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An example of a dative covalent bond is provided by the interaction between a molecule of ammonia, a Lewis base with a lone pair of electrons on the nitrogen atom, and boron trifluoride, a Lewis acid by virtue of the boron atom having an incomplete octet of electrons. In forming the adduct, the boron atom attains an octet configuration.
Lewis had suggested in 1916 that two atoms are held together in a chemical bond by sharing a pair of electrons. [18] When each atom contributed one electron to the bond, it was called a covalent bond. When both electrons come from one of the atoms, it was called a dative covalent bond or coordinate bond. The distinction is not very clear-cut.
[15] In Lewis theory an acid, A, and a base, B, form an adduct, AB, where the electron pair forms a dative covalent bond between A and B. This is shown when the adduct H 3 N−BF 3 forms from ammonia and boron trifluoride, a reaction that cannot occur in water because boron trifluoride hydrolizes in water. [16]
Owing to the vacant orbital present in Z-ligands, many have incomplete octets which allow them to readily accept a pair of electrons from other atoms. [1] A Z‑function ligand interacts with a metal center via a dative covalent bond, differing from the L‑function in that both electrons are donated by the metal rather than the ligand. [5]
The lone electron pair on the nitrogen atom (N) in ammonia, represented as a line above the N, forms a coordinate bond with a proton (H +). After that, all four N−H bonds are equivalent, being polar covalent bonds. The ion has a tetrahedral structure and is isoelectronic with methane and the borohydride anion.
Adducts between them have the formula X 3 A←DY 3 with a dative covalent bond, shown symbolically as ←, between the atoms A (acceptor) and D (donor). Compounds of group 16 with a formula DX 2 may also act as Lewis bases; in this way, a compound like an ether , R 2 O , or a thioether , R 2 S , can act as a Lewis base.
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 ...
The table above gives properties of the vapor–liquid equilibrium of anhydrous ammonia at various temperatures. The second column is vapor pressure in k Pa . The third column is the density of the liquid phase.