Structure and Properties of Crystals + Allotropes of Carbon

Atoms, ions, or molecules that are arranged in a regular repeating pattern is called a crystal lattice. Crystals can be classified as: Ionic solids, Molecular solids, Metallic solids, or Covalent Network solids

Structural Particles: Alternating cations (+ve) and anions (-ve)

Intramolecular Force: Ionic bonds (strong, directional)

Intermolecular Force: ION-ION electrostatic force

• Hardness: Very hard, resists scratching and denting

• Melting Point: Moderate to very high (~1000°C)

• Electrical Conductivity: NO as solid; YES when aqueous and molten

• Solubility: NO in oil; MANY in water → mobbed

• Brittleness: Very brittle, easily broken apart (like charges come into contact, repel and break apart)

Structural Particles: cation “islands” in a “sea” of delocalised electrons

Intramolecular Force: Metallic bonds (strong, non-directional - acts in all directions)

Intermolecular Force: cation-electron electrostatic force (strong - non-directional)

• Hardness: Varies from soft to very hard (stronger electrostatic forces and compactness means cations can be held in place more firmly and resist sliding over each other - the more delocalised electrons, the more it resists denting and scratching)

• Melting Point: Varies from low to high depending on hardness (strong electrostatic forces resist separation)

  Electrical Conductivity: Very good conductors both in solid and liquid state (molten), won’t conduct in water because it won’t dissolve

• Solubility: Not soluble (overall neutral, so nothing to establish forces with the solvent)

• Luster: shiny

• Malleability/Ductility: Malleable (can be hammered) and ductile (can be drawn into wires) → cations slide past each other without coming into contact, hence not breaking the bond

** biggest family!

Structural Particles: Atoms, nonpolar molecules, polar molecules, or molecules H-bonded to F, O, N

Intramolecular Force: Polar or nonpolar covalent bonds (strong, directional force within molecules)

Intermolecular Force: London Dispersion < Dipole-Dipole < Hydrogen bonding (weak, somewhat directional)

• Hardness: Soft (weak intermolecular forces + loose messy lattice mean they are “manipulative” and “squishy”)

• Melting Point: Low to moderate, can evaporate directly, most melt below 300°C (weak intermolecular forces → more easily separated; MP of nonpolar solids increases with molar mass, MP of polar molecular solids increases with strength of IMF)

• Electrical Conductivity: POOR, they are insulators (electrons are shared and thus locked in covalent bonds so no ions or electrons can flow → no mobile electrons)

• Solubility: “Like dissolves Like”; in oil YES if NP; in water YES if P

• Brittleness: Low flexibility (weak, loose, messy lattice crumbles under pressure)

** e.g. sand, quartz, diamond, graphite

Formed by very many atoms or molecules into ONE GIANT MOLECULE

Structural Particles: Atoms (C - diamond, graphite, buckyballs; SiC - moissanite; SiO2 - quartz, sand)

Intramolecular Force: Covalent bonds (strong, directional, interlocking)

Intermolecular Force: London Dispersion forces - in some cases

Covalent Network Crystal, tetrahedral (giant crystal lattice), sp3 hybridization and sigma bonds, no IMFs, VERY HARD (10 Mohs)

• Hardness: Very hard (strong direction covalent bonds and tetrahedral network resists denting and scratching)

• Melting Point: Sublimes at 4027°C (strong covalent bonds and tetrahedral network resists separation)

• Electrical Conductivity: No (electrons shared in bonds so no ions or electrons can flow)

• Solubility: No (overall neutral, nothing to establish forces with the solvent)

• Malleability/Ductility: No (complex interlocking network resists flexibility and will break under pressure along fault lines)

Covalent Network Crystal, trigonal planar (layer-like structure, atoms arranged in flat layers of hexagons, between which is a soup of free-floating, delocalised electrons made up of the spare electrons from sp2 hybridization → pi cloud)

• Hardness: Soft (2-D sheets/layers of hexagonal rings of carbon atoms slide past each other)

• Melting Point: Sublimes at 3600°C (London Dispersion forces between sheets resist separation due to size)

• Electrical Conductivity: YES!! (Pi-cloud has mobile electrons)

• Solubility: No (overall neutral, nothing to establish forces with the solvent)

• Malleability/Ductility: FLAKEY (2-D sheets slide past each other; 1-2 Mohs)

Each of two or more different physical forms in which an element can exist; differ in the arrangement of atoms in crystalline solids or in the occurrence of molecules that contain different numbers of atoms.

The bonding of atoms of the same element into a series, called a chain.

Covalent Network Crystal, trigonal planar (thinnest, lightest, strongest, most stretchy material we have ever created, think of it like a single layer extracted from graphite)

• Hexagonal lattice

• Hybridization: sp2 hybridization

• IMFs?: London Dispersion forces

• Conductivity: Excellent conductor (300x more efficient than copper) due to pi-cloud formed by unhybridized p orbitals

• Melting Point: Sublimes at 3625°C

• Solubility: No solubility in water

• Hardness: Very strong (>10 Mohs)

Molecular Crystal (small, only 60 carbons), trigonal planar (60 C arranged as 10 hexagons and 12 pentagons like a soccer ball)

• Hybridization: sp2 hybridization

• IMFs?: Weak London Dispersion forces between C60 molecules

• Conductivity: Poor conductor compared to graphite; fewer delocalised electrons capable of moving from one molecule to the next

• Melting Point: Sublimes at 600°C (IMFs are weaker, thus, MP is low)

• Solubility: No solubility in water

• Hardness: Very strong (>10 Mohs)