Solid State Note

Page # 10 SOLID STATE SOLID STATE CRYSTA LLINE SOLIDS A M ORPHOUS SOLIDS 1 Definite geometry * No definite geometry 2 Long range Order * Short range order 3 Sharp melting point * Do not have sharp m.p. 4 Definite heat of fusion * Do not have definite heat of fusion 5 W hen cut generates plain and smooth surfaces * Forms rough and irregular surfaces 6 Anisotropic ie. they have diferent optical * Isotropic i.e have same properties in all and electrical properties in different directions directions 7 True solids * Pseudo -solids or supercooled liquid 8 eq. Sugar, NaCl, Quartz * eq. Rubber, plastic. Types of Solids Solids Types of Particles Bonding/Attractive forces Examples Molecular Solids (a) Non polar Non-polar Molecules Dispersion Forces H2, N2, He, Ar I2, P4 (b) Polar Polar molecules Dipole-Dipole HCl, HBr, SO2 (C ) H-bonded Polar molecules H-Bonding H2O (ice) Contaning O, N, F & H * Ionic Solids Ions Electrostatic or coulombic LiBr, NaCl, CuSO4 * Covalent Solids atoms Co-valent SiO2, Diamond Or Network solids * Metallic Solids graphite, SiC. P 4O10 Kernels and mobile e Metallic bond Fe, Cu, Rb, Brass Crystal lattice : A well order arrangement of atoms, molecules or ions in 3D space. * 2D lattices – 5 (hexagonal, square, rectangular, rhombic, parallelogram) * 3D lattices (Bravais lattice) – 14 Unit Cell : The smallest 3D portion repeated in a crystal lattice. Types of cubic unit cells: Page # 11 SOLID STATE 1. Primitive unit cell or simple cubic : Particles at all corners of a unit cell. No of particles = Z = 2. Body Centrad Cubic (bcc): Particles at all corners as well as 1 particle at the centre of a unit cell. Z= 3. 1 ×8 + 1 = 2 8 Face centered cubic(fcc): Particles at all corners as well as at the centre of each face Z= 4. 1 ×8 = 1, Rank = 1 8 1 1 ×8 + ×6 = 4 8 2 Rank = 4 End Centered : Particles at all corners as well as at the centre of any 2 opposite faces. Z= 1 1 ×8 + ×2 = 2 8 2 Rank = 2 (Rank = No of atoms per unit cell) Close Packing in One dimension : Close Packing in 2 dimension : A A A (i) CN =2 2 1 A B C 1 2 4 3 Square close packing (ii) CN = 4 1 6 2 5 3 4 Hexagonel close packing CN = 6 Close packing in 3 Dimensions: (a) Simple Cubic (AAA....Pattern) A A A A Layers are placed one over the other such that each row of spheres are vertically as well as horizontally aligned. (CN = 6). Page # 12 SOLID STATE Te tra che dra l Void Octahe dra l Void 1 Open space between 4 spheres of 2 Open space between six touching layers of atoms spheres of 2 layers of atoms 2 4 Spheres lie at the corners of a regular tetrahedron 6 Spheres lie at the vertices of a regular octahedron 3 Smaller Larger 4 There are 2 voids per atom of crystal There is one void per atom in a crystal. 5 Radius ratio is 0.225 Radius ratio is 0.414. 6 O T *** (Trigonal void Cubic voids have radius ratio 0.155 & 0.732 3D close packing in hexagonal close packing Placing third layer over second (i) Covering tetrahedral voids –forms ABAB ...............Pattern or hcp. (ii) Covering octahedral Voids – In this 4th layer spheres are vertically aligned with 1st layer * Form ABC ABC pattern. * Called ccp or fcc (P.E) Packing efficiency = Volume occupied by spheres in unit cell  100 Total Volume of unit cell NO of spheres volume of 1 sphere 100 Volume of unit cell (a = edge length of unit cell) Unit cell Particles Radius of atom(r) P. Efficiency = 1. Simple cubic 1 r= 2. bcc 2 r= 3. hcp, 4 r= ccp, fcc a 2 52.4% 3a 4 a 2 2 68% 74% Page # 13 SOLID STATE Density of unit cell: = M z Z = Rank , M = Molar Mass, NA = 6.022×1023 NA  a3 a3 = Volume of unit cell a = edge length of unit cell Crystal defects : Imperfection in solids –2 types (i) Line defect (ii) Point defect Irregularity in a row ions/atoms are missing from their lattice points. Point defect: 3 types (i) Stoichiometric defects: Those defects which do not effect the formula or stoichiometry of the compound. Types –in Non ionic solids (a) Vacancy defect – When some atoms are missing from their positions or lattice points. It decreases density. (b) Interstitial defect : density of the crystal. When some constituent particles occupy interstitial sites. It increases the Types : In ionic solids (c) Schottky defect * Occurs when equal no (d) * Frenkel defect It occurs, when ions are of cations and anions missing from lattice sites and are missing from their found at other interstitial lattice sites. * Decreases crystal density * Found in those ionic sites. * * No change in density Occurs when cations are smaller than anions compounds which have similar size of cations and (i.e. difference in size large) anions. * Found in those compound * which have high co-ordination. which have low number * eg. NaCl, CsCl, CsBr, AlCl3, AgBr In those compound coordination number * Called Dislocation defect * eq. ZnCl2 AgCl, CuCl, AgBr. Impurity defect (Cation replacement type defect). The defect in which a new cation or anion from outside replaces the existing ones such that electrical neutrality is maintained. eg. NaCl having SrCl2 as impurity. Page # 14 SOLID STATE Non-Stoichiometry defects : The defects in which the molecular formula or stoichiometry of the crystal is disturbed or altered. 