Search results
Results from the WOW.Com Content Network
Most biological macromolecules contain few or no halogen atoms. But when molecules do contain halogens, halogen bonds are often essential to understanding molecular conformation. Computational studies suggest that known halogenated nucleobases form halogen bonds with oxygen, nitrogen, or sulfur in vitro.
The term bond-dissociation energy is similar to the related notion of bond-dissociation enthalpy (or bond enthalpy), which is sometimes used interchangeably.However, some authors make the distinction that the bond-dissociation energy (D 0) refers to the enthalpy change at 0 K, while the term bond-dissociation enthalpy is used for the enthalpy change at 298 K (unambiguously denoted DH° 298).
It is sometimes called the mean bond, bond enthalpy, average bond enthalpy, or bond strength. [ 1 ] [ 2 ] [ 3 ] IUPAC defines bond energy as the average value of the gas-phase bond-dissociation energy (usually at a temperature of 298.15 K) for all bonds of the same type within the same chemical species.
The group of halogens is the only periodic table group that contains elements in three of the main states of matter at standard temperature and pressure, though not far above room temperature the same becomes true of groups 1 and 15, assuming white phosphorus is taken as the standard state. [n 1] All of the halogens form acids when bonded to ...
Many metals such as the alkali metals react directly with the electronegative halogens gases to form salts. [7] [8] Salts form upon evaporation of their solutions. [9] Once the solution is supersaturated and the solid compound nucleates. [9] This process occurs widely in nature and is the means of formation of the evaporite minerals. [10]
The halogens, being strongly nonmetallic, prefer to form anions rather than cations in aqueous solution. [57] Anion solvation is complicated because the water molecules point the other way: cations bind to the oxygen atom of water, with the hydrogens facing away, while anions prefer to bond asymmetrically to only one of the hydrogen atoms in a ...
The enthalpy of solution is most often expressed in kJ/mol at constant temperature. The energy change can be regarded as being made up of three parts: the endothermic breaking of bonds within the solute and within the solvent, and the formation of attractions between the solute and the solvent.
Bond cleavage is also possible by a process called heterolysis. The energy involved in this process is called bond dissociation energy (BDE). [ 2 ] BDE is defined as the " enthalpy (per mole ) required to break a given bond of some specific molecular entity by homolysis," symbolized as D . [ 3 ]