Transcript Types of Covalent Bonds

Bond Types
Let’s Look
At 3 Types of Bonds
• Ionic
• Polar Covalent (Molecular)
• Nonpolar Covalent
(Molecular)
Remember Electronegativity?
• The tendency for an atom to attract
electrons to itself in a bond
– The higher the value, the better it is at
attracting electrons.
• The difference in the
electronegativity values determines
what type of bond will be formed.
Electronegativity
Electronegativity is a scale from 0.7 (Cs) to 4.0 (F).
Electronegativity
generally
increases across a
period and
decreases down a
group.
Electronegativity Values
(these will be given to you)
• Why don’t
the noble
gases have a
value?
• They don’t
attract
electrons!
Ionic Bonds
• If the electronegativity difference is greater
than 1.7, one atom will pull the electron
completely away from other atom.
•
•
•
•
The electrons are NOT shared.
An Ionic Bond is formed as + and – attract.
Electronegativity of Na is 0.9; Cl is 3.0.
3.0 – 0.9 = 2.1; difference >1.7, so…Ionic!
Polar Covalent Bonds
• Covalent bonds share electrons
• The shared pairs are pulled, similar to a
tug-of-war, between the nuclei of the atoms
sharing the electrons.
• If the electronegativity difference is
between 0.3 – 1.7, one side of the bond
becomes slightly more negative and the
other side becomes slightly more positive.
• This is a Polar Covalent Bond.
Polar Covalent Bonds
Slightly
∂+
∂H
Cl
• The electronegativity of H is 2.1; Cl is 3.0.
• 3.0 – 2.1 = 0.9; difference is b/w 0.3 – 1.7,
so…Polar Covalent!
Polar Covalent Bonds
• The electronegativity of O is 3.5; H is 2.1.
• 3.5 – 2.1 = 1.4
• Difference is b/w 0.3– 1.7, so… Polar Covalent!
Nonpolar Covalent Bonds
• When the atoms have equal pull, causing the
electrons to be equally shared, the bond is
Nonpolar Covalent.
• Neither side of the bond is even slightly positive or
negative.
• The electronegativity difference is b/w 0.0 – 0.3.
• This is the type of bond that occurs between 2
atoms of the same element. (H2, O2, Cl2, etc.)
Nonpolar Covalent Bonds
• The electronegativity of H is 2.1.
• 2.1 – 2.1 = 0
• The difference is b/w 0.0 – 0.3, so…Nonpolar!
3 Different Types of Bonds
Attractions Between Molecules
Van der Waals Forces
• Weaker than either the ionic or covalent bonds
that form between atoms in a compound.
• Responsible for determining whether a compound
is a liquid, gas, or solid
• 3 basic types from weakest to strongest
– (London) Dispersion forces
– Dipole interaction
– Hydrogen bonding
London Dispersion Forces
• Weakest of all molecular attractions
• Caused by the motion of electrons producing
a temporary polarity.
• Strength of dispersion forces generally
increases as # of electrons in the molecule
increases.
• All molecules have these weak attractions.
London Dispersion Forces
Dipole Interaction
• Occurs when polar molecules are
attracted to one another
Hydrogen Bonds
• Occurs b/w molecules in which H is
covalently bonded to either O, N, or F,
which are very electronegative
– Causes very polar molecules that are
strongly attracted to each other
– Still only has about 5% of the strength
of a covalent bond
Very Important!!
• Reason ice is
less dense than
water
• Reason for the
relatively high
b.p. of water
• Responsible for
the double helix
of the DNA
molecule
Hydrogen Bonds
2 lone
pairs
H
+
H
O
O
H
+
H
Nonpolar or Polar Molecules
• We now know how to determine if
the bond b/w atom and atom in a
compound is polar or nonpolar.
• But…what about the whole
molecule?
Nonpolar or Polar Molecules
• Draw the Lewis Structure.
• If the central atom has any unshared pairs,
the molecule is polar.
Nonpolar or Polar Molecules
• If there are no unshared pairs on the central atom,
look at the atoms around the central atom.
– If they are all the same, the molecule is nonpolar.
– If any one of them is different, the molecule is
polar.
• In a 2-atom molecule, if the bond between the 2
atoms is polar then the whole molecule is polar.
Nonpolar or Polar Molecules
H2O
CO2
HCl
HCN
Polar
Nonpolar
Polar
Polar
N2 Nonpolar
CH3Cl Polar