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Lecture 15

sbc 200 Lecture Notes - Lecture 15: Ionic Bonding, Metallic Bonding, Formal ChargePremium

3 pages26 viewsFall 2016

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sbc 200

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Ionic bonding
involves the transfer of electrons and is usually observed when a metal bonds to a
Covalent bonding
involves the sharing of electrons and is usually observed when a nonmetal bonds to a
Metallic bonding
involves electron pooling and occurs when a metal bonds to another metal
Electronegativity and Oxidation Number
The more electronegative atom is assigned all the shared electrons.
The less electronegative atom is assigned none of the shared electrons.
Each atom in a bond is assigned all of its unshared electrons.
O.N. = # of valence e- (# of shared e- + # of unshared e- ) Electronegativities can be
used to assign oxidation numbers
The Ionic Bonding Model
An ionic bond is formed when a metal transfers electrons to a nonmetal to form ions,
which attract each other to give a solid compound
The total number of electrons lost by the metal atom(s) equals the total number of
electrons gained by the nonmetal atoms.
Bonding Pairs and Lone Pairs
Atoms share electrons to achieve a full outer level of electrons. The shared electrons are
called a shared pair or bonding pair.
An outer-level electron pair that is not involved in bonding is called a lone pair, or
unshared pair.
Electron Delocalization
Lewis structures depict electrons as localized either on an individual atom (lone pairs) or
in a bond between two atoms (shared pair). In a resonance hybrid, electrons are
delocalized: their density is “spread” over a few adjacent atoms.
Formal Charge
Formal charge is the charge an atom would have if all electrons were shared equally.
Formal charge of atom = # of valence e- - (# of unshared valence e- + ½ # of shared
valence e- )
Formal charges must sum to the actual charge on the species for all resonance forms
Resonance forms
Resonance forms with smaller formal charges are preferred. Resonance form I is
therefore not an important contributor
A negative formal charge should be placed on a more electronegative atoms, so
resonance form III is preferred to resonance form II.
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