEPR Theory and Molecular Polarity *steric number is the sum of the number of atoms attached to the central atom plus the number of lone pairs attached to the central atom *examples: *relationship of number of lone pairs and resulting bond angles: as the number of lone pairs on the central atom increases the bond angle decreases

30. Objective #10 Intermolecular Forces *intermolecular forces vs. intramolecular forces: attractive forces that operate between molecules • London Dispersion Forces *involves interactions between nonpolarmolecules • Dipole-dipole Interaction Forces *involves interactions between polar molecules

31. Objective #10 Intermolecular Forces • Hydrogen Bonding Forces *involve interactions between polar molecules and the element hydrogen; usually only involves polar molecules containing the elements F, O, and N *diagrams and examples of intermolecular forces:

32. Objective #10 Intermolecular Forces • Influence of Intermolecular Forces on Boiling and Melting Points (examples)