How to determine which molecule is more ionic?

[vuongnaomi1L]

So I understand that BaBr2 is more ionic than BeBr2 because since electronegativity decreases down a group, then the electronegative difference between Ba and Br is greater than the electronegative difference between Be and Br2.

However, I am confused because then why is NaCl a stronger ionic bond than KCl? I thought that since K is lower down in group 1 than Na, then the electronegative difference between K and Cl is greater than the electronegative difference between Na and Cl?

Can someone explain why NaCl disagrees with periodic table trends when it comes to ionic bonds and electronegativity?

[Saumya Tawakley 1E]

I'm not too sure about this, but this may be due to the size of the ions involved. Na+ is smaller than K+, so it forms a shorter bond with Cl- compared to K+. Shorter bonds are also stronger bonds, therefore NaCl has a stronger ionic bond than KCl.

Also, the electronegativity of Na is about 0.93 and of K is about 0.82, so their overall electronegativity differences with Cl (with electronegativity of 3.16) is not that much. That may be why size is a deciding factor in which bond is a stronger ionic bond.

Hope this helped!

[Massimo_Capozza_1G]

I think it depends heavily on the electronegativity. Electronegativity increases from left to right of the table and increases going up the table. I would use this rule of thumb to help figure these problems out.

[Vince Li 2A]

Are you sure that NaCl is stronger than KCl? Just by looking at an electronegativity difference chart, I see that the difference for Na and Cl is 2.1 while the difference for K and Cl is 2.2 Perhaps the source in which you got the the information from is incorrect? I don't see how it would make sense that NaCl is a stronger ionic bond than KCl.

[Kayko Lee 1C]

Yeaaa this seems really iffy I would ask a TA or a UA about this question because I've seen multiple typos in the textbook and sometimes they don't always explain the answers in the manual if this question is one of those cases

[Hailey Qasawadish 2J]

Usually, to find how “ionic” a bond is, you would look at the electronegativity values to find the biggest difference in electronegativity. If you don’t have these values, you would use the periodic trends to find the biggest difference. A general rule is that when they’re farther apart on the periodic table, they have a higher electronegativity values. Again, this is just a general rule! Also, the most covalent would be the one with the smallest electronegativity difference. Hope this helps!

[Kathy_Li_1H]

Hi! I believe the method to determine whether a molecule is more ionic is to compare the electronegativity of the two elements/atoms (which can be judged qualitatively through periodic trends) and if the difference is higher, then the molecule is more ionic.

[chinmayeec 2H]

As a post above mentioned, the reason that NaCl has a stronger ionic bond than KCl has to do with the fact that Na is a smaller cation than K. The smaller bond distance in NaCl allows the ionic bond to be stronger than in KCl.

[rhettfarmer-3H]

to figure out which is more iconic it depends on what the molecule is made out of. For example, more iconic is going to have smaller anions like fluorine because they are less covalent and more negative charges. Whereas, for cations, they are gonna be bigger such as K instead of NA because the smaller cation is more covalent.

[Megan ODonnell 3F]

Determine the difference in electronegativities between the two atoms in the molecule you are examining, and which ever molecule produces the greater difference is the molecule that is more ionic.

[Kelly Singh]

Determine the difference in electronegativities between the two atoms in the molecule you are examining, and which ever molecule produces the greater difference is the molecule that is more ionic.

To add to this, elements on the right side of the periodic table are generally more electronegative than elements on the left side.

[Madeline Ogden 3B]

To restate what others have said, you can tell if a bond is more ionic than another by comparing the difference in electronegativity. If you aren't given the value of each molecule/atom's electronegativity then a good rule of thumb is whichever one has atoms that are further away from each other on the periodic table is going to be the one that's more ionic.