Solid State Chemistry PDF

# 1. Solid State ## General Characteristics of Solid State - Definite mass, volume and shape - Short intermolecular distances - Strong intermolecular forces - Fixed lattice positions of the constituent particles - Incompressibility and rigidity ## Classification of the Solid State - Crystalline -...

# 1. Solid State ## General Characteristics of Solid State - Definite mass, volume and shape - Short intermolecular distances - Strong intermolecular forces - Fixed lattice positions of the constituent particles - Incompressibility and rigidity ## Classification of the Solid State - Crystalline - Amorphous (sometimes called pseudo solids or super-cooled liquids) ## Differences Between the Crystalline and Amorphous Solids | Crystalline | Amorphous | | :--------------------------------- | :-------------------------------------------------------------- | | Have definite characteristic geometrical shape | Have irregular shape | | Melt at a sharp and characteristic temperature | Gradually soften over a range of temperature | | When cut with a sharp edged tool, the newly generated pieces are plain and smooth | When cut with a sharp edged tool, the newly generated pieces are with irregular surfaces | | Have definite and characteristic heat of fusion | Do not have definite heat of fusion | | Are true solids | Are pseudo solids | | Anisotropic in nature | Isotropic in nature | | Have long-range order | Have only short-range order | ## Classification of Crystalline Solids (On the basis of the nature of intermolecular forces) ### Molecular Solids - **Non-Polar Molecular Solids:** These consist either atoms or the molecules formed by non-polar covalent bonds. Example: H2, Cl2, I2 - **Polar Molecular Solids:** The molecules in these types of solids are held together by strong dipole-dipole interactions. Example: Solid' SO2, Solid NH3 - **Hydrogen-Bonded Molecular Solids:** The molecules of such solids contain polar covalent bonds between H and F, O or N atoms. Example: Ice (H2O) ### Ionic Solids Ions are the constituent particles; e.g., NaCl, KNO3 ### Metallic Solids Each metal atom is surrounded by electrons; e.g., Fe, Cu ### Covalent or Network Solids Formed by covalent bonds; e.g., diamond, silicon carbide ## Crystal Lattice A regular three-dimensional arrangement of points in space. - There are 14 Bravais lattices. ## Unit Cells There are two categories of unit cells: - **Primitive Unit Cells:** There are seven types of primitive unit cells - - Cubic ($a = b = c$, $\alpha = \beta = \gamma = 90°$); e.g., NaCl - Tetragonal ($a = b \neq c$, $\alpha = \beta = \gamma = 90°$); e.g., CaSO4 - Orthorhombic ($a \neq b \neq c$, $\alpha = \beta = \gamma = 90°$); e.g., KNO3 - Hexagonal ($a = b \neq c$, $\alpha = \beta = 90°$, $\gamma = 120°$); e.g., ZnO - Rhombohedral or Trigonal ($a = b = c$, $\alpha = \beta = \gamma \neq 90°$); e.g., CaCO3 - Monoclinic ($a \neq b \neq c$, $\alpha = \gamma = 90°$, $\beta \neq 120°$) - Triclinic ($a \neq b \neq c$, $\alpha \neq \beta \neq \gamma \neq 90°$); e.g., Na2SO4.10H2O - **Centred Unit Cells:** There are three types of centred unit cells - Body-centred unit cells: Contain one constituent particle at its body centre along with the ones present at corners. - Face-centred unit cells: Contain one constituent particle at the centre of each face along with the ones present at corners. - End-centred unit cells: Contain one constituent particle at the centre of any two faces along with the ones present at corners. ## Number of Atoms in a Unit Cell - Total number of atoms in one primitive cubic unit cell = 1 - Total number of atoms in one body-centred cubic unit cell = 2 - Total number of atoms in one face-centred cubic unit cell = 4 ## Close-Packed Structures - **Coordination Number:** The number of the nearest neighbours of a particle. - **Packing Efficiency:** The percentage of total space filled by the particles. ### Close-Packing in One Dimension: Only one