The formation of a covalent @B00697@, the two shared electrons of which have come from only one of the two parts of the @M03986@ linked by it, as in the reaction of a @L03508@ and a @L03511@ to form a @L03510@; alternatively, the bonding formed in this way. In the former sense, it is the reverse of @M03989@. '@C01326@' and '@C01328@' are synonymous (obsolescent) terms. The synonym '@D01523@' is obsolete. (The origin of the bonding electrons has by itself no bearing on the character of the bond formed. Thus, the formation of methyl chloride from a methyl @C00907@ and a chloride ion involves coordination; the resultant bond obviously differs in no way from the C–Cl bond in methyl chloride formed by any other path, e.g. by @C01153@ of a methyl radical and a chlorine atom.) The term is also used to describe the number of @L03518@ around a @C00930@ without necessarily implying two-electron bonds.