Properties of Ionic and Covalent
Compounds
Intermolecular Forces
Physical Properties & Bond Types
• Physical properties of substances are affected
by the attractive forces between particles
– Greater attraction between the molecules →
more energy is required to overcome the
attractive forces between molecules
• Increased melting point or boiling point
• Solubility depends on “like dissolves like.”
Structure of an Ionic Solid
• Ionic Compounds form
a three-dimensional
network called a crystal
(or crystal lattice)
• Each ion is attracted to
multiple ions of the
opposite charge
Forces Between Particles
Interionic Forces
• Due to the attraction of
oppositely charged ions
• There is a greater
attraction between ions
of greater charge
• Strongest forces
between particles
found in ionic
compounds
General Properties of Ionic
Compounds
• High melting/boiling points
– Solids at room temperature
• Many are soluble in water
– Ions separate when dissolved in water
• Liquids & Solutions → Good Conductors
– Ions are separated – any substance that has separate
charges allow for conduction of electricity
• Solids → Poor conductors
– No separation of ions
General Properties of Covalent
Compounds
• Lower Melting Points than ionic compounds
– Intermolecular Forces aren’t as strong as
interionic forces
• Cannot conduct electricity as solid, liquid, or
when dissolved
– molecules will not separate into ions
• Will dissolve in liquids with similar molecular
polarity
– “Like dissolves like”
Nonpolar Covalent Bonds
• Some atoms have similar attraction for
electrons, so the shared pair(s) will be evenly
distributed between each atom
– There are no “positive” or “negative” sides
• This is referred to as a nonpolar covalent
bond
• Because there is no separation of charge
within the molecule, they have little or no
attraction for one another
General Properties of NonPolar
Covalent Compounds
• Really low melting points and boiling points
– Many are gases at room temperature
• Cannot conduct electricity as solid, liquid, or
when dissolved
– molecules will not separate into ions
• Will dissolve in liquids with similar molecular
polarity
– “Like dissolves like”
Polar Covalent Bonds
• Some atoms have a greater attraction for
electrons than other atoms
– Due to greater electronegativity
• When these atoms form a covalent bond, the
electrons will not be shared equally
• This is referred to as a polar covalent bond
Attraction Between Polar Compounds
Hydrogen is
“positive”
The negative part
of one water
molecule is
attracted to the
positive part of
another water
molecule
Hydrogen is
“positive”
Oxygen is
“negative”
Intermolecular Forces
Dipole Forces
• Polar molecules are
attracted to each other
via the “negative” end of
one molecule being
attracted to the “positive”
end of another molecule
– Not as strong as ionic
forces, but stronger than
the very weak forces that
(barely) exist between
nonpolar molecules
Differences Between Polar and
Nonpolar Covalent Compounds
• Polar molecules will attract each other SLIGHTLY
– Nonpolar molecules have no attraction for each other
• Polar Compounds will have slightly higher melting
points, but not as high as ionic compounds
• Still no ability to conduct charges
• Polar compounds will dissolve in other polar
compounds, but not in nonpolar compounds
Boiling Point Comparison
Forces Between Particles
Hydrogen Bonding
• Strongest of the intermolecular forces
– Attraction between molecules, not ions
• Hydrogen bonding arises where hydrogen
atoms are bonded to highly electronegative
elements such as F, O, and N
Forces Between Particles
Hydrogen Bonding
General Properties of Covalent
Compounds that Exhibit Hydrogen
Bonding
• Lower Melting Points than ionic compounds, but
higher than nonpolar or polar covalent compounds
– Intermolecular Forces aren’t as strong as interionic forces,
but Hydrogen bonding is stronger than other
intermolecular forces
• Cannot conduct electricity as solid, liquid, or when
dissolved
– Still no ions
• Will dissolve in liquids with similar molecular polarity
– “Like dissolves like”