Transcript Lewis Structures

Covalent Lewis Structures
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Add up the valence electrons.
Put the element with the fewest number of atoms in the
middle and surround with the remaining elements.
Draw a line from the central atom to the adjacent atoms
Subtract two electrons for each line drawn.
Make octets as needed giving the most electronegative
atoms electrons first. B only needs 6, H &He 2 e’s. P, S,
Cl, Argon and everything below can violate the octet
rule and have more than 8 e’s if you must.
If needed form double and triple bonds.
Assign formal charges to atoms.
Formal Charge = # of valence electrons – (# of dots+ # of lines)
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Assign formal charges to molecules.
VSEPR
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Beryllium chloride
Aluminum chloride
Methane (CH4)
Phosphine (PH3)
Water
Niobium (V) Bromide
Sulfur hexafluoride
Notes
Water
CO2
CO
BeCl2
AlCl3
CH4
PH3
H2O
NbBr5
SF6
C2H3O2-1
HNO3
CO3-2
PO4-3
ClO2-1
Na2SO3
CN-1
(NH4)2O2
SeF6
NCl3
I2S
SiO2
BF3
PI5
CCl4
BeCl2 (Ionic)
AlCl3 (Ionic)
CH4 (Covalent)
PH3 (Covalent)
H2O (Covalent)
NbBr5 (Ionic)
SF6 (Covalent)
HCl
Rb2S
PI3
SiCl4
O3
C2H2
N2
O2
I2 O
TeO4-2
BI3
SeS2
SbCl5
NO3-1
TeCl6
AsO4-3
H2 S
SiI4
BBr3
SiO
PCl5
NCl3
TeF6
CaO
TlAt3
SrCl2
PbCl4
SbI5
Rb2O
NaF
RaBr2
Al2O3
the total number of atoms present.
Exception: if the compound is negatively charged, add 1 electron for each negative value
Exception: if the compound is positively charged, remove 1 electron for each negative
value
Example: CH4 C= 4 VE H= 1VE = 4 + 4(1) = 8 EA
Example: CO2
Example: SO42Draw out a skeletal arrangement of lewis structure. Place the least electronegative atom in
the center, surrounded by the remaining atoms. Draw lines to represent the bonds between
the central atom and each surrounding atom.
Exception: Hydrogen can never be a central atom because it is found in the first energy
level and can only have 2 electrons at most.
Draw the skeletal arrangement in the following examples
CO2
H2SO4 (Just underline the central atom)
NCl3
PF5
Count and draw in the number of electrons necessary (EN) for each to have a full octet.
These are the electrons needed. Be sure to include the bonded electrons.
Example: CO2
Subtract the number of valence electrons available (from step one) from the number of
electrons needed (EN –EA). This is the number of valence electrons that you still need. We
make up for these by adding double or triple bonds. If you get a negative number, you have
extra electrons. These may become part of your expanded octet.
Example: CO2
To add double or triple bonds: divide the number you get from step 4 by 2 (why? Because