S2.2 IMF's & cov. networks Flashcards
Allotropes
atoms of the same element with different chemical and physical properties
covalent network
goant covalent substances
Diamond
- C to 4C
- tetrahedral arrangement (109.5)
- no delocalised electrons (not conductor)
- strong covalent bonds
- high mp/bp
- very hard
Graphene
- one layer graphite (2D)
- conductor
- synthetic & strong
- hexagonal strcuture
Graphite
- C bonded to 3C => hexagonal
- delocalised e
- conducts electricity
- layers held by LDF
- lubricant
Silicon
- S bonded to 4S
- tetrahedral (109.5)
- poor conductor
- very high mp/bp
Silicon dioxide
- sillica/quartz
- poor conductor
- high mp/bp
- tetrahedral (109.5)
Fullerenes
molecules which contain 60-70 carbons
example: Buckmister = 5 & 6 membered carbon rings
Fullerenes
covalent nanotubes
graphene rolled to form tube
=> delocalised electrons = conductors
used in medical industry = binds to specific target molecules
van der waals forces
weak intermolecular forces between atoms and molecules
london dispersion forces
- weakest
- occurs in all atoms and molecules
temporary instantaneous dipole formed due to the rapid and random motion of electrons
=> electrostatic attraction between temporary induced dipoles
Permanent dipole
- stronger than LDF
intermolecular force between two polar molecules that have a permanent dipole
=> negative attracted to positive
Hydrogen bonding
- very strong permanent dipole
- other atom MUST have lone pair
Intermolecular attraction between two molecules which both contain a hydrogen bonded to a highly EN element such as O2, F or N
induced dipole
- weaker than perm. dipole
- temporary
Dipole of one atom/molecule induces a dipole of a neighboring atom/molecule
=> particles become attracted to eachother
Immiscible
liquids that do not mix together
TLC
thin layer chromatography
utilises thin layer of inert substance (sillica) as the stationary phase
IMF & Melting points
- In non polar = LDF have affect
- LDF increase as mass increases
- more electrons = higher b.p/m.p
Polar molecules B.P
higher mp/bp. = more energy required to overcome permanent dipole
IMF - Alkane branched vs straight b.p
Branched
* can’t pack closer
* less points of contact
* weaker LDF
* lower b.p/m.p
Straight
* can pack closer
* more points of contact
* stronger LDF
* higher m.p& b.p
Melting Point - H bond
very high m.p
IMF - viscosity
the stronger the van-der-waals forces = the more viscous the liquid
