Transcript Chemistry Notes Bond Polarity Molecular Polarity Intermolecular Attractions Types of Bonds Up until now, we have assumed that there are two types of bonds: Covalent and.

Chemistry Notes
Bond Polarity
Molecular Polarity
Intermolecular Attractions
Types of Bonds
Up until now, we have assumed
that there are two types of
bonds: Covalent and Ionic.
 This is true, but covalent bonds
can be broken into two
categories

Nonpolar Covalent
 In
nonpolar covalent bonding
electrons are shared equally.
 Electrons spend an equal
amount of time with both
elements in the bond.
 Typical in diatomic elements:
H2, N2, O2, F2, Cl2, Br2, I2
Polar Covalent
 In
polar covalent bonding, electrons
are still shared, but they are shared
unequally.
 This is due to one nucleus pulling
the shared pair harder than the other.
 This creates a dipole—a bond where
one side is slightly positive and the
other is slightly negative.
Polar Covalent
A
dipole is caused because the
electron spends more time on
one side than the other.
 The polarity of the bond is
shown like:
H—Cl
OR
d+
d-
H—Cl
Ionic Bonds
 In
an ionic bond, electrons
are transferred.
 The nucleus of one element
pulls hard enough to take
electrons away completely.
How can you tell what kind of
bond there is?
 By
looking at the difference in
electronegativity!
 Remember, electronegativity is the
tendency of an atom to attract an
electron when bonding.
 The more electronegative, the more
it will pull electrons.
Nonpolar Bonds:
EN Diff ≤ 0.4
Polar Bonds:
0.4 < EN Diff ≤ 1.7
Ionic Bonds:
EN Diff > 1.7
What type of bond is between:
H
and Cl
Li and Cl
C and S
F and O
What type of bond is between:
N
and Br
Na and F
C and O
Polar Molecules
 If
the slightly positive and
slightly negative ends of
polar bonds can collect on
two different sides of a
molecule, it can make an
entire molecule polar.
Polar Molecules
 If
bonds are nonpolar, a
molecule will always be
nonpolar.
Polar Molecules
 If bonds are polar and the shape
of a molecule is symmetrical, the
molecule will usually be
nonpolar because the charges
pull against each other and
cancel out.
 CO2
Polar Molecules
 Linear,
trigonal planar, tetrahedral
and trigonal bipyramidal are the
symmetrical shapes we talked
about.
 If
the bonds are polar and
the molecule has a positive
side and a negative side, the
molecule will be polar, even
if it is a symmetrical
molecule.
 HF
Polar Molecules
 If bonds are polar and the
molecule is asymmetrical,
the molecule will be polar!
 (Bent and pyramidal
molecules are
asymmetrical)
 H2O and NH3
Attractions between molecules
 They are what make solid and
liquid molecular compounds
possible.
 The weakest called van der
Waal’s forces - there are two
kinds:
Dipole interactions



Occur when polar molecules are attracted to
each other.
Slightly stronger than dispersion forces.
Opposites attract but not completely hooked
like in ionic solids.
+
d
d
H F
+
d
d
H F
Dipole Interactions
+
d
d+
d-
d
Hydrogen bonding
 Are
the attractive force caused by
hydrogen bonded to F, O, or N.
 F, O, and N are very electronegative.
 The strong dipole forms when
Hydrogen is bonded with one of the
very electronegative elements above.
Hydrogen bonding
 The
hydrogen partially share with
the lone pair in the molecule next
to it.
 The strongest of the
intermolecular forces.
Hydrogen bonding
 When
a hydrogen is covalently bonded
to a highly electronegative atom, AND
is also weakly attracted to an unshared
electron pair of another EN atom.
The hydrogen is left very electron
deficient, thus positive, so it
attracts with any nearby negative
charge
Hydrogen Bonding
d+ dH O
+
Hd
Hydrogen bonding
H O
H