Metal/Nonmetal Covalent Bond

[ldv1452]

I often hear that metals and nonmetals can only form ionic bonds, but is this true when difference in electronegativity between the atoms is low? Shouldn't they be able to form polor covalent and nonpolar covalent bonds? Or do the electronegativity based predictions fail in these cases?

[Borek]

There is no such thing as purely ionic nor purely covalent bond, it is always some mixture of both. Cesium fluoride is about as ionic as possible, but aluminum chloride is considered to be covalent.

[Gokul43201]

Shouldn't they be able to form polor covalent and nonpolar covalent bonds?What does it take to form a non-polar covalent bond?

[ldv1452]

What does it take to form a non-polar covalent bond?

Electronegativity difference between the atoms of under .5

[alxm]

Look, (since you've posted 3 whole threads on this archaic topic) ionic vs covalent bonds are a century-old, pre-quantum way of looking at things.
Electronegativities were Linus Pauling's way of utilizing the then-new quantum theory to bring some semblance of theoretical justification to the old models. But once you get past high-school chemistry, then you learn the modern, more sophisticated models of bonding such as Valence-Bond theory and Molecular Orbital theory.

Nobody uses the ionic/covalent distinction for anything serious anymore. It's only applied (and then as a label more than a theory) for the simple and obvious cases you learn about when first learning this stuff.

You're basically trying to apply a model nobody uses anymore to describe something that model always failed at.

[Gokul43201]

No one outside of high school teachers and textbooks, perhaps. I've seen high school chemistry courses still asking students to "list 6 differences between chemical change and physical change" or "classify the following compounds as ionic, polar covalent or non-polar covalent" ... and always, any distinction is based on some arbitrary ruling made by someone a century ago.

[ldv1452]

Thanks for the insights. It's good to get a perspective outside of the imitations of textbooks while learning these topics.