2 types (i) Metal excess defect - Cations are more than anions (a) Due to anionic vacency - Some anions are missing from their lattice sites and their positions are occupied by electrons (Called F-centres or coloured centres-farbenzenter) It makes the crystal paramagnetic and imparts colour to the crystal. It makes NaCl  Yellow KCl  Violet LiCl  Pink (b) Due to extra cations at interstitial sites - When ZnO is heated it turns yellow. 1 Heat ZnO Zn+2 + O2 + 2e, there will be excess of Zn+2 ions in the crystal which occupy intersti2 tial sites and the electrons lost by oxide ions occupy neighbouring interstitial sties. (ii) Metal deficiency defect. - It occurs in those crystals in which their cations show variable oxidation states. The charge of missing cations is taken by neighbouring cations. In FeO, some Fe+2 are missing. Electrical neutrality is maintained by oxidation of Fe+2 to Fe+3 which leads to change in stoichiometry. eq. [Fe0.93 O1.0, Ni0.98 O1.8 ] Types of solids on the basis of electrical conductivity Conductivity (k) Forbidden Zone Examples Conductors 10 ohm m Over lapped Metal Insulators ohm–1m–1 large MnO, CaO, NiO, CN, TiO2, Fe2O3 ohm–1m–1 small Si, Ge 7 10-20 to 10-10 Semiconductors 10-6 to 104 –1 –1 Pure semiconductors or Intrinsic semiconductors - have low conductivity at room temperature - Conductivity increases by adding impurity (Called doping) Doped Semiconductors :Called Extrinsic semiconductors * Possess high conductivity 2 Types n-Type semiconductors - When Si crystal is doped with group 15 element such as P, As, Sb or Bi (Pentavalent impurity) * The foreign atom (dopant) uses four of its electons for covalent bonding but 5th electron becomes delocalized and is thus free to contribute to electrical conduction * 'n' stands for negative since electron are negatively charged and are responsible for semiconducting behavior SOLID STATE Page # 15 * p-type semiconductors -produced by doping Si with group 13 element such as B, Al, Ga (Trivalent impurity). The dopant atom has 3 valence electrons which are used for forming 3 covalent bonds with neighbouring Si atoms. The place where 4th valence electron is missing gives rise to an electron deficient site or positive hole. The movement of one electron into the vacancy leaves behind a hole at the neighbouring site which carries a positive charge. The movement of positivity charged holes is responsible for the conduction of current Applications of n-type & p-type semiconductor (1) for making anode used as rectifier. (2) Making n-p n and p-n-p transistors to amplify radio and audio signals (3) Solar cell is photodiode used to convert light energy into electrical energy 13-15 compounds : In Sb, AlP, Ga As; 12-16 compounds : When solid state compound are obtained by combination of elements of group 12 and 16 eq. ZnS, Cds, CdSe, Hg Te Transition metal oxides likes: TiO, CrO2 ReO3 behave like metals *ReO3 behaves like Cu in appearance as well as conductance * VO, VO2, VO3, TiO3 show electrical conductance depending upon temperature. Magnetic properties: Diamagnetic meterials: Those materials which are repelled by magnetic field. Occurs due to presence of paired electrons. eq. Cu+, TiO2, NaCl, C6H6 etc. Ferromagnetic substances: Those substances which are strongly attracted by the magnetic field and show permanent magnetism even in the absence of magnetic field eq. Fe, Co, Ni etc. * CrO2 is used for making magnetic tapes of cassette recorders. Antiferromagnetic substances: The substances in which magnetic moments are aligned in such a way that net magnetic moment is zero eq. MnO  Ferrimagnetism: The substances in which magnetic moments are aligned in parallel and antiparallel directions in unequal numbers resulting in net dipole moment. eq. Fe3O4, MgFe2O4, CuFe2O4  * Glass objects recovered from ancient movements looks milky due to crystallization. * Glass window panes of very old buildings are thick from bottom then at the top. (as glass is super cooled liquid. * AgBr shows both frenkel and schottky deffect. * Coordination number (CN) of spheres with which one sphere is in contact is called its coordination number