Is AsI3 Ionic or Covalent and How Can You Tell?

[Jules18]

How do you know whether AsI₃ is ionic or covalent?

I was asked on an exam to name it, and I called it Arsenic triioide when the prof said it was Arsenic (III) iodide.

I asked a sophomore TA one time how to tell when it's covalent, and she said the beginning column of the p subshell elements (the end of the transition metals) is her dividing line. In other words, if they're both on the left right of that line, it's a covalent compound, and if they're on opposite sides it's ionic.
But apparently this is an exception, so she must have been mistaken.

And according to another exam written by students in the chem club, Sb₂Te₃ is ionic, so the dividing line isn't the metal-nonmetal dividing line.
It's like you have to know the electronegativity differences or something, which they never give you.
Does anyone have another rule?


~Jules~

 

[Navin A S]

Yes, there is a more reliable way to determine if a compound is ionic or covalent. The best way to tell is to look at the electronegativity difference between the two elements in the compound. If the difference is greater than 1.7 then the compound is likely ionic, whereas if the difference is less than 1.7 then the compound is likely covalent. In the case of AsI3, the electronegativity difference between arsenic and iodine is 2.2, indicating that it is an ionic compound.

 

[quicknote]

I would like to clarify that the classification of a compound as ionic or covalent is not always straightforward. It depends on the electronegativity difference between the two elements involved. In general, if the electronegativity difference is greater than 1.7, then the compound is considered ionic. If the difference is less than 1.7, then the compound is considered covalent.

In the case of AsI3, arsenic (As) has an electronegativity of 2.18 while iodine (I) has an electronegativity of 2.66. This gives an electronegativity difference of 0.48, which is less than 1.7. This suggests that AsI3 is a covalent compound.

However, there are exceptions to this rule, as you have mentioned with Sb2Te3 being ionic despite having a small electronegativity difference. This is because the electronegativity difference is not the only factor that determines the type of bonding in a compound. Other factors such as the size and charge of the atoms also play a role.

In conclusion, the classification of a compound as ionic or covalent cannot be determined solely based on the elements involved. It requires a deeper understanding of their properties and the factors that influence bonding in compounds.