2.3 metallic model Flashcards
giant covalent structures
no limit to size, have a ration of atoms though
in this case the intramolcular forces or strong attractive force extends throughout the whole giant molecule, this greatly affects phyiscal and chemical properties of material
examples of giant covalent
diamond
graphite
fullerene
graphene
silicon
silicon dioxide
allotropes
different physical forms of the same element, all elements are made up uniquely of their own atoms and therefore any physical difference must be a consequence of how the atoms are joined together, their arrangement within the bulk structure
many elements exhibit allotropy as there are often various ways in which the atoms can be linked together into molecules and also different ways in which the molecules can be arranged to make larger structures
allotropes of carbon explain
the atoms form either giant macromolecular strucutes in which all of the atoms in the bulk structure are joined together by covalent bonds making giant molecules or smaller moleculers in which there are only discrete molecules made up of 60 carbons in a structure
diamond
carbon can form 4 covalent bonds this makes a giant macromolecular array (lattice), as each carbon has 4 single bonds it is sp3 Hybridised and has tetrahedral bond angles of 109.5
tetrahedral arrangement
diamod properties and explanation
hard- many covalent bonds holding strucutre together, preventing change in shape
brittle- all bonds are directional and stress will tend to break the structure if sufficiently high covalent bonds are broked but do not reform themselves
insulator- all of the valence electrons are used in bonding there are no electrons free to move through the structure
insoluble- there are only weak london dispersion forces betweent eh carbon atoms and water molecules, wheras the carbon atoms are bonde very tightly to one another
very high melting point- many strong covalent bonds holding the strucutre together it recquires massive amounts of energy to pull it apart
graphite
again the arbon atoms are bonded together to make giant structure but in this case all of the carbons are bonded to only 3 others. This creates a giant 2d layered arrangement of carbon atoms and each layer is only weakly linked to the next layer by london disperion forces the elctron that is not bound to another is free to move around, this is why it conducts electricity
they are sp2 HYBRIDIZED, THIS RESULTS IN PLANAR STRUCTURES THERE ARE GIANT 2D LaYERS OF CARBON atoms and each layer is only weakly linked to the next layer by london dispersion forces
properties of graphite and explanation
soft and slippery- many strong covalent bonds holding the strucutre together but only in 2d. The layers can easily slide over each other it can be used in pencils and lubricant powder
brittle- all bonds are directional and stress will tend to break structure if sufficently high graphite ords used in electrolysis will snap if dropped
insoluble in water- there are only weak london dispersion forces between carbon atoms and water molecules whereas the carbon atoms are bonded tightly to one another
very highm.p-many strong covalent bonds holidng the strucutre together, it recquires massive amounts of energy to oull it apart
fullerene
not giant covalent
man made
these are small moleucles of carbon in which the giant structure is closed over into spheres of atoms
the bonding has delocolised pi molecular orbitals exending throughout the structure and the carbon atoms are a mixture of SP2 and SP3 hybridised systems, they are non conducters as the individual molecules ar eonly held to each other by weak london dispersion forces as the molecule is totally symmetrical
hybridizarion of carbon atoms is somewhere between that of SP2 and sp3
PHYSICAL PROPERTIES AND EXPLANATION fullerene
soft and slipery- few covalent bonds holding the molecules together but only weak vander waals forces between molecules
brittle- soft weak crystals typical of covalent substances
electrical insulator- no movmenet of elctrons available from on molecule to the next, exception could be the formation of nano tbes that are capable of conducting electrcitiy along their lengths
insoluble in water- there are only very weak van der waals attractions between carbon atoms and the water molecuels wheras the carbon atoms are bonded very tightly to one another in the molecules
low melting points- typical of covalent crystals where only van der waals interactions have to be broken when melting
graphene
thinnest and strongest material
2d crystak
is a covalent netqork solid, consists of single planar sheet of carbon arrange hexagonally, only one atom thick
each carbon atom is covalently bonded to another 3, carbon atoms densly pakced in a honeycomb crystalline lattice, but lattice is planar
properties of graphene and explanation
excellent thermal and electrical conductor
excellent lubricnat
silicon
forms 4 covalent bonds with 4 silcon atoms, ina tetrahedral arrangement
used in microcircuitry
silicon properties and explanation
semiconducter when doped with other impuraties eg. boron,
silicon crystals are blue/ grey
length of silicon silicon bond is much longer than carbon carbon bond, this means that the bond enthalpy is lower than fro carbon making bon dweaker and more reactive
silicon dioxide
giant covalent structure, 2 oxygens for every silicon so the moleculer formula is SiO2
lattice is much more ranom and dissorded than diamon
each silicon is bonded to four oxygens, each oxygen is onded to 2 silicons
properties of silicon dioxide and why
has similiar properties to diamond, however because lattice is more dissordered its melting point and strength and hardness are much less than diamond
giant ionic structures
ionic compounds ar emade up of positive and negative ions the ions arrange themselves in a giant ionic lattice where the positive ions are surrounded with negative and vice versa
alternating positive and negative ions arranging into a 3d giant ionic lattice, ions are held together in altice by ionic bond electrostatic force of attraction between positive and negative ions
solubility and ionic solids
