Intermolecular Forces of Attraction
• Ch 12 was all about gases… particles that don’t attract each other.
Intermolecular Forces of Attraction
• Ch 13 is about liquids and solids… where the attraction between particles allows the formation of solids and liquids.
Intermolecular Forces of Attraction
• These attractions are called “intermolcular
forces of attractions” or IMF’s for short.
• Intermolcular forces vs intramolecular forces
Four Solids – Overview
• Molecular Solids (particles with IMF’s)
• Metals (metallic bonding)
• Ionic Solids (ionic bonding)
• Covalent Network Solids (covalent bonding)
Molecular Solid Examples • H2O
• CO2
• CH4
• NH3
• NO2
• CO
• C2H6
• C2H5OH
• C6H12O6
• The alkanes, alkenes, etc.
• The diatomic molecules
• The noble gases
Metals
• A lattice of positive ions in a “sea of electrons”
• Metal atoms have low electronegativity
Metal Examples
• Pb
• Ag
• Au
• Cu
• Zn
• Fe
• Brass (Cu + Zn)
• Bronze (Cu + Sn)
• Stainless Steel (Fe/Cr/C)
Ionic Solid Examples
• NaCl
• KCl
• KI
• FeCl3
• CaCO3
• CaCl2
• MgSO4
• Fe2O3
• AgNO3
• + ion & - ion
Covalent Network Solid Examples
• C(diamond)
• C(graphite)
• SiO2 (quartz, sand, glass)
• SiC
• Si
• WC
• BN
Properties of
Metals
Metals are good
conductors of heat and
electricity.
They are shiny and
lustrous.
Metals can be pounded
into thin sheets
(malleable) and drawn
into wires (ductile).
Metals do not hold onto
their valence electrons
very well. They have low
electronegativity.
Intermolecular Forces (IMFs)
• Each intermolecular force involves + and –
attractions.
• The list from weakest to strongest is:
– London Dispersion Forces
– Dipole-dipole interactions
– Hydrogen bonding
– Ion-Ion Interactions
Ion-Ion Interaction
• + ion attracts a – ion (opposites attract)
• Lattice energy is a measure of the
strength of this interaction
• NaCl(s) + energy Na+(g) + Cl-(g)
Dipole-Dipole Interaction
• Same idea as ion-ion interaction, but not
as strong because the charges are only
“partial charges”.
• Polar molecules have this kind of IMF.
Hydrogen Bonding
• This is a special case of dipole-dipole
interaction (about 10x stronger).
• H-O, H-F, H-N
– Atoms are small and electronegative
– Very polar bond leads to stronger IMF
London Dispersion Forces
• Every atom attracts every other atom with
this force. (H-bonding & LDF, Dipole & LDF)
• +/- attraction again but the polarity is only
temporary.
• LDF is stronger with a “more polarizable
electron cloud”. (use these words in FRQ)
– More electrons
– Larger atoms or longer molecules