posted by MARK on .
What type of bonding holds the compound, sodium cyanide, together?
The CN bond is covalent. The Na to CN bond is, in most minds, an ionic bond. The electronegativity of C is about 2.1 and that of Na is about 1; therefore, with a difference of about 1 it is polar covalent. Quite, polar, though. A difference in EN of about 1.9 is the 50-50 point between ionic/covalent. A difference >1.9 is more ionic than covalent; a diffrence <1.9 is more covalent than ionic.
Why do you state, "in most minds"? What kind of bond do you think this is and why?
I think many people will tend to call the Na to CN bond an ionic one and the CN bond covalent. That is because most compounds of Na are ionic. But if you look at the electronegativities, Na is about 1 (you can look them up--I'm just quoting from memory) and C is about 2.1 which makes a difference of 1.1 and that is about 25% or so (in round numbers) ionic character and 75% covalent character, again in round numbers. So I think it is proper to call it a polar covalent bond. The C to N bond for the cyanide part has EN for C of 2.1 and EN for N is 3 or 0.9 and that is 80% or more covalent. We could call that polar covalent, too. The problem with questions of this nature (is a certain bond ionic or covalent) is that not everyone agrees on what is ionic and what is covalent. Some make the 50-50 at EN difference of 1.7, others choose 1.9 and still others choose 2.1. Also, some call the bond ionic if it is greater than 50% ionic character and covalent if it is less than 50% ionic character. Finally, some have a sliding scale that they have developed with delta EN less than 1.0 they call covalent, from 1 to 1.8 or so is polar covalent, and above 1.8 or so is ionic. What do you do? Follow your profs lead. You know what s/he calls ionic and what s/he calls covalent. I didn't start out to go on and on but I wanted you to know why I made such a statement as "in some minds".....I hope you come away with the idea that this is a little nebulous. I hope this helps clear things in your mind. Thanks for using Jiskha.