way of arrangement, i.e., the particles are arranged in a row, touching each other. ### Close-Packing in Two Dimensions: Square close-packing in two dimensions. ### Close-Packing in Three Dimensions: Three-dimensional close-packing is obtained by stacking two-dimensional layers (square close-packed or hexagonal close-packed) one above the other. - There are two highly efficient lattices of close-packing - - Hexagonal close-packed (hcp) - Cubic close-packed (ccp) [also called face-centred cubic (fcc) lattice] - In hcp and ccp, 74% space is filled, i.e., packing efficiency = 74%. - The remaining space is present in the form of voids. - There are two types of voids - - Octahedral voids - Tetrahedral voids - The packings other than hcp and ccp are not close packings as they have less packing efficiency. - Packing efficiency in bcc = 68% - Packing efficiency in simple cubic lattice = 52.4% - Number of octahedral voids = Number of close-packed particles - Number of tetrahedral voids = 2 × Number of close-packed particles - In ionic solids, the bigger ions (usually anions) form the close-packed structure and the smaller ions (usually cations) occupy the voids. - The fraction of the octahedral or tetrahedral voids that are occupied depends on the chemical formula of the compound. ## Packing Efficiency Percentage of total space filled by particles: $Packing\ efficiency = \dfrac{Volume\ of\ one\ particle}{Volume\ of\ cubic\ unit\ cell} \times100%$ ## Calculations Involving Dimensions of Unit Cells $Density\ of\ a\ unit\ cell = \dfrac{Mass\ of\ the\ unit\ cell}{Volume\ of\ the\ unit\ cell} = \dfrac{zM}{a^3N_A}$ Where, - $d$ → Density - $z$ → Number of atoms present in one unit cell - $M$ → Molar mass - $a$ → Edge length - $N_A$ → Avogadro's number ## Imperfections in Solids - **Line Defects:** These arise due to irregularities in the arrangement of constituent particles in entire rows of a lattice point. - **Point Defects:** These arise due to irregularities in the arrangement of constituent particles around a point or an atom. - There are three types of point defects: - Stoichiometric - Impurity - Non-stoichiometric - **Stoichiometric Defects (Intrinsic or thermodynamic defects):** - **Vacancy Defect:** - Developed when a substance is heated. - Decreases the density of the substance. - **Interstitial Defect:** - Increases the density of the substance. - In ionic solids, the vacancy and interstitial defects exist as Frenkel and Schottky defects. - **Frenkel Defect (also called dislocation defect):** It occurs when there is a large difference in the size of ions. - **Schottky Defect:** It is a vacancy defect and it decreases the density of the substance. - **Impurity Defects:** These defects arise when foreign atoms are present at the lattice site (in place of the host atoms). - **Non-stoichiometric Defects:** - **Metal Excess Defect:** - Metal excess defect due to anionic vacancies. - Metal excess defect due to the presence of extra cations. - **Metal Deficiency Defect:** Occurs when the metals show variable valency, i.e., the transition metals. ## Classification of Solids on the Bases of Conductivities - Conductors - Insulators - Semiconductors ## Doping Adding an appropriate amount of suitable impurity to increase conductivity. - **n-type semiconductor:** Doped with electron-rich impurities. - **p-type semiconductor:** Doped with electron-deficient impurities. - Semiconductors are widely used in electronic industries. ## Magnetic Properties Magnetic properties of substances originate because each electron in an atom behaves like a tiny magnet. - Classification of substances on the basis of magnetic properties: - **Paramagnetic:** e.g., O2 - **Diamagnetic:** e.g., H2O - **Ferromagnetic:** e.g., CrO2 - **Anti-ferromagnetic:** e.g., MnO - **Ferrimagnetic:** e.g., Fe3O4 - Ferromagnetic substances can be made permanent magnets. - These magnetic properties are used in audio, video and other recording devices.