CHEM 141 Chapter Notes - Chapter 7-8: Debye, Electric Potential, Formal Charge

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6.2
Pure covalent -- e-s are shared equally
Polar covalent -- partially charged atoms are held together by unequal sharing of e-s
Electrostatic potential models -- show regions where e-s spend a lot of time in as red and regions where e-s don't spend a lot of time in as
blue
Electronegativity -- increases from left to right -- decreases as metallic character increases
-different from EA
EA - refers to an isolated atom's ability to attract additional e-s
Electronegativity - refers to an atom in a chemical bond
When it's between 0.5 and 2.0 -- polar covalent
When it's > 2.0 -- ionic
Dipole moment -- a quantitative measure of the polarity of a bond
When the charges have a discrete instead of a partial value -- ionic
Dipole moments are usually expressed In debye units (D)
Diatomic neutral molecules that are polar have the same magnitude of partial negative and positive charges -- the calculated dipole
moment would be positive
-if the charges on the atom are discrete rather than partial then it means that the e- has been completely transferred
Percent ionic character:
6.5
Resonance structures -- diagrams that show the different arrangements of e-s for a molecule
The structures themselves do not exist -- resonance structures together best explain properties
Eg.
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Eg.
However, not all resonance structures are equivalent:
Eg.
Relative stability of resonance structures:
-when all atoms have full octets
-smaller non-zero formal charges are preferred if possible
-same nonzero formal charge on adjacent atoms are NOT preferred
The structure that is most stable is NOT the true form -- the true form is very similar to the most stable resonance structure
Eg.
No ONE structure would be enough to describe the actual bonding
Coordinate covalent -- all e-s are provided by one atom
-However, properties of this bond won't differ from those of normal bonds
Lewis -base -- can donate an e- pair
-acid -- can accept an e- pair
Free radicals -- molecules with an odd # of e-s -- highly reactive
-atoms with d orbitals can form extended octets
7.1
VSEPR -- based on assumption that e-s will repulse each other so that e- domains will be as far away from each other as possible, thus
minimizing the repulsive interactions between them
e- domain geometry -- arrangement of e- domains
Molecular geometry -- arrangement of atoms
-when there's no lone pairs, e- domain geo. = molecular geo.
Without lone pairs:
AB2 -- linear -- 180
AB3 -- trigonal planar -- 120
AB4 -- tetrahedral -- 109.5
AB5 -- trigonal bipyramid -- 90 (equatorial) or 120 (axial)
AB6-- octahedral -- 90
Molecular geo differs e- domain geo when there are lone pairs:
Eg.
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Document Summary

Polar covalent -- partially charged atoms are held together by unequal sharing of e-s. Electrostatic potential models -- show regions where e-s spend a lot of time in as red and regions where e-s don"t spend a lot of time in as blue. Electronegativity -- increases from left to right -- decreases as metallic character increases. Ea - refers to an isolated atom"s ability to attract additional e-s. Electronegativity - refers to an atom in a chemical bond. When it"s between 0. 5 and 2. 0 -- polar covalent. Dipole moment -- a quantitative measure of the polarity of a bond. When the charges have a discrete instead of a partial value -- ionic. Dipole moments are usually expressed in debye units (d) Diatomic neutral molecules that are polar have the same magnitude of partial negative and positive charges -- the calculated dipole moment would be positive.

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