Search results
Results from the WOW.Com Content Network
Hexagonal boron nitride (h-BN) is the BN analogue of graphite, consisting of sheets of alternating B and N atoms. These sheets stack with boron and nitrogen in registry between the sheets. Graphite and h-BN have very different properties, although both are lubricants, as these planes slip past each other easily.
The boron group are the chemical elements in group 13 of the periodic table, ... with two atoms of the element bonded covalently with three atoms of oxygen.
The mean oxidation number for the boron atoms is then simply the ratio of hydrogen to boron in the molecule. For example, in diborane B 2 H 6, the boron oxidation state is +3, but in decaborane B 10 H 14, it is 7 / 5 or +1.4. In these compounds the oxidation state of boron is often not a whole number.
Within each layer, boron and nitrogen atoms are bound by strong covalent bonds, whereas the layers are held together by weak van der Waals forces. The interlayer "registry" of these sheets differs, however, from the pattern seen for graphite, because the atoms are eclipsed, with boron atoms lying over and above nitrogen atoms.
β-rhombohedral boron has a unit cell containing 105–108 (ideally exactly 105) atoms. Most atoms form B 12 discrete icosahedra; a few form partially interpenetrating icosahedra, and there are two deltahedral B 10 units, and a single central B atom. [ 32 ]
The bridging boron atoms connect three equatorial boron atoms of three icosahedra and those icosahedra make up a network parallel to the (101) crystal plane (x-z plane in the figure). The bonding distance between the bridging boron and the equatorial boron atoms is 0.1755 nm, which is typical for the strong covalent B-B bond (bond length 0.17 ...
Boron (5 B) naturally occurs as isotopes 10 B and 11 B, the latter of which makes up about 80% of natural boron. There are 13 radioisotopes that have been discovered, with mass numbers from 7 to 21, all with short half-lives, the longest being that of 8 B, with a half-life of only 771.9(9) ms and 12 B with a half-life of 20.20(2) ms.
This anion is a bridged bicyclic molecule, contains oxygen atoms bridging the boron atoms, which are linked to four hydroxyl groups (−OH), one per each boron atom. The anion has a tetrahedral molecular geometry at the two tetracoordinated boron atoms, and has a trigonal planar molecular geometry at the two tricoordinated boron atoms.