ionic bonds

help i have chem test tomorrow and i forgot the electronegativity difference threshold for ionic bonds, some places say 1.7 others say 1.9 and some say 2.0 so i figure i ask vlr

brother is this gen chem

use your textbook bro

Its 1.7

Googled it and found this on Reddit:
[This is literally the most tragic and biggest misconception in chemistry where students think electronegativity difference alone determines ionicity vs covalency. 1.7 / 1.8 / whatever value should not be the black-and-white line that you draw between the two extremes, as there are many exceptions, and wrong conclusions could be drawn if you resort to your approach.

Examples of common exam-exceptions

1. ⁠BF3: is a very common IB molecule, and is a gas and exists as simple molecules even though the B-F EN difference (2.0) says otherwise
2. ⁠Silver compounds: silver has a high electronegativity as far as metals go, and silver-anything other than fluoride will not cross the 1.7 boundary. Yet most silver compounds are treated as ionic compounds
3. ⁠transition metals: theser are not IB-memorization examples, but Cr2O3 is mostly ionic (mp over 2000 oC) and CrO3 is mostly covalent (acidic oxide)

The proper way to use electronegativity on exams is "the highER the EN difference, the MORE polar the bond", but the EN difference alone does not directly indicate ionicity vs covalency, which is determined by experimental / physical data/ chemical properties](https://www.reddit.com/r/IBO/s/ShmKJLqyTl)

Others have already said what I wanted to say, so good luck!