Structure and Properties of Crystals + Allotropes of Carbon

crystalline solids

crystalline solids

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

ionic crystals

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)

metallic crystals

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

molecular crystals

** 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)

covalent network crystals

** 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

diamond

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)

graphite

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)

allotrope

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.

catenation

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

graphene

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)

C60 Fullerene

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)