Metallic Bonding
Covalent Bonds can be polar
or non-polar
• Polar Covalent
– when electrons are shared
unevenly
– large difference in
electronegativities
•Nonpolar Covalent
Takes place in a
“SEA” OF MOBILE VALENCE ELECTRONS
Polarity
• Polar- uneven distribution
of charge in a bond.
• Dipole Moment - the
lopsided property of some
molecules with polar
bonds.
–when electrons are
shared evenly
–very small difference in
electronegativities
Electronegativity: “electron hogging”
Ionic Bonds: When e-neg’s are vastly different
Covalent Bonds: When e-neg values are close
…it is a gradational boundary.
We show partial charges on structure by using  (lowercase delta)
Percent Ionic Character
The more polar the molecule,
the more like an ionic bond its bonds are.
Physical Properties
often depend on bond type:
We will compare the
•
Melting Point
•
Solubility
•
Conductivity
•
Conductivity in Solution
of ionic and covalent compounds in a lab.
Make sure you consider your results!
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Ionic vs. Covalent
Ionic Solids are
network structures;
they have a crystal
lattice.
Covalent Solids are
molecular; they exist as
separate, discrete
molecules.
The formula of a covalent
compound describes a
molecule:
The formula of an ionic
compound describes
a “unit cell”
So what holds the molecules of
covalent compounds together?
Ionic
compounds
are held
together by
a crystal
lattice;
a network
of cations
and anions.
Intermolecular Forces:
• Hydrogen Bonds
• Van der Waals Forces
– London Dispersion Forces
– Dipole-Dipole Interactions
Hydrogen Bonding
Hydrogen bonds
The H atoms in water are a perfect example:
• Hydrogen is an exceptional element in that
when it forms a covalent bond, its one electron
is held to one side of the nucleus leaving the
other side relatively bare.
HThat bare side of Hydrogen exposes a
positive nucleus, which can attract nearby
negative charges, forming a “hydrogen bond”
The exposed
nuclei of the H
atoms
attract the
“negative side”
of adjacent
water
molecules.
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