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Lecture 3

CHMA10H3 Lecture Notes - Lecture 3: Electronegativity, Valence Electron, Covalent Bond

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Xiao- An Zhang

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Chapter 10
Modeling Bonding in Molecules
Covalent Bonding in Molecules
oThe bond is the net interaction composed of the nucleus - electron attractions, and
nucleus –nucleus repulsions and electro – electron repulsions
oOnly valence electrons of one atom participate in bonding with other atoms
A pure covalent bond = electron bonds are equally shared
An ionic bond = the most electronegative atom is where the pair of electrons are.
Polar covalent bonds are in between: the more the electron pair is shared equally the
more polar.
Lewis Structures
Show the distribution of valence e-
Covalent bonds are shown as dots
Does not show the shape of the molecules
Same number of valence electrons, same number of atoms and connectivity but
differ in the actual elements involved
Exceptions to the Octet Rule
oFor molecules that have less than 8 valence electrons
oOccurs for elements in third and higher periods
oOdd numbers of valence electrons
Free Radical Chemistry
When cooled Nitogen dioxide forms dintrogen tetraoxide
By forming a N-N bond
Theory of Resonance
This occurs when molecules can be represent in more than one way
The most accurate form is the intermediate between the them
Bond Order
The strength of bonding between two atoms
oDependent on the number of electrons
oType of orbital
o0.5 x (number of delocalized electrons/number of electrons in a bond)
Formal Charge
Determines which resonance structure is closest to the resonance hybrids
oFormal Charge = (valence e-) –(e in lone pair)- 0.5(bonded e-)
oThe sum of charges for the molecules must equal 0
oFor an ion it must be equal to the charge of the ion
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