Homework #11, Graded Answers
Chem20, Elementary Chemistry
10.48) Write a Lewis structure for each of the following.
(A) CH4
Total: (1)(4 e- ) + (4)(1 e- ) = 8 total eUsed: 4 bonds x (2 e- ) = 8 used eNeeded: 0
8 total – 8 used – 0 needed = 0  structure is correct
H
H
C H
H
(B) NF3
Total: (1)(5 e- ) + (3)(7 e- ) = 26 total eUsed: 3 bonds x (2 e- ) = 6 used eNeeded: 20 needed e26 total – 6 used – 20 needed = 0  structure is correct
..
: F:
.. N ..
:F .. F :
..
..
(C) OF2
Total: (1)(6 e- ) + (2)(7 e- ) = 20 total eUsed: 2 bonds x (2 e- ) = 4 used eNeeded: 16 needed e20 total – 4 used – 16 needed = 0  structure is correct
..
.. O ..
:F.. .. F
.. :
(D) H2O
Total: (2)(1 e- ) + (1)(6 e- ) = 8 total eUsed: 2 bonds x (2 e- ) = 4 used eNeeded: 4 needed e8 total – 4 used – 4 needed = 0  structure is correct
..
O
..
H
H
10.50) Write a Lewis structure for each of the following.
(A) N2O (oxygen is terminal)
Total: (2)(5 e- ) + (1)(6 e- ) = 16 total eUsed: 2 bonds x (2 e- ) = 4 used eNeeded: 16 needed e16 total – 4 used – 16 needed = -4/2  2 multiple bonds
..
..
..
N
.. N O
:
.. or N
.... N O:
(B) SiH4
Total: (1)(4 e- ) + (4)(1 e- ) = 8 total eUsed: 4 bonds x (2 e- ) = 8 used eNeeded: 0
8 total – 8 used – 0 needed = 0  structure is correct
H
H
Si H
H
(C) CI4
Total: (1)(4 e- ) + (4)(7 e- ) = 32 total eUsed: 4 bonds x (2 e- ) = 8 used eNeeded: 24 needed e32 total – 8 used – 24 needed = 0  structure is correct
..
: I:
..
..
: I.. C ..I :
:..I :
(D) Cl2CO (carbon is central)
Total: (2)(7 e- ) + (1)(4 e- ) + (1)(6 e- ) = 24 total eUsed: 3 bonds x (2 e- ) = 6 used eNeeded: 18 needed e24 total – 6 used – 18 needed = -2/2  1 multiple bond
..
: O:
: O:
.. C ..
.. C ..
Cl
Cl
: Cl
:
Cl
.. :
.. or ..
..
10.52) Write the Lewis structure for each molecule.
(A) H2CO
Total: (2)(1 e- ) + (1)(4 e- ) + (1)(6 e- ) = 12 total eUsed: 3 bonds x (2 e- ) = 6 used eNeeded: 8 needed e12 total – 6 used – 8 needed = -2/2  1 multiple bond
:O :
C
H
H
(B) H3COH
Total: (4)(1 e- ) + (1)(4 e- ) + (1)(6 e- ) = 14 total eUsed: 5 bonds x (2 e- ) = 10 used eNeeded: 4 needed e14 total – 10 used – 4 needed = 0, structure is correct
H H
H C
H
..O..
(C) H3COCH3
Total: (6)(1 e-) + (2)(4 e- ) + (1)(6 e- ) = 20 total eUsed: 8 bonds x (2 e- ) = 16 used eNeeded: 4 needed e20 total – 16 used – 4 needed = 0, structure is correct
H H
H
C
H
C H
..O..
H
(D) H2O2
Total: (2)(2 e- ) + (2)(6 e- ) = 14 total eUsed: 3 bonds x (2 e- ) = 6 used eNeeded: 8 needed e14 total – 6 used – 8 needed = 0, structure is correct
..
O H
.. ..
H O..
10.54) Determine what is wrong with each Lewis structure and write the correct structure.
(A) H has too many bonds (can only have one maximum).
..
(B) Each Cl atom has too many bonds (holding 10 total electrons).
.. ..
(C) Carbon isn’t getting a full octet (3 bonds = 6 total electrons)
: :
..
..
(D) Too many bonds to H (one bond maximum).
..
.. :
10.58) Write a Lewis structure for each ion, including resonance if necessary.
(A) SO42Total: (1)(6 e- ) + (4)(6 e- ) + 2 e- = 32 total eUsed: 4 bonds x (2 e- /bond) = 8 used eNeeded: 6 per O atom = 24 needed e32 total – 8 used – 24 needed = 0
..
: :
..
..
:
: ..
..
: :
..
(B) HSO4Total: (1)(1 e- ) + (1)(6 e- ) + (4)(6 e- ) + 1 e- = 32 total eUsed: 5 bonds x (2 e- /bond) = 10 used eNeeded: 6 for 3 O atoms, 4 for O atom = 22 needed e32 total – 10 used – 22 needed = 0
..
: :
..
..
:
..
..
: :
..
(C) NH4+
Total: (1)(5 e- ) + (4)(1 e- ) – 1 e- = 8 total eUsed: 4 bonds x (2 e- / bond) = 8 used eNeeded: 0 e8 total – 8 used – 0 needed = 0
(D) BrO2-
Total: (1)(7 e- ) + (2)(6 e- )+ 1 e- = 20 total eUsed: 2 bonds x (2 e- / bond) = 4 used eNeeded: 6 e- per O, 4 e- per Br = 16 needed e20 total – 4 used – 16 needed = 0
.. .. ..
..
:
.. :
..