Is PbO ionic compound?

In IIT-JAM 2018, There was one question: "which one of the following oxides are ionic?" I have selected $\ce{PbO}$ but according to the official answer key, $\ce{PbO}$ isn't ionic.


Although I know this distinction between ionic and covalent isn't defined sharply. But lead is a metal and oxygen is a non-metal. So according to me, it should be ionic. I tried to find on the internet I couldn't able to find out about $\ce{PbO}$, although $\ce{PbO2}$ is defined in between of ionic and covalent according to this paper. $\ce{PbO}$ should be more ionic than $\ce{PbO2}$ since oxidation state of the lead is lower, it will be less electronegative.


Even $\ce{PbCl2}$ is considered as Ionic according to many books, where chlorine is less electronegative and much bigger in size as compared to oxygen, So at least $\ce{PbO}$ should have more ionic character than $\ce{PbCl2}$ according to the Fazan's rule.


So should I challenge the official answer key? If yes, then on what basis? Which reference should I send to them?


[![enter image description here](https://i.stack.imgur.com/bPelr.jpg)](https://i.stack.imgur.com/bPelr.jpg)


[Iono-Covalent Character of the Metal–Oxygen Bonds in Oxides: A Comparison of Experimental and Theoretical Data](https://www.hindawi.com/journals/apec/2004/519019/abs/)




If you want a reference to challenge the question, try page 248 of [Advanced Study Guide Chemistry](https://books.google.com/books?id=5I6HAgAAQBAJ&pg=PA248&dq=PbO%20%22covalent%22&hl=en&sa=X&ved=0ahUKEwj-zJeh68bZAhVKwVkKHQh1Aa8Q6AEIWDAJ#v=onepage&q=PbO%20%22covalent%22&f=false). There is a table on that page that says the PbO is "ionic". 


 4

There are lots of different thoughts about qualitative assignment of whether $\ce{PbO}$ is ionic or covalent.


So, I think it will be better to approach it quantitatively and for that we can take help of **Hannay-Smith's equation** for calculation of ionic character in any binuclear compound.


**% Ionic Character = [ 16 ($ \Delta\ $E.N.) + 3.5 ($ \Delta\ $E.N.)$^2$ ]**


So, according to Pauling scale of E.N., we have E.N. of $\ce{Pb}$ = 1.87 (thanks to @Mithoron for correcting me) and E.N. of $\ce{O}$ = 3.44.


Now, putting the values we will get the *% ionic character of $\ce{PbO}$ to be 33.75%*, which, unfortunately for you and me (I also appeared in this year IIT-JAM and submitted $\ce{PbO}$ to be ionic),indicates that **$\ce{PbO}$ is predominantly covalent in character.**


 0

One of the greatest errors in all of science is the well-propagated notion that there are "ionic" and "covalent" bonds, as if a bond were always one or the other, and that we can tell them apart by electronegativity difference.


Neither notion is true.


* Bonds always have a mixture of ionic and covalent contributions, even where they are between equivalent atoms like $\ce{H2}$. Nonpolar bonds as in molecular hydrogen have small, opposing ionic contributions that cancel each other out.
* Bonds can show much greater ionic character than would be expected from the electronegativity differential. In many cases, a strong ionic bonding character is driven by molecular-orbital structure rather than electronegativity. For example, in magnesium diboride, the boron forms macromolecular structures with low-energy vacant orbitals and thus tends to become anionic (see [here](https://chemistry.stackexchange.com/a/143849/17175)).


My answer to this question is to get a better textbook when one is available.


 0