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Molecular solids have low melting (T m) and boiling (T b) points compared to metal (iron), ionic (sodium chloride), and covalent solids (diamond). [4] [5] [8] [13] Examples of molecular solids with low melting and boiling temperatures include argon, water, naphthalene, nicotine, and caffeine (see table below).
Melting points are typically moderately high, but some combinations of molecular cations and anions yield an ionic liquid with a freezing point below room temperature. Vapour pressures in all instances are extraordinarily low; this is a consequence of the large energy required to move a bare charge (or charge pair) from an ionic medium into ...
Such covalent substances are low-boiling-temperature liquids (such as ethanol), and low-melting-temperature solids (such as iodine and solid CO 2). Macromolecular structures have large numbers of atoms linked by covalent bonds in chains, including synthetic polymers such as polyethylene and nylon, and biopolymers such as proteins and starch.
Molecules that are formed primarily from non-polar covalent bonds are often immiscible in water or other polar solvents, but much more soluble in non-polar solvents such as hexane. A polar covalent bond is a covalent bond with a significant ionic character. This means that the two shared electrons are closer to one of the atoms than the other ...
This means that even room temperature ionic liquids have low vapour pressures, and require substantially higher temperatures to boil. [66] Boiling points exhibit similar trends to melting points in terms of the size of ions and strength of other interactions. [66] When vapourized, the ions are still not freed of one another.
This Wikipedia page provides a comprehensive list of boiling and freezing points for various solvents.
Melting point: High, since melting means breaking covalent bonds (rather than merely overcoming weaker intermolecular forces). [ 5 ] Solid-phase electrical conductivity : Variable, [ 6 ] depending on the nature of the bonding: network solids in which all electrons are used for sigma bonds (e.g. diamond, quartz) are poor conductors, as there are ...
Although hydrogen bonding is a relatively weak attraction compared to the covalent bonds within the water molecule itself, it is responsible for several of the water's physical properties. These properties include its relatively high melting and boiling point temperatures: more energy is required to break the hydrogen bonds between water molecules.