1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Bonds Forces that hold groups of atoms together and make them function as a unit.

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Bond Energy 4 It is the energy required to break a bond. 4 It gives us information about the strength of a bonding interaction.

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Bond Length The distance where the system energy is a minimum.

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Ionic Bonds 4 Formed from electrostatic attractions of closely packed, oppositely charged ions. 4 Formed when an atom that easily loses electrons reacts with one that has a high electron affinity.

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Electronegativity The ability of an atom in a molecule to attract shared electrons to itself.

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Polarity A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment.

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Achieving Noble Gas Electron Configurations (NGEC) Two nonmetals react: They share electrons to achieve NGEC. A nonmetal and a representative group metal react (ionic compound): The valence orbitals of the metal are emptied to achieve NGEC. The valence electron configuration of the nonmetal achieves NGEC.

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Isoelectronic Ions Ions containing the the same number of electrons (O 2 , F , Na +, Mg 2+, Al 3+ ) O 2  > F  > Na + > Mg 2+ > Al 3+ largest smallest

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Lattice Energy The change in energy when separated gaseous ions are packed together to form an ionic solid. M + (g) + X  (g)  MX(s) Lattice energy is negative (exothermic) from the point of view of the system.

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Formation of an Ionic Solid 1.Sublimation of the solid metal M(s)  M(g) [endothermic] 2.Ionization of the metal atoms M(g)  M + (g) + e  [endothermic] 3.Dissociation of the nonmetal 1 / 2 X 2 (g)  X(g) [endothermic]

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Formation of an Ionic Solid (continued) 4.Formation of X  ions in the gas phase: X(g) + e   X  (g) [exothermic] 5.Formation of the solid MX M + (g) + X  (g)  MX(s) [quite exothermic]

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Q 1, Q 2 = charges on the ions r = shortest distance between centers of the cations and anions

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Models Models are attempts to explain how nature operates on the microscopic level based on experiences in the macroscopic world.

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Fundamental Properties of Models 4 A model does not equal reality. 4 Models are oversimplifications, and are therefore often wrong. 4 Models become more complicated as they age. 4 We must understand the underlying assumptions in a model so that we don’t misuse it.

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Bond Energies Bond breaking requires energy (endothermic). Bond formation releases energy (exothermic).  H =  D( bonds broken )   D( bonds formed ) energy requiredenergy released

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Localized Electron Model A molecule is composed of atoms that share electron pair orbitals.

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Localized Electron Model 1.Description of valence electron arrangement (Lewis structure). 2.Prediction of geometry (VSEPR model). 3.Description of atomic orbital types used to share electrons or hold long pairs.

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Lewis Structure 4 Shows how valence electrons are arranged among atoms in a molecule. 4 Reflects central idea that stability of a compound relates to noble gas electron configuration.

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Drawing Lewis Dot Structures 1.Count the valence electrons. 2.Predict the location of the atoms 1.Hydrogen is a terminal atom 2.The central atom has the smallest electronegativity. 3.Draw a pair of electrons between the central atom and the surrounding atoms. 4.Use the remaining electrons to complete the octets of each atom. If there are electrons left over, place them on the central atom. 5.If the central atom does not have a complete octet then try double or triple bonds. 1. If the atom has 1, 2, or 3 valence electrons, it doesn’t require an octet.

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Comments About the Octet Rule 4 2nd row elements C, N, O, F observe the octet rule. 4 2nd row elements B and Be often have fewer than 8 electrons around themselves - they are very reactive. 4 3rd row and heavier elements CAN exceed the octet rule using empty valence d orbitals. 4 When writing Lewis structures, satisfy octets first, then place electrons around elements having available d orbitals.

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Resonance Occurs when more than one valid Lewis structure can be written for a particular molecule. These are resonance structures. The actual structure is an average of the resonance structures.

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 VSEPR Model The structure around a given atom is determined principally by minimizing electron pair repulsions.

23. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Predicting a VSEPR Structure 1.Draw Lewis structure. 2.Put pairs as far apart as possible. 3.Determine positions of atoms from the way electron pairs are shared. 4.Determine the name of molecular structure from positions of the atoms.

24. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Hybridization The mixing of atomic orbitals to form special orbitals for bonding. The atoms are responding as needed to give the minimum energy for the molecule.

25. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 A sigma (  ) bond centers along the internuclear axis. A pi (  ) bond occupies the space above and below the internuclear axis.

26. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Localized Electron Model 4 Draw the Lewis structure(s) 4 Determine the arrangement of electron pairs (VSEPR model). 4 Specify the necessary hybrid orbitals.

27. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Paramagnetism 4 unpaired electrons 4 attracted to induced magnetic field 4 much stronger than diamagnetism

28. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 Diamagnetism 4 paired electrons 4 repelled from induced magnetic field 4 much weaker than paramagnetism