Download 12-3: Lewis Structures

12-3: Lewis Structures
 Bonding only involves valence electrons
 Lewis structures—represent valence electrons; use dots placed
around the chemical symbol
 All atoms want to achieve a noble gas configuration
o Octet Rule—most elements will be surrounded by 8 dots,
representing noble gas configuration
 Hydrogen is full with 2 electrons (2 dots on one
side)—so it is like helium
Draw the Lewis structures for:
H
Ca
N
F
Ar
 Ionic compounds: draw dots showing where electrons would be
after transfer, plus resulting charges
 Molecules: draw shared electrons as shared dots
o A shared pair of electrons can be drawn as a line,
representing a bond. (Bonding Pair)
 The other electrons that are not shared are called unshared
pairs or lone pairs
Draw Lewis structures for compounds made from these elements:
H and Cl
Ca and F
H2
Cl2
 Single Bond—sharing one pair of electrons (Ex: NH3)
 Double Bond—sharing two pairs of electrons (Ex: CO2)
 Triple Bond—sharing three pairs of electrons (Ex: C2H2)
Finding the Number of Bonds in a Compound:
# e- each atom wants to have (noble gas config…)
MINUS
# e- ea. atom actually has (see atomic #...)
DIVIDE (this difference) BY 2
= the # of covalent bonds in the compound
o Don’t forget unshared pairs! Double Check!!
 Some compounds show resonance**
o No single structure accurately represents the electron
location. (Ex: Benzene, ozone, carbonate ion)
 Polyatomic Ions:
o Negative—add that # of eo Positive—subtract that # of e Draw, then add brackets and charge
 Try drawing: PO43-
 Exceptions to the Octet Rule
o Compounds with an odd number of valence electrons
 BF3, SF4, NO, NO2, etc