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Chapter 10.1-10.4

CHEM 112 Chapter Notes - Chapter 10.1-10.4: Chemical Polarity, Coordinate Covalent Bond, Electric Potential


Department
Chemistry
Course Code
CHEM 112
Professor
Gang Wu
Chapter
10.1-10.4

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Chemistry Week 4
10-1
Lewis theory
1. Electrons, especially valence electrons, play a fundamental role in chemical bonding
2. In some cases, electrons are transferred from one atom to another; these are ionic bonds
3. In other cases, electrons are shared between atoms; these are covalent bonds
4. Electrons are transferred or shared in such a way that each atom acquires a stable electron configuration. Usually this is a noble gas
configuration with 8 outer shell electrons or an octet
Lewis symbols and Lewis structures
o A Lewis symbol consists of the chemical symbol to represent the nucleus and core electrons of an atom , together with dots places
around the symbol to represent the valence electrons
o A Lewis structure is a combination of Lewis symbols that represents either the transfer or sharing in a chemical bond
Lewis structures for ionic compounds
o No bond is 100% ionic
o Both the charges of the anion and the cation are shown
10-2
Covalent bonding
Octet rule - a requirement of 8 valence electrons
Single covalent bond - the sharing of a single pair of electrons between bonded atoms
Bond pair applies to a pair of electrons in a covalent bond
Lone pair applies to the pairs of electrons that are not involved in bonding
Coordinate covalent bond
o A covalent bond in which a single atom contributes both of the electrons to a shared pair
Multiple covalent bonds
o Double covalent bond bonded atoms share two pairs of
electrons between them
o Triple covalent bond bonded atoms share three pairs of
electrons between them
10-3
Polar covalent bonds and electrostatic potential maps
A covalent bond in which electrons are not shared equally between two atoms is a polar covalent bond
Electrons are displaced towards the more nonmetallic element
The more nonmetallic element is signified with a and the more metallic element is signified with a +
o Called potential charge
Electrostatic potential map a way to visualize the charge distribution
The electrostatic potential is the work done in moving a unit of positive charge at a constant speed from one molecule to another
o Obtained by hypothetically probing an electron density surface with a positive point charge
o When positive point charge is attracted to an electron rich region, electrostatic potential is negative
o When positive point charge is attracted to an electron weak region, electrostatic potential is positive
o For a neutral atom if the potential at a point is positive then it is likely that the molecule has a net positive charge
o Red is low energy and most negative electrostatic potential of the spectrum and blue is the most positive electrostatic
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