Bjerrum defect
Encyclopedia
A Bjerrum defect is a crystallographic defect
which is specific to ice
, and which is partly responsible for the electrical properties of ice. A hydrogen bond
normally has one proton
, but a hydrogen bond with a Bjerrum defect will have either two protons (D defect) or no proton (L defect). The unfavorable defect strain
is resolved when a water molecule pivots about an oxygen atom to produce hydrogen bonds with single protons. Dislocations of ice Ih
along a slip plane create pairs of Bjerrum defects, one D defect and one L defect.
Nonpolar molecules such as methane can form clathrate hydrate
s with water, especially under high pressure. Although there is no hydrogen bond
ing of water molecules when methane is the guest molecule of the clathrate, guest-host hydrogen bonding often forms with guest molecules in clathrates of many larger organic molecules, such as pinacolone
and tetrahydrofuran
. In such cases the guest-host hydrogen bonds result in the formation of L-type Bjerrum defect in the clathrate lattice. Oxygen atoms (in alcohol or carbonyl functional groups) and nitrogen atoms (in amine functional groups) in the guest molecules lead to transient hydrogen bonds and misoriented water molecules in the hydrate lattice.
Crystallographic defect
Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, determined by the unit cell parameters. However, the arrangement of atom or molecules in most crystalline materials is not perfect...
which is specific to ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
, and which is partly responsible for the electrical properties of ice. A hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
normally has one proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
, but a hydrogen bond with a Bjerrum defect will have either two protons (D defect) or no proton (L defect). The unfavorable defect strain
Strain (chemistry)
In chemistry, a molecule experiences strain when its chemical structure undergoes some stress which raises its internal energy in comparison to a strain-free reference compound. The internal energy of a molecule consists of all the energy stored within it. A strained molecule has an additional...
is resolved when a water molecule pivots about an oxygen atom to produce hydrogen bonds with single protons. Dislocations of ice Ih
Ice Ih
thumb|Photograph showing details of an ice cube under magnification. Ice Ih is the form of ice commonly seen on earth.Ice Ih is the hexagonal crystal form of ordinary ice, or frozen water. Virtually all ice in the biosphere is ice Ih, with the exception only of a small amount of ice Ic which is...
along a slip plane create pairs of Bjerrum defects, one D defect and one L defect.
Nonpolar molecules such as methane can form clathrate hydrate
Clathrate hydrate
Clathrate hydrates are crystalline water-based solids physically resembling ice, in which small non-polar molecules or polar molecules with large hydrophobic moieties are trapped inside "cages" of hydrogen bonded water molecules...
s with water, especially under high pressure. Although there is no hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
ing of water molecules when methane is the guest molecule of the clathrate, guest-host hydrogen bonding often forms with guest molecules in clathrates of many larger organic molecules, such as pinacolone
Pinacolone
Pinacolone is an important ketone in organic chemistry. It has an odour reminiscent of peppermint and was discovered in 1866...
and tetrahydrofuran
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...
. In such cases the guest-host hydrogen bonds result in the formation of L-type Bjerrum defect in the clathrate lattice. Oxygen atoms (in alcohol or carbonyl functional groups) and nitrogen atoms (in amine functional groups) in the guest molecules lead to transient hydrogen bonds and misoriented water molecules in the hydrate lattice.