Solids are the substances which havedefinite shape and volume.
Solids which have definite geometricalshape and sharp melting point are calledcrystalline solid.There are two types of Solids
crystalline solids areShining in light &Anisotropic
Solids which have no definite geometricalshape and no sharp melting point arecalled amorphous solid.
Amorphous solids are1. Not Shining in light2. Particles are not arrangedin regular order.3. Isotropic.
Difference betweenCrystalline solids Amorphous solid1 Have definite geometrical shape 1 Have no definite geometrical shape2 Shine in light 2 Do not Shine in light3 Anisotropic 3 Isotropic4 Have Sharp melting Point 4 Have no Sharp melting Point5 Have definite heat of fusion. 5 Have no definite heat of fusion.
Arragements of atoms/ions / molecules incrystalsCrystal LatticeLattice PointLattice Point
Types of Crystalline Solids1. Ionic crystals are crystals containing ions in the latticepointEg : Na+ Cl- CsCl, MgCl2 Etc
2. Molecular crystals are crystals containing moleculesin the lattice pointEg : Ice, Dry ice, solid ammonia Etc
3. Covalent crystals are crystals containing covalentlybonded atoms in the lattice pointEg : Diamond, Carborundam, graphite and Qurtz
4. Metallic crystals are crystals containing definitegeometrical arrangement of metal atoms in the lattice pointEg : Cu, Zn, Li, Fe Etc.
Crystal LatticeCrystal lattice or space lattice indicates 3-D arrangements ofatoms/ ions/ molecule present in the crystal.Lattice points are the positions ofatoms/ions/molecules that forms crystallattice. When lattice points are joined bystraight line, it results in a definitegeometrical shape of the crystal.
Unit Cell:The unit cell is the smallest portion of the crystal lattice having theshape of the crystal which can repeat in three dimentions to formentire crystal structure.TYPES OF CUBIC UNIT CELL
Coordination Number (C.N)Coordination number of a particle in a crystal is thenumber of its nearest neighbouring particles in acrystal.C.N=6 C.N=8 C.N=12
TYPE OF CUBIC LATTICESimple cubeThe unit cell has eight lattice points at theeight corners of the cube. It also known asprimitive or basic unit cellCoordination Number =8
Body centred cubeThe unit cell has nine lattice points at theeight corners of the cube and one at thecentre of the body.Coordination Number=8
Face centred cubeThe unit cell has 14 lattice points at the eightcorners of the cube and six at the centres ofthe faces.Coordination Number=12
Calculation of number of particles present in cubic unitcells:The particles present in crystal lattice areshared between severel units. So particlebelongs to one unit cell can be calculated.
RULES:- 1. Paticles present at corner are shared between 8cells. So each unit cell gets the share of 1/8th ofthat particle.2. Paticles present at centre of the face are sharedby 2 cells. So each unit cell gets the share of1/2th of that particle.3. Paticles present at centre of the cube is notshared by any cell. So each unit cell gets a share.4. A particle present at the mid point of an edge ofa crystall is shared by 4 unit cell. So each nuitcell gets a share of 1/4th of particle.number of particles present inSimple cube= 1/8 X 8 = 1 particleBody centred unit cells= (1/8 X 8 ) + 1 = 2 particleFace centred unit cells= (1/8 X 8) + (1/2 X 6) = 4 particle
The simple ionic crystals are made up of onlytwo elements.Eg: NaCl, CaCl2, K2O etc
Ionic crystals are classified in to two typesbased on relative number of positive andnegetive ions.1. AB TYPE CrystalsEg: NaCl, KCl, LiBr, KBr NaI, CsClCrystals having same number of +ve and –ve ions.
1. AB2 and A2B TypeCrystalsCrystals having ions double than the otherEg: CaF2, MgCl2 Na2O EtcLi2O
Ionic radius is defined sa the distancebetween the nucleus of an ion and the pointupto which its nuclear charge has influenceon its electron cloud. It is determined byX- ray Or electron difraction studies.When atomic number of elements increases along aperiod in the periodic table, the ionic radiusdecreases because of the increase in the effectivenuclear charge of the ion.
ION N3- O2- F- Na+ Mg2+Atomic No. 7 8 9 11 12Ionic Radiusin nm0.171 0.140 0.136 0.095 0.06Ion Atomic No. Ionic RadiusF- 9 0.136Cl- 17 0.181Br- 35 0.195I- 53 0.216Li+ 3 0.060Na+ 11 0.095K+ 19 0.133Rb 37 0.148The ionic radiusincreases with theincrease of atomicnumber down the groupbecause of the additionof new Shells.
Radius ratio is the ratio of the size of cation tosize of anion present in an ionic crystal.Radius ratio = r+r-Radius ratio of NaCl = rNa =0.095 = 0.52rCl 0.181Radius ratio of ZnS = 0.40, CsCl =0.93,CaF2=0.73
Relation between radius ratio andCoordination NumberWhen the radius ratio increases, cation issurrounded by more number of anion. Hencelarger the size of cation, higher is thecoordination number.Limiting radiusratioCoordinationNumberShape of themoleculeExample0.155 to 0.225 3 Triangular Boron trioxide0.225 to 0.414 4 Tetrahedral Znic blend0.414 to 0.732 6 Octahedral Rock Salt0.732 to 1.0 8 Body centredcubicCaesium Chloride