ib topic 4: bonding. pure carbon is covalently bonded in three of different forms (allotropes) 1....
TRANSCRIPT
Allotropes of Carbon and Intermolecular Forces
IB Topic 4: Bonding
Carbon allotropes pure carbon is covalently bonded in
three of different forms (allotropes)1. graphite2. diamond3. fullerenes
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Graphite possesses a layer structure the layers of carbon atoms are
arranged in an repeating fashion
Diamond more compact structure and dense
than graphite one of the hardest materials known
Fullerenes highly stable chemically most famous is the “buckeyball”
› discovers awarded Nobel Prize in 1996› over 1000 fullerene compounds have been made
composed of carbon atoms that form a hollow, cage-like structure› interesting feature of fullerenes is their ability to
enclose other atoms
Intermolecular Forces forces that occur between molecules much weaker than intramolecular (within
the molecule) forces› it takes 464 kJ/mol to break the H-O bonds within
a water molecule and only 19 kJ/mol to break the bonds between water molecules
the strength of the intermolecular forces determines the physical properties of the substance› melting, boiling, reacting, solubility, conductivity,
volatility this will be covered in next PowerPoint
van der Waals forces
van der Walls YouTube (:20) also also known as London Dispersion
Forces even nonpolar molecules have forces that
hold them together the distribution of electrons around an
individual atom, at a given instant in time, may not be perfectly symmetrical› this can produce a temporary, instantaneous
dipoles (polar molecule)› this can then induce a nearby molecule to be
polar and therefore a very weak attraction between the two molecules and so on, and so on…
Sticky secret. Tiny hairs on geckos' feet help maximize
contact with surfaces, allowing van der Waals forces to go to work.
Dipole-Dipole Forces attractive forces between the positive end
of one polar molecule and the negative end of another polar molecule
must be in close proximity for the dipole-dipole forces to be significant
stronger than van der Waal's forces
Hydrogen Bonding
YouTube Hydrogen Bonding (1:40) YouTube Hydrogen Bonding Video (:58) a specific type of dipole-dipole type
interactions stronger than other dipole-dipole and/or
dispersion forces the hydrogen in a molecule (e.g. H-F, H-
O or H-N) is bonded to a small, highly electronegative element (usually an F, O or N atom) on another molecule