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Chapter 10. Liquids and Solids

Recommended Article : 【Chemistry】 Chemistry(https://jb243.github.io/pages/1362)


1. Definitions of Liquids and Solids

2. Properties of Liquids

3. Properties of Solids



1. Definitions of Liquids and Solids

⑴ Definition of a Liquid is more ambiguous than that of a Gas or Solid

① Gas : Almost no intermolecular forces

② Solid : Particles are fixed in space

③ Liquid : Fluidic but can’t escape from each other, also used when defining the concept of meniscus

⑵ Definition based on Arrangement (Ordering)

① Gas : No ordering

② Solid : Long-range ordering

③ Liquid : Short-range ordering

⑶ Definition based on Vibrational Amplitude

① Gas

② Solid : When particles vibrate less than half the distance between them in a crystalline structure

③ Liquid : When particles vibrate more than half the distance between them in a crystalline structure

⑷ Liquid Crystal : A state where liquid maintains ordering like a solid

① Nematic Phase : Alignment in the same direction, not orderly

② Smectic Phase : Alignment in the same direction with regular spacing

③ Cholesteric Phase : When the next layer is tilted at a certain angle to the previous layer



2. Properties of Liquids

Surface Tension

Viscosity

⑶ Vapor Pressure

① Vapor Pressure and Boiling Point

○ Vapor Pressure : Pressure exerted by vapor when evaporation and condensation of a liquid reach equilibrium

○ Boiling Point : Pressure at which vapor pressure of a liquid equals the external pressure

○ Normal Boiling Point (Tb) : Boiling point at 1 atmosphere pressure

② Vapor-Liquid Equilibrium (e.g., water)

③ Temperature and Raoult’s Law

○ Transition from vapor phase (steam) to gas phase (vapor) is an endothermic process, i.e., ΔH < 0

○ Increase in temperature ⇒ Equilibrium shift towards endothermic reaction according to Raoult’s Law ⇒ Increase in equilibrium constant (K) ⇒ Increase in vapor pressure

④ Clausius-Clapeyron Equation

○ Formulation : For absolute temperature (T)

○ Derivation

○ Vapor pressures at different temperatures

○ Calculation of enthalpy of vaporization and entropy of vaporization

○ Assumption : Enthalpy and entropy of vaporization do not change with temperature

○ Enthalpy of vaporization calculation : Calculate slope from ln P - 1/T curve and multiply by (-R)

Figure 1. Calculation of enthalpy of vaporization

○ Calculation of entropy of vaporization

⑤ Antoine Equation : Empirical equation to calculate vapor pressure

⑷ Freezing Phenomenon

① Definition : Phenomenon where a substance does not solidify even as the temperature goes below its freezing point, i.e., supercooling (e.g., water)

② Principle : Water takes a long time to form its hexagonal structure, preventing freezing below its freezing point



3. Properties of Solids

⑴ Types of Solids

① Classified into Crystalline Solids and Amorphous Solids

② Crystalline solids have ordered arrangements

Type 1: Metallic Crystals : Metallic bonding (electron sea). Conduct electricity (e.g., Na)

Type 2: Ionic Crystals : Ionic bonding. Conduct electricity only in liquid state (e.g., NaCl)

Type 3: Network Crystals : Covalent bonding. Do not conduct electricity

○ Means to define Avogadro’s number

○ Exception : Carbon crystal conducts electricity in the solid state

Type 4: Molecular Crystals : Intermolecular forces. Do not conduct electricity

⑵ Structure of Metallic Crystals

① Overview

○ Nearest neighbor : Atom or ion closest to a central atom or ion

○ Common coordination number : Number of nearest atoms to a specific atom

○ Coordination number of anion : Number of nearest cations to a specific anion

○ Coordination number of cation : Number of nearest anions to a specific cation

○ A total of 14 types of unit cells in metallic crystals

Figure 2. Key structures of metallic crystals

Figure 3. Hexagonal close-packed structure

② Simple Cubic Structure

○ Shape : Atoms at 8 corners of a cube

○ Number of particles per unit cell : Corner atoms are 1/8 of a sphere

○ Coordination number : 2 along each axis, total of 6

○ Radius relationship : Regarding the length of one side (a)

○ Space occupancy rate : Low, rarely found in nature

○ Density

○ Packing method : Simply stack in a straight line

③ Body-Centered Cubic Structure (BCC)

○ Cr, W, Mo, V, Li, Na, Ta, K, α-Fe, δ-Fe, etc.

