topic 1🅱️ Flashcards
solid
state of matter
particles are arranged in a way that makes their shape + volume stable
what is solid state chem
it’s about making/ preparing solids
structure of solids
properties of solids
ionic bonding
regular arrays of positively and negatively charged ions
electrostatic forces of interaction
covalent bonding
atoms in the compound share electrons in order to obtain an octet figuration.
lewis model + MO bonding theory
why do we use the terms ionic and covalent character
bc bonding is a spectrum.
it’s never either the 2 extremes but a combo of both
types of solid: molecular solid
- solid made up of molecules
- bonds are covalent (strong)
- intermolecular bonds are weaker (H, DD, VDW
- soft materials
- low melting points (only the intermolecular need to be broken to change state)
in molecular solids,, what interaction needs to be broken in order for them to change state
intermolecular interaction!!!
HYDROGEN, DIPOLE DIPOLE,, VDW
the covalent bonding (intra) doesn’t need to be broken
types of molecular solids
Iodine
I2 = covalently bonded
I2 —- I2 (van der waals interactions)
describe iodine solid
covalent between I and I
VDW between I2
VDW = strong enough for iodine to be solid at room temp. (lots of e-)
- solid sublimes easily into vapour
- low 113.7* melting point
sublimation // sublimes meaning
going from solid to gas // vapour
doesn’t go through the liquid phase // state
another example for a molecular solid
sulfur
describe sulfur
- solid in ambient conditions
- contains S8 ring molecules
- covalent S and S
- VDW // dispersion between S8
- soft, bright, yellow at room temp
- low mp of 115.2*
- sublimes easily
what are covalent network solids
- covalently bonded atoms that form a continuous infinite network
what can form covalent network solids
elements (C)
compounds (SiO2)
describe covalent network solids
high melting + boiling points
hard
brittle (covalent bonds must be broken to change state)
examples of covalent network solids
graphite
diamond
quartz
a-crietobalite
further examples of covalent network solids
carbon!!
it has many allotropes
what’s an allotrope
different solid stage structures of the same element
describe C,, CNS : graphite
- layers of sp2 hybrid C
- high mp (covalent within layers)
- pencils + lubricants (VDW between layers - slips)
- conductive ( delocalised e- between layers)
CNS: C : diamond
- sp3 hybrids (single bonds)
- 4 covalent bonds each (hard solid + high mp)
- no delocalised e- : not conductive
CNS: C : graphene
single sheet of graphite
similar properties to graphite (high mp, conductive )
very strong
very light
CNS : C : fullerenes
nanotubes
rolled sheet of graphite
strong, light, conductive
buckyballs: lower mp ( VDW between spheres)
difference between fullerenes and graphene
graphene is a flat sheet of graphite
fullerene is a rolled sheet of graphite
fullerenes can also include nanotubes or buckyballs
CNS: SiO2 (silicone dioxide)
- covalent bonds between Si and O
- many diff know structures (polymorphs)
what is a polymorph
different solid stage structures of the same compound
what are the 2 polymorphs of SiO2
quartz
a-cristobalite
describe quartz : CNS (SiO2)
most common polymorph
natural mineral
most common mineral on the earth
describe a-cristobalite : CNS: SiO2
common polymorph of SiO2
also has its own polymorphs at high and low temperatures
describe a metallic solid
- cations in a sea of delocalised electrons
- interactions between cations and e- = strong metallic bonding
- hard solids + mp + bp due to strong metallic bonding
- only valence e- contribute to the bonding + are delocalised
- conductive in solid + molten form
ionic solid type of solid
- cations and anions
- electrostatic forces between oppositely charged ions holds them together
- high melting + bp
- hard and brittle (strong ionic bonds)
- conductive when molten or dissolved in aq solution
what elements are more likely to form ionic compounds
those that are more easily ionised
more readily ionised
aka lower ionisation energies.
example of an ionic solid
NaCl
sodium chloride
Na+ and Cl-
what is a crystal
a crystalline solid
what is a crystal or a crystalline solid
solid consisting of a regular and repeating array of atoms, molecules, ions.