if the electrostatic forcs are not too strong then ionic solids will dissolve in water to form solutions. The polar nature of the water molecules interacts with the positive and negative ions to break up the ionic lattice. This simple dissolving interaction with water is called hydration
the polar water molecules surround the ions and free them into solution
ionic compounds properties and explanations
Hard- many strong ionic bonds holding the structure together i 3d
brittle- the ionic bond is directionla if the ions slide over each other like charges will come together and repel causing the structure to fracture and break
insulator as solid- No free electrons so no current can flow in the structure. The ions are fixed in place in the ionic lattice
conductor in soludtions or molten- when molten or in solution the ions can move around freely allowing a charge to be carried
high m.p- many strong ionic bonds holding the structure together it recquires large amounts of eneergy to pull it apart
soluble in water- water has slight positive and negative charge so it can interact with the ions in the lattice , breaking up the structure and hydrating the ions
metallic bonding
the force of attraction between the positive metal ions and the sea of mobile negativ electrons
what can the properties of metals be explained due to
the ability of the metal atoms to lose their outer electrons which then become delocolised and free to move throughout the entire metal
unlike ionic bonding the metalic bond is non-directional and so distorting the atoms does not cause repulsion
electrical conductivity- metals
the negative delocolised electrons can be induced to flow through the bulk of the metal as a current when an external postential difference is applied
sea of mobile negative electrongs flow throguh metal
malleability and ductility-metals
if an external force is applied the metal ions can slide past each other without disruption of the electrostatic force of attraction between the sea of electrons and the metal ions, this mkaes metals ductile and malleable
force applied to lattice, metal ions sldie past each other and can be drawn into wires
high thermal conductivity- metals
the free moving electrons allow for high thermal conductivity and the electrons can carry the heat energy rather than it being transferred slowly through the atoms vibrating
state and explain trend in melting point in group 1
as you go down group 1 decrease m.p, nucleus in ion gets further away from the electrons as ionic radii is greater, meaning weaker electrostatic force of attraction thus weaker ionic bond
explain why magnesium is a better conducter of electricity than sodium
magnesium has more delocolised electrons its 2+ rather than sodium which is +
explian why aluminium has a higher metling point than sodium
aluminium has more delocolised electrons thus bigger attraction between delocolised electrons and sea of electrons and positive ions, greater metallic bond
Al is 3+ charged hence stronger electrostatic force of attraction between nucleus and delocolised electrons than sodium which is +
explain why metals conduct electricity in the solid state wheras ionic compiunds will conduct electricity only when molten or dissolved in water
metals when solid have delocolised electrons carrying charge
while ionic compounds when solid have no free ions, as they are held by ionic bond , its a fixed lattice when liquid these bonds are broken and ions are free to move
continuum of types of bonding
its a continuum between the three types of bonding models and that real materials often display a mixture of properties derived from all three models of bonding, this is shown in bonding triangles
what will determine where a material lies within the bonding triangle
electronegativity difference between different atoms in the structure and the avergae electronegativity of all atoms within the structure
zero- very low electronegativity differnece
the bonds are non polar because the material is an element or compiund with atoms that are very similar electronegativity the material has no polar or ionic character
eg. low avergae electronegativity= metal
medium to high average electronegativity= covalent
medium electronegativity differnece
increasing ionic character or molecules are polar
eg low avergae electronegativity= ionic
medium to high averga electronegativity= polar covalent
high electronegativity difference
substane is ionic
what are alloys
mixtures of metals with other elements can be metals or non metals
alloys of iron are referred to as
steels
most commony used is mild steel, allow with approvimately 0.5% carbon mixed into iron
why are alloys more useful than pure metals
can inhance properties of the pure metal, eg. may have greater corrosion resistance have differnet colours, or greater strength and the hardness than the pure metal alone
if an alloy is created atoms and impurity atoms have differnet sizes and this can prevent the layers from sliding past each other so easily making the alloy harder than the pure metal
alloy what happens when impurity element is another metal
then it also donates electrons to delocolised sea of electrons to leave a positive cation in the lattice, the impurity metal also contributes to the metallic bonding of the strucutre and the alloy malleability and ductility is not compromised compared to the pur metal , non directional bonding is maintained
carbon in iron (mild steel)
makes the iron harder, but carbon atoms are smaller and thus disrupt te metallic lattice, prevent layer of lattice from liding past each other. If content of carbon is too high then all malleability properties are lost and the steel is brittle
carbon does nto cotnribute to metallic bonding of lattice, if carbon content is too high non directinal bonding decreases.
brass composition and uses
copper and zinc
-resistant to corrosion
-musical instruments, gears, hinges
bronze
copper + tin
-hard material, low m.p
-used weapons and tools
solder
tin + lead
-low m.p
-connecting electricial wires
nickel steel
iron and nickel
-strong corrosion resistance and heat resistant
-crytogenic storage, chemical plants, gas turbines
stainless steel
steel + cr +ni
-resistant to corrosion, doesnt rust easily
-surface that need to be cleaned frequently
manganese steel
mn + c + cr
high impact resistance, corrosion reistant, work hardenning
industrial applications eg. mining equipment
