lecture 2 Flashcards
what is orbital hybridisation
combining atomic orbitals to generate combinations of them
sp hybrid shape and angle
triple bond
linear
180*
sp2 hybrid shape and angle
double bond
trigonal planar
120
sp3 hybrid shape and angle
single bond
tetrahedral
109.5
if smt is in group 5,, how many bonds are needed for it to be sp3 hybridised
group 5 so 5 e-
needs 5 bonds in order to be sp3 hybridised
when do we see single connectivity
when we form discrete molecular systems
when we have units
which only contain a single free connecting unit.
aka a fg that will react with 1 other molecule.
example of single connectivity
lewis acid/base adducts
NMe3 + BPh3
N: attacking the B p orbital
——————————————————
condensation reaction between 2 moelcules only!! when both have OH groups,, and water is removed and theyre bonded through the ‘o’.
also called a condensation reaction as water is removed.
what is 2 connecting units
when the repeat unit has a connectivity of 2,,, the units can link in a consecutive way to form rings or 1D polymers
this is different to single connectivity as both sides of the molecule has a connective unit to it.
what do 2 connectivity units give rise to
either to rings or 1D polymers
1 connecting unit
the molecule only has 1 connecting point // connecting group
2 connecting units
when the molecules have 2 connecting pointssss // connecting groups and can form 1D polymers or ring systemssss
condensation reactions are a possibility
how do we draw a polymer
we draw the repeating unit with extended end lines,, with a bracket going through it and an ‘n’ at the bottom of the bracket.
-(- hello -)-
can u react a 1 connecting unit with a 2 connecting unit
yesss!!
we use this in order to cap polymers as a certain length // certain number of repeats
we can use the 1 connectivity at the ends as by connecting to the chain,, they have no more connecting sites.
polymers that have been capped can be called
discrete chains
how many bonds does a single connectivity unit make
1
how many bonds does a double conectivity unit make
it makes 2 bonds
which can either form a ring or 1D polymer
what can units with 3 connectivities give ussss
planar sheets ✈️✈️✈️
or closed cagessss🦁🦁🦁
what geometries can units with 3 connections haveee
can be trigonal planar //sp2
or tetrahedral with an unreactive site.
final structure can be determined byyyyy
coordination geometries ( eg planar,, tetrahedral etccc)
whats special about the 4 and 6 connectivity units
their geometries dictate their final lattice geometry
4 / 6 connectivity units:
square planar connectivity units give whattt
2D sheets
4/6 connectivity units:
tetrahedra connectivity givesss
3D network like graphite
6 connections normally giveeeee
3D structures
when building main group compounds what must we consider
energetics!!
the stability of the element form or the molecular forms
we normally look at 1D chains and rings
we must also consider
thermodynamics
what do we mean when we say thermodynamics
entropy and enthalpy
when is delta G favoured
when its negative
when its smaller than 0
when is delta G not favoured
when its larger than 0.
equation for gibbs
delta G = delta H - T delta S
when we say covalent bonds,, what do we mean
sigma or pi bonds
iss CC or PbPb bonds stronger
CC is stronger
bc it has a smaller atomic radius
which means a greater degree of orbital overlap
which means a stronger bond
the bond is lower in energy
the more stable smt isss
the lower energy it hasss
the lower enthalpy it hasss
as it was storing less to begin with <3
