GOOD MORNING!
Today we will:
Turn Covalent Bond Practice Problems & Quiz Revisions
• Ionic/Covalent Naming Quiz
• Continue Lewis Structures
– Atoms
– Ions
– Molecules
• Start Practicing!
• HW: DUE Fri 2/12 Start Lewis Practice Problems
• 2nd Column of Vocab DUE Fri
Who the Heck is Gilbert Lewis?
Ba:
.
:
• Lewis devised a method for showing how
electrons are arranged in elements and
compounds.
• He used element symbols to represent atoms
and dots to show the valence electrons in a structure.
• We call them “Lewis Dot Structures” or “Lewis
Dot Diagrams” or just “Lewis Structures”
• Some examples:
:P:
:O:
Lewis Diagrams / Structures
Lewis structures represent electron distribution
in atoms, ions, and molecules by showing ALL
valence electrons
•Atoms Ba:
•Ions
[Na]+ ,
•Molecules
•Polyatomic ions
or
Lewis Structures for Atoms and Ions
Write the symbol of the atom and show a dot
for each valence electron.
Si
Write the symbol of the ion, show a dot for each
valence electron ADDING electrons for a (-)
ion and SUBTRACTING electrons for a (+) ion.
[Al]+3
[:Ö̤ :]-2
Put brackets [ ] and a charge on the symbol.
Lewis Structures for Ionic Compounds
: :
: :
• Arrange ions symmetrically based on charge
• Show valence electrons around each atom
representing e-’s lost and gained in bonding
(none for metals and full octet for nonmetals)
• Put brackets and charge on each ion
Example: MgBr2
[:Br:]- [Mg]2+ [:Br:]-
Lewis Structures for Molecules
• Goal: every atom has full octet (8 electrons)
• Use the trial and error method of counting valence
electrons and distributing them, in pairs, to achieve octet
(each atom has 8 e-)
• Or, use need / have / share method to determine number
of bonds first, then distribute e-’s to achieve octet
• Keep e-s in pairs!!!
• Only include double or triple bonds if necessary
• Exceptions to octet rule:
H only gets 2 e-s
Be only gets 4 e-s
B and Al only get 6 e-s
Total e-’s = odd number
e-’s on atom exceed 8
Lewis Structure Helpful Hints
• Carbon is the middle man, (4 bonding e- pairs)
• H is always on perimeter, (1 bonding e- pair)
• Halogens share 2 e-’s (one bonding e- pair)
• Oxygen: share 4 e-’s (2 bonding e- pairs)
• Nitrogen: share 6 e-’s (3 bonding e- pairs)
Rules are meant to be broken … except C and H!
CH3OH
CHOCl
NI3
What would Lewis do?
Write a Lewis Structure for the following
molecules:
•OBr2
•CH2F2
•CF2O
Describe the electron arrangement on the central
atom
• # of unshared e- pairs,
• # of shared e- pairs (single, double, triple
bonds)
Lewis Structures for Polyatomic Ions
• Anions: anions are negative ions because they
have more electrons than protons
ADD electrons to equal the charge
• Cations: cations are positive ions because they
have less electrons than protons
REMOVE electrons equal to the charge
ClOPO43-
Write a Lewis Diagram for each of the following and
identify the shape
• PCl3
• CH2Br2
• CH2O
• BrO3• C2H4