Gen Concepts Chemical Bonding Sheet Page 2
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1
2
3The covalent bond between two atoms depends on the
balanc e of attractions between one atom’s + nucleus and
the other atom’s – electrons and the proton-proton
repulsions as well as electron-electron repulstions.
5 • Chemical Bonding: Gen Concepts
The Covalent Bond
PE
Attractions and Repulsions
(5 of 12)
Distance between nuclei
If two atoms have half-filled orbital s , the interactions
–
balance at a small enough distanc e so the e
’s can be close
to both nucle i at the same time... this is a covalen t bond.
Count up your valence electrons.
Give every atom who “wants” and octet an octet.
[the first 5 elements do not need octets... too small]
[Family I, II, and III do not form octets]
5 • Chemical Bonding: Gen Concepts
Groves’ Electron Dot System
If you have drawn too man y electrons...
Multiple & Extended Valence Bonds
“Take away a lone pair... take away a lone pair...
(6 of 12)
make these two atoms share”
If you have drawn too fe w electrons... place the extra
electrons on the central atom (extended valence shell)
Bond orde r is the number of pairs of electrons bonding two
atoms together.
single bond
bond order = 1
double bond
bond order = 2
triple bond
bond order = 3
5 • Chemical Bonding: Gen Concepts
single bonds have the longest bond length
Bond Order: Bond Length, Strength, &
single bonds have the weakest bond strength
Vibrational Frequency
single bonds have the lowest vibrational frequency
(7 of 12)
(think of single bonds as soft, springy springs...
triple bonds are tight springs...sproinnnnng)
Bonds in resonance structure must be averaged... the S-O
2–
bond in SO
has a bond order of 1.5. C-O in CO
is 1.33
2
3
2–
When you draw a Lewis structure (SO
, O
, CO
, etc.) in
2
3
3
which you must make a choic e as to who gets a double
bond, the structure is actually a blend of two or three
structures.
5 • Chemical Bonding: Gen Concepts
We “say” that the structure “resonate s ” or we say that the
Resonance
structure contains contributions from each of the resonance
(8 of 12)
structures.
Resonance occurs simply because the electron-dot model
(while very useful) is too limited to show how the electrons
are being shared between the atoms... wait for π bonding.
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