Chapter8LectureNotes

Chapter8LectureNotes - Chapter 8 Zumdahl AP Chem Lecture...

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Chapter 8 Zumdahl AP Chem Lecture Problems 15 17 25 27 31 35 41 43 51 57 59 61 63 71 73 77 79 81 83 85 CHEMICAL BONDING Lecture 1 Chemical Bonds form because the ENERGY of the system is LOWER than if the bonds do not form (In other words, bonds allow systems to have lower energy than in an unbonded state). Bond Length distance between two atoms where the energy is the LEAST Ionic Bond attraction due to electrostatic interaction (positive and negative charges) Page 346 has a good diagram 1. too close; nuclei repel 2. too far apart; ions attract (bond length is the “best” compromise between these two forces) Coulomb’s Law Energy of ionic bonds is DIRECTLY proportional to the product of the ion charges and INVERSELY proportional to the distance between the ions (very important concept) Covalent Bond explains the attraction between to adjacent atoms because of the electrons being shared approximately equally. If shared equally, (Examples ) “nonpolar bond” If shared unequally (Examples ) “polar covalent bond” So covalent bonds can be POLAR or NONPOLAR depending on each atom’s ability to attract electrons. This ability is called electronegativity . (page 348 has a table) The basic trend of electronegativity is that it DECREASES as you go DOWN or TO THE LEFT on the periodic table. We calculate a e.n. for the two atoms in a bond. If the difference is high, the bond is very polar and has a high “ionic nature.” If low, the bond has a high covalent nature.
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Ex Which bond is more polar? H—F Na—Cl C—H NaCl is so polar, electron TRANSFER can occur, but we realize that even here, there is some small “covalent nature” to the bond (there are no strict cutoffs as we simplistically say in high school chem classes) Molecular Polarity from Bond Polarity If we combine the distance, angle, and polarities of the different bonds in a molecule, we get a number called a “dipole moment.” (“moments” are another way of talking about forces in physics). The IMPORTANT thing to see is that individual polar bonds (dipoles) can either cancel or not cancel in the overall molecule, and therefore yield overall polar or nonpolar molecules Ex CH 4 CH 3 Cl Bonding and Electron Configurations
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Chapter8LectureNotes - Chapter 8 Zumdahl AP Chem Lecture...

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