covalent bonding sharing of electron pairs non-metal with non-metal atoms
TRANSCRIPT
Covalent Bonding
Sharing of Electron Pairs
Non-metal with Non-metal Atoms
Covalent Bonding
Like ionic bonds, covalent bonds are +/- attractions.
Closed-shell considerations often explain the patterns of bonding, i.e., the formulas -- just as for ionic systems
H2
He-
He-
Neutral atomsPush ‘em together...
H2
He-
He-
Equivalent to:
H : H
The pair of shared electrons
Negative shared electronsPositive nuclei
H + C
1H1e-
6C2e-
4e-Equivalent to:
H· ·C ··
·Outer e- only shown
H + C
H· ·C ··
·
Outer e- only shown
H·
H·
H·
H + C
C
Outer e- only shown
H
:HH: ::H 2 e- at each H
8 e- at carbonall atoms closed shell
Positive nuclei
Negative electrons
H + N
H·
Outer e- only shown
H·
H·N ··
·:
H + N
N
Outer e- only shown
H
:HH: :: 2 e- at each H
8 e- at nitrogenall atoms closed shell
H + O
H·
Outer e- only shown
H·
O :·
·:
H + O
O
Outer e- only shown
H
:H: :: 2 e- at each H
8 e- at oxygenall atoms closed shell
H + F
Outer e- only shown
H·
: F :·
:
H + F
F
Outer e- only shown
H
: : ::
2 e- at H
8 e- at fluorineall atoms closed shell
Patterns for Major Elements
CH4 C = 4 bonds; all electrons shared
NH3 N = 3 bonds; one lone pair
H2O O = 2 bonds; two lone pairs
HF F = 1 bond; three lone pairs
4 BondsAll e-
shared
3 Bonds1 Lone Pair
2 Bonds2 Lone Pairs
1 Bond3 Lone pairs
• Carbon, group IV
• Nitrogen, Group V
• Oxygen, Group VI
• Fluorine, Group VII
Other Compounds Have Same Pattern
C = 4 bonds; Cl (like F) = 1 bond
P (like N = 3 bonds; Br (like F) = 1 bond
More Similarities:
S (like Oxygen) = 2 bonds, 2 lone pairs
C = 4 bonds; O = 2 bonds, 2 lone pairs
Multiple Bonds
Atoms may share more than one pair of electrons
a DOUBLE BOND forms when atoms share two pairs of electrons (4 e-)
a TRIPLE BOND forms when atoms share three pairs of electrons (6 e-)
Total number of bonds per atom unchanged
Multiple Bonds
4 Bonds, each carbon
Two bonds at oxygen
•C2H4 Valence e- = 12
•H2CO Valence e- = 12
Multiple Bonds
Total valence e- = 16 (Oxygen = 6 e-, each;
Carbon = 4 e-. Four bonds/C; 2 bonds oxygen
Total valence e- = 10 (H=1, C=4, N=5)Bonds: C=4, N=3, H=1
Total valence e- = 18 (O=6, Cl = 7, P = 5)Bonds: Cl=1, P=3, O=2
Predicting Dot DiagramsHow Do We Proceed?How Do We Proceed?
• Determine total number of valence electrons• Based on usual bond nos., identify reasonable
layout for atoms• Place bonding electrons between atoms to
make usual no. of bonds• Place remaining electrons as lone pairs around
atoms still lacking an octet
Total number of Valence e-
Sum of group numbers for atoms of representative elements
Eg., C = 4e- N = 5e- O = 6e- H = 1e-
CCl4 = 4e- + (4 x 7e-) = 32e-
SO2 = 6e- + (2 x 6e-) = 18e-
N2H4 = (2 x 5e-) + (4 x 1e-) = 14e-
C3H8 = (3 x 4e-) + (8 x 1e-) = 20e-
Reasonable LayoutsBased on Covalence (Usual Bonds) Nos.Based on Covalence (Usual Bonds) Nos.
•H2S -- 1 Bond each H; 2 Bonds for SH-H=S Incorrect - One H has 3 bondsH-S-H Correct - All atoms with usual
bond numbers (H=1; S=2)•PCl3
Cl=P-Cl-Cl Incorrect - One Cl has two bonds
Cl-P-Cl Correct -- (Cl=1; P=3) |
Cl
Practice
OFOF22
Layout:
O-F-FO-F-F
Layout:
O-F-FO-F-F Incorrect -- One F with two bonds; O only one bond
Layout:
O=F-FO=F-F
Layout:
O=F-FO=F-F Incorrect -- One F with three bonds; (O does have two bonds)
Layout:
F-O-FF-O-F
Layout:
F-O-FF-O-F Correct -- F = 1 bond, each; O = 2 bonds)
Practice
Place bonding electrons for connected atoms
Practice
Place bonding electrons for connected atoms
Practice
Add lone pairs for atoms needing “octet”
Practice
Add lone pairs for atoms needing “octet”
Practice
Similarly, add lone pairs for fluorines:
Practice
Check Results!
• Correct total e- (O = 6; F = 7, ea) = 20e-
• Usual bond nos. (O=2; F=1, ea)• Closed shell (octets) O=8; F=8 each
Now You Do One:
CHCH22ClCl22
Total e-
C = 4 e-
H = 1e-, each, 2 total Cl = 7e-, each = 14 more Grand total = 20e-
Layout:
H-H-C-Cl-ClH-H-C-Cl-Cl
Layout:
H-H-C-Cl-ClH-H-C-Cl-Cl IncorrectIncorrect
Layout:
H-C-Cl-Cl-HH-C-Cl-Cl-H IncorrectIncorrect
Layout:
H-H-Cl=C=ClH-H-Cl=C=Cl IncorrectIncorrect
Layout:
Correct!Correct!C
H
H Cl
Cl
Check Results:
• Total eTotal e--
• Usual no. BondsUsual no. Bonds• Closed ShellsClosed Shells
And Another
OCSOCS
Number e-
C = 4eC = 4e--
O = 6eO = 6e--
S = 6eS = 6e--
Total = 16eTotal = 16e--
Layout?
O C SO C S
oror
C S OC S O
oror
S O CS O C
????
Layout
O=C=S
2 Bonds for O; 4 Bonds for C; 2 Bonds for S
Great!Great!