Metal + nonmetal = covalent bond?

[pivoxa15]

In textbooks they normally emphasis the fact that when metals and nonmetals bond, the nonmetal takes away an electron from the metal resulting in ionic bonding between the two.

But metal and nonmetal can still result in covalent bonding when the electronegativities between the two are similar for example BiH3 could exist with covalent bonding and polarity? Also PbH4, TiH5, SnH4 even HgH6? How and where does it stop?

 

[Gokul43201]

The terminology is used very loosely, when talking about ionic or covalent bonds.

The more correct terminology only refers to the ionic character of a covalent bond. So the quantity describing the charge separation in the bond is called the percent ionic character (or the polarity). A purely covalent bond (e.g., H2, Cl2, N2, etc.) is said to have 0% ionic character and is also called a non-polar covalent bond. At the other end, is the (idealized) realization of an ionic bond, which has 100% ionic character - for instance, LiF comes pretty close to this limit. All other bonds lie somewhere in between, and are only labeled as covalent, ionic or polar covalent according to the labeler's tastes. They are all covalent bonds with some ionic character (i.e., polar covalent bonds).

http://www.chemistry.mcmaster.ca/esam/Chapter_7/problems.html