Please enable JavaScript.
Coggle requires JavaScript to display documents.
SOLID STATE, DEFECTS - Coggle Diagram
SOLID STATE
CRYSTALINE
Ionic crystals
- constituent particles are charged ions
- particles are held by electrostatic force of attraction between oppositely charged ions
- hard,brittle and high melting point
- nonconductors in solid state but good conductors when melted or dissolve in water
(eg NaCl,,K2O4,KCl)
Covalent network crystals
- constituent particles are atoms
- atoms are linked by continuous system of covalent bonds resulting in a rigid 3D network that forms a giat molecule.entire crystal is a single molecule
- very hard,incompressible,high bp and mp
- e-are localised so poor conductors of heat and electricity
(eg.diamond,quartz,boron nitride
Molecular crystals
- constituent particles are molecules (or unbonded single atoms)of the same substance
- bonds in the molecules are covalent,molecules are held together by diff forces;weak dipole dipole interaction in polar molecules(solid HCl,H2O,SO2)which possess permanent dipole moment,very weak dispersion or london forces in non-polar molecules(solid ch3,H2),intermolecular H-bonds in solids such as H2O(ice),NH3,HF
- soft and low mp
- poor electricla conductors but good insulators
Metallic crystals
- formed by atoms of the same metallic element held together by metallic bond
- in solid metals valence e- are delocalized over entire crystal leaving behind +vely charge metal ions
- hence they are described as an array od positive ions immersed in a sea of mobile e-,the attractive interaction betn cations and mobile e-=metallic bond
- malleable,ductile,good conductor heat and electricity
(Na,K,Ca)
-
CRYSTAL STRUCTUE
UNIT CELL
primitive or simple unit cell
- constituent particles are present at corners only
body centred unit cell
- 1 constituent particle is present at the centre of its body in addition to corner particles
face centered unit cell
- particles at centre of each face in addition to corners
base centred unit cell
- particle at centre of any 2 opp faces in addition to corners
7 CRYSTAL SYSTEMS;
- cubic,tetragonal,orthorhombic,rhombohedral,monoclinic,triclinic and hexagonal
- 14 Bravias lattices
SC
- particle at each of 8 corners of cube
BCC
- particles at 8 corners as well as one at centre of cube
FCC
- particles at 6 faces as well as on 8 corners
NO.OF PARTICLES IN CUBIC UNIT CELL
- SC=1 particle per unit cell
- BCC=2 particles per unit cell
- FCC=4 particles per unit cell
-
-
-
DEFECTS
Point defect
- irregularities produced in the arrangement of basis at lattice point
stoichiometric point defect
- stoichiometry remains unchanged i.e ratio of no. of atoms or cations and anions of compound remains same as chemical formula
vacany defect
- during crystalisation of solid,a particle is missing from its regular site in crystal lattice
- missing particle creates vacancy in lattice structure
- it can be developed due to heating of substance
- due to absence mass of substance decreases,vol unchanged but density decreases
self interstital defect on elemental solid
- when some particles of crystalline elemental solid occupy interstitial sites in crystal structure
- it occurs in 2 ways;1stly an extra particles occupies an empty interstitial space,this increases total mass without increasing vol so density increases
- 2ndly in elemental solid a particle gets shifted from its original lattice point and occupies an interstitial space,it preserves density
schottky defect
- in ionic solid equal no. of cations and anions are missing from their regular positions in crystal lattice creating vacancies
- conditions;
1.high degree of ionic character
2.high CN no. of anion
3.small diff betn size of cation and anion, ratio of cation to anion is not far below unity
- consequences;
1.mass decreases and density decreases
2.electrical neutrality of the compound is preserves
(NaCl,AgBr,KCl)
frenkel defect
- an ion of an ionic compound is missing from its regular lattice site and occupies interstitial sites
- since cations are smaller they commonly occupy interstitial site
- conditions;
1.occur in ionic compounds with larger diff between sizes of cation and anion
2.ions should have low CN
- consequences;
density and chemical prop remain unchanged
- crystal remains electrically neutral
(ZnS,AgCl,AgI)
Impurity defect
- when foreign atoms are present in the crystal
substitutional impurity defect
- foreign atoms are found at the lattice sites in place of host atoms
- regular atoms are displaced from their lattice sites by impurity atom
- eg.solid soln of metal;brass=cu and zn alloy,in brass host cu atoms are replaced by impurity of zn atoms,zn atoms occupy regular sites of cu atom
- vacancy through aliovalent ions;vacancies are created by addition of impurities of aliovalent ions to an ionic solid
interstitial impurity defect
- impurity atom occupy interstitial spaces of lattice structure
nonstoichiometric defects
- stoichiometry of the compound is changed i.e ratio of no. of atoms of one kind to that of other kind or ratio of cations to anions becomes diff from that indicated by chem formula
metal deficiency defect
- possible only in compounds of metaksthat show variavle O.S
- +ve metal ions are missing from their original lattice sites,the exta-ve charge is balanced by the presence of cation of the same metal wit higher O.S than missing cation
metal excess defect
a neutral atom or an extra +ve ion occupies interstitial
- it occurs in 2ways in ZnO;
in 1st in ZnO lattice one neutral Zn atom is present in the interstitial space
in 2nd when ZnO is heated it decomposes ,excess Zn+2 ions are trapped in interstitial spaces and e- also diffuse in the crystal to occupy interstitial sites
by anion vacancies(color or F-centre)
- this defect imparts color to colourless crystal
- eg.when NaCl is heated in atmosphere of Na vapour,Na atoms are deposited on crystal surface,Cl- ions diffuse to the crystal surface creating vacancies at their regular sites,these Cl- ions combine with Na ions on surface to form NaCl by releasing e- from Na atom,there released e- diffuse into the crystal to occupy vacant sites of anion.
- the anion vacant sites occupied by e- are F-centres or colour centres.NaCl shows yellow colour due to F-centre,crystal of NaCl has excess Na