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Chemistry LibreTexts

Solutions

For each molecule on the worksheet, the Lewis Dot Structure, the number of valence electrons, the electron arrangement (E.A.) and the molecular geometry (M.G.) are given, respectively.  To see a larger view of the Lewis Dot Structure, point at the molecule, right click on the mouse and go to 'View image'.

Lewis Dot works best for covalent compounds of group A elements, though Lewis Dot Structures can explain electron transfer in ionic compounds. By following the rules below, the Lewis Dot Structure can be written for covalent compounds and some polyatomic ions.

  1. Count the total number of valence electrons, adjust for charge if an ion.  Add one electron for each negative charge, subtract one electron for each positive charge.
  2. Place a pair of electrons between the central atom (usually written first) and each of the outer atoms.
  3. Complete the octet of the outer atoms (except H, which needs only 2 electrons).
  4. Place extra electrons, if any, on the central atom in pairs.
  5. If the central atom does not have a complete octet, share extra electrons from the outer atoms until the central atom and the outer atoms have a complete octet.  Note: halides do not form double bonds.

 

PF5 40 electrons
tbp
tbp
CS2 16 electrons
linear
linear
BrO3- 26 electrons
Td
trigonal pyr.
           
NH4+
8 electrons
Td
Td
SCl4 34 electrons
tbp
see-saw
BrF5 42 electrons
Oh
square pyr.
           
BF3
24 electrons
trigonal planar
trigonal planar
SCl6 48 electrons
Oh
Oh
PH3
8 electrons
Td
trigonal pyr.
           
NF3
26 electrons
Td
trigonal pyr.
SO42-
32 electrons
Td
Td
CO32- 24 electrons
trigonal planar
trigonal planar
           
SiCl4 32 electrons
Td
Td
ClO3- 26 electrons
Td
trigonal pyr.
CH2O 12 electrons
trigonal planar
trigonal planar
           
NO3-
24 electrons
trigonal planar
trigonal planar
 O3
18 electrons
trigonal planar
bent
CCl4 32 electrons
Td
Td
           
AlH3
6 electrons
trigonal planar
trigonal planar
 SO2 18 electrons
trigonal planar
bent
SO3 24 electrons
trigonal planar
trigonal planar
           
CO
10 electrons
linear
linear
CHCl3 26 electrons
Td
Td
BrF3 28 electrons
tbp
T-shaped
           
H2S
8 electrons
Td
bent
I3- 22 electrons
tbp
linear
H3O+
8 electrons
Td
trigonal pyr.