3. structure bonding and properties Flashcards
what are giant covalent lattice’s (also knows as macromolecular structures)
huge network of covalently bonded atoms
why can carbon form a giant covalent lattice?
crbon can form 4 strong covalent bonds
what are different forms of the same element in the same state called?
e.g.
allotropes
carbon - diamond graphite and graphene
diamond
- each C atom is covalently bonded to
- what shape
- what structure
- 4 other carbon atoms
- tertrahedral shape
- crystal lattice structure
Diamond has lots of strong covalent bonds which gives it 5 certain properties
- high melting point
- extremely hard
- good thermal conductor (vibrations travel easily through it)
- can’t conduct electricity (localised bonds)
- wont dissolve in any solvent
other than carbon what other element can form a crystal lattice structure
Silicon
a silicon atom is able to form how many strong covalent bonds
4
why does graphite feel slippery / why is it used as a dry lubricant and in pencils?
weak forces between layers in graphite easily broken. sheets can slide over each other.
why can an electric current flow through graphite?
delocalised electrons are free to move along the sheets
why is graphite less dense than diamond?
layers are far apart compared to length of covalent bonds
the fact that graphite is less dense means it is used to make
strong lightweight sports equipment
why does graphite have a very high melting point
strong covalent bonds in the hexagon sheets
why is graphite insoluble in any solvent?
covalent bonds too strong to break
how many carbond atoms is each carbon covantly bonded to in graphite
3
what happens to the 4th outer electron of carbon in graphite
it is delocalised between the sheets of hexagons
how are the sheets of hexagons bonded together in graphite
london dispersion forces (weak)
what is graphene
1 layer of graphite
sheet of c atoms joined together is hexagons
1 atom thick - 2D
useful properties of graphene
why is graphene the best known conductor
delocalised electrons free to move along sheet. no layers = move quickly above an below sheet.
useful properties of graphene
why is graphene extremely strong
delocalised electrons strengthen the covalent bond between c atoms
3 useful properties of graphene
- extremely strong
- best known conductor
- transparent and incredibly light
graphene
properties of being light and transparent - potential use?
touch screens on smartphones
graphene
properties of high strength low mass and good electrical conductivity - potential use?
high speed electronics
aircraft technology
what structures do metal elements exist as
giant metallic lattice structures
giant metallic lattice structure
- electrons in outermost shell of metal atom delocalised. electrons free to move. leaves positively charged metal cation e.g. Na+, Mg2+, Al3+
- metal cations electrostatically attracted to delocalised negative electrons. form lattice of closely packed cations in sea of delocalised electrons - this is metallic bonding
what affects melting point of a metal
- number of delocalised electrons per atom. more delocalised electrons, stronger bonding, higher melting point.
- size of metal ion and lattice structure. smaller ionic radius delocalised electrons closer to nuclei.
why are metals malleable (can be hammered into sheets) and ductile (can be drawn into a wire)
no bonds holding specific ions together
metal ions can slide past each other when structure is pulled
why are metals good thermal conductors
delocalised electrons can pass kinetic energy to each other
why are metals good electrical conductors
delocalised electrons can move and carry a current
why are metals insoluble (except from liquid metals)
strength of metallic bonds
3 examples of simple molecular structures
O2
Cl2
P4
S8
why do simple molecular structures have low mpt & bpt
covalent bonds between atoms in molecule very strong
mpt & bpt depend on strength of london dispersion forces between molecues
london dispersion forces are weak and easily overcome = low mpt and bpt
why does S8 have higher mpt and bpt than Cl2 or P4
more atoms in a molecule
stronger london dispersion forcs
why do noble gases have very low mpt and bpt
exist as individual atoms (monatomic)
very weak LDF
period 2 and 3 for metals (Li, Na, Mg and Al) mpt & bpt increase across the period because
metallic bonds get stronger
ionic radius decreases
number of delocalised electrons increases
period 2 and 3
for element with giant covalent lattice structures (C and Si) mpt and bpt is very high because
a lot of energy needed to break the strong covalent bonds
period 2 and 3
for elements that form simple molecular structures low mpt and bpt because
weak intermolecular forces (LDF)
period 2 and 3 noble gases (neon and argon) have lowest mpt and bpt because
held together by weakest forces
ionic bonding
- examples
- mpt & bpt
- typical state
- does solid conduct electricity
- does liquid conduct electricity
- is is soluble in water
- NaCl. MgCl2.
- high.
- solid.
- no, ions held in place.
- yes, ions free to move.
- yes.
simple molecular (covalent)
- examples
- mpt & bpt
- typical state
- does solid conduct electricity
- does liquid conduct electricity
- is is soluble in water
- CO2. I2. H2O.
- low. have to overcome LDF or H bonds, not covalent bonds.
- sometimes solid. usually liquid or gas.
- no
- no.
- depends on how polarised the molecule is.
giant covalent lattice
- examples
- mpt & bpt
- typical state
- does solid conduct electricity
- does liquid conduct electricity
- is is soluble in water
- diamond. graphite. graphene.
- high.
- solid.
- no (except graphite and graphene) .
- will generally sublime.
- no.
metallic
- examples
- mpt & bpt
- typical state
- does solid conduct electricity
- does liquid conduct electricity
- is is soluble in water
- Fe. Mg. Al.
- high.
- solid.
- yes (delocalised electrons).
- yes (delocalsied electrons).
6 no.