extend in 3 dimensions to give an ordered structure
what type of symmetry does a crystal have
translational symmetry
what is translational symmetry
a movement, shift or slide in a specific direction by a specific distance without rotation or reflection
what is a unit cell in a crystal
the smallest repeating unit of a crystal
how many parameters is a unit cell described with
6
what 6 parameters are used to describe a unit cell
3 vector lengths : a b c
3 angles : a B y
what the relationship between the crystal parameters in a cubic unit cell
a = b = c
a = B = y = 90*
how is a full crystal structure generated
when the unit cell is translated in 3 directions
when translational symmetry occurs me
what are the 4 other basic crystal symmetry
- mirror symmetry
- inversion symmetry
- rotational symmetry
- rotary inversion symmetry
combo of what allows us to build up an entire crystal structure
combo of all the symmetries
- mirror
- rotation
- translation
- inversion
- rotary inversion
1 fold in rotational symmetry
360*
2 fold in rotational symmetry
180
4 fold in rotatory symmetry
90
how can we determine the crystal structure // the structure of crystalline solids
analytical technique
- x ray crystallography
how does the analytical technique of x ray crystallography determine the solid structure of crystalline solids
- x ray beam is shone on crystal
- diffraction occurs as x ray beam wavelength is similar to the order of gaps between atoms
- detector is used to identify the diffraction pattern which is mathematically related to the structure of a crystal
close packing + atoms :: what will always be present
small gaps will always be present no matter how tightly u pack the atoms together
what is the most efficient way for atoms to pack together to minimise the amount of space between them
close packing
it minimises the amount of space between them
close packing : A
looks like a bunch of flower heads
each atom is in contact with 6 atom neighbours
one close packed layer
close packing AB
spheres in layer 2 sit between the first layers gaps
2 close packed layers
3 close packed sphere layers
2 options:
- ABA : spheres in 3 sits directly above layer 1 ( hexagonal close packing) flower up front,, gaps go all the way through
- ABC : spheres in layer 3 sit directly above layer one gaps (cubic close packing) (no spheres are directly above each other,, all layers are different,, no straight through gaps)
what repeats does cubic close packing (ccp) aka the triangle top shape have
ABCABCABCABCABCABCABC
cubic for c!! each layer is different,, no atoms are directly above other atoms,, no straight through gaps.
what repeat does hexagonal close packing have (aka the flower on top)
ABABABABABABABABABAB
most common close packing arrangements
CCP
HCP
in how many directions must a unit cell be translated in order to general the full crystal structure
must be translated into three directions
what is the ‘cubic’ is ccp referring to
the cubic symmetry of its structure
- a=b= c
- a = B = y = 90*
how else can the ccp unit cell be called
face centred cubic (fcc)
what are other important cubic cell units called
body centred cubic (bcc)
primitive cubic (pc)
are bcc or pc close packed
nope!!
neither of them are close packed
what is face centred cubic (fcc)
atoms are on all cube vertices and in the centre of the faces
what is body centred cubic (bcc)
atoms are on all vertices of the cube
1 atom in the centre of the cube
what is primitive cubic
atoms are seen on all vertices of the cube only
what does the hexagonal in hcp stand for
the hexagonal symmetry of the structure
what conditions are seen in the unit cell or a hexagonal structure
- vectors: a=b NOT c
- angles: y=120
what elements can adopt the CCP HCP BCC
metallic elements!!
phase transitions can occur between different structures under ambient temp and pressure
what structure does metallic Cu^0 adopt
CCP
FCC
what structure does metallic Ti ^0 adopt
hcp
what structure does metallic Iron m,, Fe^0 adopt
bcc
make it known!! ccp is
cubic close packing
also known as face centred cubic
ccp is
cubic close packing
ccp can also be called
fcc
what is fcc
face centred cubic
also known as cubic close packing
what is hexagonal close packing
ABABABAB
ccp is called,,, and how many different ones are there
cubic close packing
also known as face centred cubic
- body centred cubic
- primitive cubic
which structures are closely packed
cubic close packing ABC
(face centred cubic)
hexagonal close packing ABAB
which structures arent closely packed
body centred cubic
primitive cubic
which holes can u see all the way through
hexagonal closed packing
ababababa
H exagonal for Holes
3 above and 3 below
which holes can u not see all the way through
cubic close packing
3 above
1 below
C ubic for ABC
coordination number of an atom in hcp
12
3 above
6
3 above
coordination number of atoms in a ccp
12
3 above
6
3 above
bcc coordination number
8
primitive coordination number
6
primitive cubic can also be called what
simple cubic
atoms on corners only
what is packing efficacy
percentage of the structure that is filled by atoms
for a bcc: packing efficacy
u need to put a bit more effort in.
first find x by doing
L2 + L2 = X2
then do X2 + L2 = 4r2
then do the whole atom volume thing
and do L3 to find the volume
number of atoms in ccp
4
number of atoms in hcp
2
number of atoms in bcc
2
number of atoms in primitive cubic // simple cubic
1
packing effficacy of hcp and ccp
74%
packing efficacy of bcc
68%
packing efficacy of primitive
52.4%
close packed structures intersitital sites
tetrahedral
octahedral
how many octahedral sites per atom
1
site is bonded to 6 atoms
3 below
3 above
can see through
how many tetrahdral sites per atom
2
site is bonded to 4 atoms
3 above
1 below
cant see through
length of ccp/fcc
8 1/2 r
cube this to get volume
