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Objectives #1-2: Introduction to Chemical Bonding

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

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Objectives #1-2: Introduction to Chemical Bonding

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  1. 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 transferredin such a way so that each atom involved achieves the electron configuration of a noble gas!

  2. Formation of H-H Bond Lowers Energy

  3. Formation of the Noble Gas Configuration Through Bonding

  4. Objectives #1-2: Introduction to Chemical Bonding • Types of Chemical Bonds A. Ionic Bond • Involves the transferof valence electrons from a metalto a nonmetal • Formula units are formed, NOT molecules! • Pure Covalent aka NonpolarCovalent Bond • Involves the equal sharing of valence electrons between nonmetallic atoms • Molecules are formed • Polar Covalent Bond—Polar Bears!!  • Involves the unequal sharing of valence electrons between nonmetallic atoms • Polar molecules generally are formed, but there are exceptions! • Example diagrams:

  5. Formation of Ionic Bond Explain the differences in the ion size, based on trends... Note also that each ion charge is a result of transferring electrons! The formula unit is the lowest ratio of positive & negative charges needed to form the bond.

  6. Formation of Nonpolar Bond Note that only the SHARED electrons will form a new molecular orbital. Since atoms are of equal size, the shared elec. will spend equal time around each nucleus.

  7. Formation of Polar Bond Note that electrons are not distributed equally in this molecule, (as shown by the d-) so there will be areas that always have more of a negative charge than the central atom of sulfur. If the dipole is strong enough, it can influence the electron distribution of neighbouring molecules.

  8. 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: 0.0 - 0.3 Nonpolar (low ionic character) 0.3 – 1.7 Polar Covalent 1.7 – 4.0 Ionic (high ionic character) • Examples: H and H N and H F and F Ca and O

  9. Table of Electronegativities

  10. 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 decreasesthe 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 strongerthe bond will be; this same energy is also needed to breakthe bond • As the bond length between two atoms increases the bond energy decreases

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

  12. Bond Length vs. Bond Energy **Note that the bond length is a function of the number of electrons being shared between the atoms! Double and triple bonds have a shorter bond length & require more energy to break.

  13. Objectives #3-4: Lewis Structures and Covalent Bonding • Drawing Lewis Structures • General formula : • Examples • Single Covalent Bonds • Single covalent bonds involve the sharing of 1 pair of electrons • Steps to drawing Lewis structures for molecules: 1. Add up the # of valence electrons

  14. 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

  15. Single Bond Examples:

  16. Objectives #3-4: Lewis Structures and Covalent Bonding • Representations for Covalent Substances: Molecular Formula: Complete Structural Formula: Condensed Structural Formula: • Formation of Double Bonds • Double covalent bonds involve the sharing of 2pairs of electrons • Examples

  17. Objectives #3-4: Lewis Structures and Covalent Bonding • Formation of Triple Bonds • Triple covalent bonds involve the sharing of 3 pairs of electrons • Examples:

  18. 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:

  24. Example of Ionic Crystal

  25. Example of Covalent Network Crystal

  26. Example of Metallic Crystal

  27. Covalent Molecular Crystal

  28. 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

  29. 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

  30. 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:

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

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