Structure and Composition
| Formula | Tm °C |
|---|---|
| H2 | −259.1 |
| F2 | −219.6 |
| O2 | −218.8 |
| N2 | −210.0 |
| CH4 | −182.4 |
| C2H6 | −181.8 |
| C3H8 | −165.0 |
| C4H10 | −138.3 |
| C5H12 | −129.8 |
| Cl2 | −101.6 |
| C6H14 | −95.3 |
| HBr | −86.8 |
| HF | −80.0 |
| NH3 | −80.0 |
| HI | −50.8 |
| C10H22 | −29.7 |
| HCl | −27.3 |
| Br2 | −7.2 |
| H2O | 0.0 |
| C6H6 | 5.5 |
| I2 | 113.7 |
| S8 | 119.0 |
| C6Cl6 | 220.0 |
- See also
higher alkanes
The term "molecular solid" may refer not to a certain chemical composition, but to a specific form of a material. For example, solid phosphorus can crystallize in different allotropes called "white", "red" and "black" phosphorus. White phosphorus forms molecular crystals composed of tetrahedral P4 molecules. Heating at ambient pressure to 250 °C or exposing to sunlight converts white phosphorus to red phosphorus where the P4 tetrahedra are no longer isolated, but are connected by covalent bonds into polymer-like chains. Heating white phosphorus under high (GPa) pressures converts it to black phosphorus which has a layered, graphite-like structure.
The structural transitions in phosphorus are reversible: upon releasing high pressure, black phosphorus gradually converts into the red allotrope, and by vaporizing red phosphorus at 490 °C in inert atmosphere and condensing the vapor, covalent red phosphorus can be transformed back into the white molecular solid.
| White, red, violet and black phosphorus samples | Structure unit of white phosphorus |
Structures of red | violet | and black phosphorus |
Similarly, yellow arsenic is a molecular solid composed of As4 units; it is metastable and gradually transforms into gray arsenic upon heating or illumination. Some forms of sulfur and selenium are composed of S8 (or Se8) units and are molecular solids at ambient conditions, but they can convert into covalent allotropes having atomic chains extending all through the crystal.
Changes in the chemical composition can have even stronger effects on the bonding in solids. For example, whereas both hydrogen and lithium belong to the first group of the periodic table, LiCl is ionic and HCl is a molecular solid.
Read more about this topic: Molecular Solid
Famous quotes containing the words structure and, structure and/or composition:
“Slumism is the pent-up anger of people living on the outside of affluence. Slumism is decay of structure and deterioration of the human spirit. Slumism is a virus which spreads through the body politic. As other “isms,” it breeds disorder and demagoguery and hate.”
—Hubert H. Humphrey (1911–1978)
“The philosopher believes that the value of his philosophy lies in its totality, in its structure: posterity discovers it in the stones with which he built and with which other structures are subsequently built that are frequently better—and so, in the fact that that structure can be demolished and yet still possess value as material.”
—Friedrich Nietzsche (1844–1900)
“I live in the angle of a leaden wall, into whose composition was poured a little alloy of bell-metal. Often, in the repose of my mid-day, there reaches my ears a confused tintinnabulum from without. It is the noise of my contemporaries.”
—Henry David Thoreau (1817–1862)