Lewis Structures,
Molecular Geometry,
Polarity, Intermolecular
Forces
Kelly Franks, Juliet Hurvich , Lauren Cunningham
LEWIS
STRUCTURES
Key Terms & Tips:
➔ The pair of dots between two symbols represents the shared pair of a
covalent bond.
➔ Each fluorine atom is surrounded by three pairs of electrons that are
not shared in bonds.
➔ An unshared pair, also called a lone pair, is a pair of electrons that is
not involved in bonding and that belongs exclusively to one atom.
➔ Covalent Bonds are represented by dashes
➔ Valence Electrons: the outer level of electrons
➔ Resonance Structure: one of two or more Lewis structures for a single
molecule can be drawn to represent a molecule
Lewis Structure Steps:
1. Draw skeletal structure of compound showing what atoms are
bonded to each other. Put least electronegative element in the
center.
2. Count total number of valence e-. Add 1 for each negative charge.
Subtract 1 for each positive charge.
3. Complete an octet for all atoms except hydrogen
4. If structure contains too many electrons, form double and triple
bonds on central atom as needed.
DRAW, COUNT, COMPLETE, FORM
Examples:
1. NF3
2. H2O
Answers:
Water
Nitrogen Trifluoride
MOLECULAR
GEOMETRY
Definitions
VESPR Theory (Valence eletrron shell pair
repulsion) -- used to predict the shape of
individual molecules based upon the
extent of electron-pair electrostatic
repulsion
Sample Problems:
1. Identify the name and shape of the bond
angles of perchlorate.
2. Identify the name and shape of the bond
angles of phosphorus fluoride.
Answers:
1. Tetrahedral, 109.5 degrees
2. trigonal bipyramidal, 120 and 90 degrees
Polarity
Definitions:
● Polarity-- how equal bonding electrons are
shared between elements
● Polar Bond or Polar Covalent Bond-covalent bond with greater electron
density around one of the two atoms
● Electronegativity-- the ability to attract
electrons
Determining Type of Bond
● If the difference in electronegativities
between atoms is:
○
0 to .3 = nonpolar covalent bond
○ .4 to 1.7 = polar covalent bond
○ greater than 1.7 = ionic bond
Properties of Covalent Bonds
●
●
●
●
usually soft and squishy
not soluble in water
can’t conduct electricity
low melting/boiling point
Properties of Ionic Bonds
●
●
●
●
●
hard and brittle
tightly packed solids in a crystal lattice
usually soluble in water
conducts electricity when dissolved
high melting points
Questions
1) Classify NaCl as ionic, nonpolar covalent,
or polar covalent.
2) Classify PCl3 as ionic, nonpolar covalent,
or polar covalent.
Answers
1) ionic
2) polar covalent
Intermolecular
Forces
Key Terms & Tips:
•
•
•
Intermolecular Force- attractive force
between molecules
These forces hold atoms together
If you have one type of force, you
automatically have all the forces weaker
than that one
Forces Weakest to Strongest:
1. London Dispersion Forces
2. Dipole-Induced Forces
3. Dipole-Dipole Forces
4. Hydrogen Bonds
London Dispersion Forces
•
•
•
also called Van Der Waals Forces
attractive forces between 2 nonpolar
molecules
very brief interaction
Dipole-Induced Forces
•
•
also called dispersion forces
attractive forces that arise as a result of
temporary dipoles induced in atoms or
molecules
Dipole-Dipole Forces
•
•
attractive forces between polar molecules
oppositely charged ends of the molecules
will attract each other
Hydrogen Bonds
•
•
hydrogen of one molecule attracted to the
directly connected oxygen, nitrogen, or
fluorine of another
special kind of dipole-dipole bond
Ion-Dipole Forces
•
•
attractive forces between an ion and a
polar molecule
need to be 2 different types of molecules
Questions:
1. Which of these molecules is capable of
forming a hydrogen bond?
a.
MgO
b. HF
c. HCl
d. NaF
2. What is the strongest intermolecular force
in the molecule HCl?
3. What type of force is acted on CH4?
Answers
1. b. HF
2. dipole-dipole
3. London Dispersion
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