○ Shape : Atoms at 8 corners of a cube, and an atom at the center of the cube

○ Physical properties : High melting point and high strength

○ Number of particles per unit cell : Corner atoms are 1/8 of a sphere, center atom is whole

○ Coordination number : Convenient when considering the center atom. 8

○ Radius relationship : Consider 3D diagonal for length (a)

○ Space occupancy rate

○ Density

○ Packing method : Each layer is stacked in a straight line, alternating between layers

④ Face-Centered Cubic Structure (FCC)

○ Al, Ag, Au, Cu, Ni, Pb, Ca, Co, γ-Fe, etc.

○ Shape : Atoms at 8 corners of a cube, atoms at the centers of 6 cube faces

○ Physical properties : High electrical conductivity, excellent ductility

○ Number of particles per unit cell : Corner atoms are 1/8 of a sphere, face atoms are 1/2 of a sphere

○ Coordination number : Consider face atoms. 4 on that face, 4 in front, 4 behind, total of 12

○ Radius relationship : Consider 2D diagonal for length (a)

○ Space occupancy rate : Most densely packed

○ Density

○ Packing method : Each row is stacked slightly off from the surrounding rows

⑤ Hexagonal Close-Packed Structure (HCP)

○ Mg, Zn, Cd, Ti, Be, Zr, Ce, etc.

○ Shape : 6-3-6 unit cells are packed like a beehive

○ Physical properties : Poor electrical conductivity, adhesiveness, and ductility

○ Number of particles per unit cell : Corner atoms are 1/6 of a sphere, hexagonal face atoms are 1/2 of a sphere, 3 internal atoms are singular

○ Coordination number : Easily understood with reference to Figure 2.

○ Radius relationship : Regarding the length of one side (a)

○ Space occupancy rate : Packed most densely like FCC

○ Density

⑥ Crystal Structure of Iron

Table 1. Structure of Iron

⑶ Structure of Ionic Crystals

① Examples of Ionic Crystals

Figure 4. Examples of Ionic Crystals

② Binding Energy of Ionic Bonds

○ Coulomb Potential of a Single Dipole

Figure 5. Coulomb Potential of a Single Dipole

○ Coulomb Potential of 1D Crystal : Multiply Coulomb potential of the central atom in an infinite 1D crystal by Avogadro’s number

○ Coulomb Potential of NaCl Crystal : Multiply Coulomb potential of the central atom in an infinite 3D crystal by Avogadro’s number

○ Coulomb Potential of CsCl Crystal : Multiply Coulomb potential of the central atom in an infinite 3D crystal by Avogadro’s number

○ Lattice Energy : Absolute value of Coulomb potential. Lower lattice energy leads to higher solubility

○ Binding Energy of Ionic Bonds = - Metal Ionization Energy + Non-metal Electron Affinity + Lattice Energy

○ Metal Ionization Energy : E(Na+(g)) - E(Na(g))

○ Non-metal Electron Affinity : E(Cl(g)) - E(Cl-(g))

○ Lattice Energy : E(Na+(g)) + E(Cl-(g)) - E(NaCl(s))

○ Binding Energy of Ionic Bonds : E(Na(g)) + E(Cl(g)) - E(NaCl(s))

③ Holes in FCC Structure

○ Two types of holes in FCC structure

○ Tetrahedral interstice : 8 tetrahedral interstices centered on each corner atom in FCC structure

○ Octahedral interstice : 4 octahedral interstices exist, as illustrated below

Figure 6. Illustration of Octahedral Interstice Tip

○ Tetrahedral interstices are smaller than octahedral interstices in FCC structure

⑷ Structure of Atomic Crystals

① Structure of Diamond

○ Overall structure of diamond

Figure 7. Overall structure of diamond

○ Unit cell structure of diamond : The unit cell contains 8 atoms

Figure 8. Unit cell structure of diamond

○ Space occupancy rate



Input: 2018.12.30 22:29

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