Do Now:
What are the three types of bonds?
Compare them.
Which compounds contain
which bonds?
Why?
•Properties of metals?
High electrical and thermal conductivity,
luster (shiny), malleable, ductile
Metallic Bond
Valence electrons are delocalized. The bond
results from the electrostatic attraction between
the delocalized electrons and the metallic ions.
Positive ions
(cations) in a "sea"
of delocalized
electrons.
Ionic Bond
•Transfer of electrons
•Metals lose elelctron(s) to form positive ions
(cations)
•Nonmetals gain electron(s) to form negative
ions (anions)
Li
Lower IE
:
:
Li. :Cl:
.
+
-
:Cl:
..
More negative EA
Ionic Compounds
•Properties???
Brittle, crystalline substances
with high melting points,
most soluble in water,
conduct electricity when
melted and in solution,
Lattice Energy
Molecular Compounds - Covalent Bonding
• Gas, Liquid,Solid with generally low melting points,
brittle, do not conduct electricity
• Looking at hydrogen molecule, H2
• High electron density between nuclei. The atoms
are held together because the two positive nuclei
are attracted to the concentration of negative
charge between them. The shared
pair in a covalent bond acts as “glue”
Lewis Structures
• Use Lewis Dot Diagrams
• Lone pairs (nonbonding pairs – unshared)
• Bonding Pairs –shared between two nuclei
Draw Lewis structures for N2, O2, and F2
•Compare bond length and bond enthalpy,
enthalpy change DH to break bond
•Estimate DH for synthesis of ammonia
Energy Calculations
•Estimate DHfo for potassium chloride provided
with:
•Lattice energy of KCl: -690 kJ/mol
•First IE for K: 419 kJ/mol
•Electron affinity of Cl: -349 kJ/mol
•Bond Energy of Cl2: 239 kJ/mol
•Enthalpy of sublimation for K: 64 kJ/mol
Ionic and Covalent Bond are on the extremes,
what about HCl
•Polar covalent bond
•Dipole moment – measure of is the
measure of net molecular polarity, tell us
about the charge separation in a molecule.
Electronegativity – ability of atom to
attract electrons. Explain trend
What type of bond exists between…
•H and O
•S and S
•Li and Cl
-
Lewis Structures
•Type of structural formula that uses dots
or dashes to indicate bonds
Bromine molecule, Br2
Water, H2O
Ethyne, C2H2
Methane, CH4
DO NOW
•Draw the Lewis Structure for NCl3
and HCN
•Indicate the shared and unshared
pairs of electrons
•What is another term for shared
electrons?
alence
V
hell
S
lectron
E air
P epulsion
R
This theory states that pairs of valence
electrons are arranged as far apart from each
other as possible
Draw Lewis Structures for
• H2, C2H2, BH3, NH3, H2O, PCl5, SF6
• In the last two examples, will you satisfy the octet rule? Explain
Example
Shape
Angle
H2 and C2H2
Linear
180º
BH3
Trigonal Planar
120º
Methane
Tetrahedral
~109.5º
?
Ammonia
Trigonal Pyramidal
~107º
Water
Bent (V-shaped)
~104.5º
Phosphorus
Pentachloride
Trigonal
Bipyramidal
90º, 120º
Sulfur
hexafluoride
Octaheral
90º
A molecule’s attractive forces impacts its
melting and boiling points as well as many other
properties.
•Will a molecule that is highly attracted to
another molecule of its kind have a high
boiling point or a low boiling point? In
which state will the substance typically be
found at room tempterature?
First let’s review: Distinguish
between polar and nonpolar bonds.
What do those terms mean and how
do you make this determination?
Polarity of Molecule
•Polar Molecule (Dipoles) – have a positive
end and a negative end
•Nonpolar Molecule - has an equal
distribution of electrons and therefore no
positive or negative ends
Polar or Nonpolar Molecules…
•H2
•CO2
•H2O
Shape of molecule and polarity of
bonds determines polarity of molecule.
Valence Bond Theory
• Covalent bonds form when a pair of electrons is shared by overlapping
atomic orbitals on adjacent atoms.
Consider HF, draw the valence electron
configuration for H and F
X __
X __
2p __
X
H 1s__
F 2s__
Methane, CH4
•Draw the valence electron configuration
for C and H
Carbon’s four sp3
hybrid orbitals
Add four hydrogen
s orbitals
Boron Trihydride, BH3
•Draw the valence electron configuration
for B
Boron’s three sp2
hybrid orbitals, has
1 empty p orbital
Add three
hydrogen s
orbitals
Ethyne, C2H2
•Draw the valence electron configuration
for C
Each carbon has two sp orbitals and two p orbitals
Add two
hydrogen s
orbitals
• Sigma (s) bond – results from end to end overlap of atomic orbitals
• Pi (p)bond – side be side overlap of atomic orbitals
Try C2H4
Which bonds are s? p?
Summary of Valence Bond Theory
Hybridization VSEPR theory shape
Example
sp
Linear (2)
C 2H 2
sp2
Trigonal planar ( 3)
BH3
sp3
Tetrahedral, bent
(2 shared, 2 unshared),
pyramidal (4)
CH4
sp3d
sp3d2
Trigonal bipyramidal (5)
PCl5
Octahedral (6)
SF6