Ionic and Molecular Compounds

[Dratos]

I'm trying to understand what makes something an ionic or molecular compound. It is my understand, and as a general rule by my teacher, that anything with an electronegativity difference of >1.7 is considered Ionic and something <1.7 is a molecular compound.

 

for instance, CO2 has a electronegative difference of 3.9. (6.4 - 2.5 = 3.9)

 

given my understanding I would categorize this as an Ionic Compound, however when referring to my suggested answers sheet it is in fact a molecular compound. Why?

[Dratos]

I think i figured it out. Ionic compounds are formed from a metal and a non metal. Molecular compounds are formed from two non metals. The electronegativity only applies to molecular compounds and is further categorized by polar covalent and non-polar covalent. Am i on the right track?

[markov79]

I'm trying to understand what makes something an ionic or molecular compound. It is my understand, and as a general rule by my teacher, that anything with an electronegativity difference of >1.7 is considered Ionic and something <1.7 is a molecular compound.

 

for instance, CO2 has a electronegative difference of 3.9. (6.4 - 2.5 = 3.9)

 

given my understanding I would categorize this as an Ionic Compound, however when referring to my suggested answers sheet it is in fact a molecular compound. Why?

 

What scale are you using? I'm pretty sure the ~1.7 rule is used for the Pauling scale (only one I know of), and that's usually considered to be a 4.0 scale. where are you getting the 6.4 from? Wikipedia says Oxygen's En is 3.44 and Carbon's is 2.55, which results in a difference <1.7.

[Dratos]

Sorry i used the wrong values to represent the electronegativity.

 

C 2.5

O2 3.4

(im guessing you dont multiple the 3.4 by 2 to account for two oxygen atoms)

 

with a difference of 0.9. (<1.7)

 

This is a polar-covalent molecular compound. To justify my answer it is because this compound uses a two non-metals. The electronegativity difference only indicates that the electrons are more likely to be floating closer to O2 than to Carbon. Is this correct?

[markov79]

Sorry i used the wrong values to represent the electronegativity.

 

C 2.5

O2 3.4

(im guessing you dont multiple the 3.4 by 2 to account for two oxygen atoms)

 

with a difference of 0.9. (<1.7)

 

This is a polar-covalent molecular compound. To justify my answer it is because this compound uses a two non-metals. The electronegativity difference only indicates that the electrons are more likely to be floating closer to O2 than to Carbon. Is this correct?

 

as far as i know, yeah.

 

going more detailed, though, i think the difference in electronegativity is characteristic of the two atoms you're looking at. that's how the rule arises... because you're looking at two non-metals, their characteristics aren't so different that they will have a huge difference in En. conversely, if you're looking at a metal and a halogen, for example, their characteristics are different enough, so they'll be participating in an ionic bond. i think, then, the chemists kind of decided that a difference of 1.7 was the benchmark for when something is considered ionic or not. so yeah, because you have two non-metals, they wont be that much different. it's not just because they were classified as "non metals" though. it's because they're fundamentally similar in En character. hoping i haven't disgraced my general chem profs here.

[TheBoss]

Sorry i used the wrong values to represent the electronegativity.

 

C 2.5

O2 3.4

(im guessing you dont multiple the 3.4 by 2 to account for two oxygen atoms)

 

with a difference of 0.9. (<1.7)

 

This is a polar-covalent molecular compound. To justify my answer it is because this compound uses a two non-metals. The electronegativity difference only indicates that the electrons are more likely to be floating closer to O2 than to Carbon. Is this correct?

 

CO2 is non-polar covalent. Each bond is polar, as you correctly stated, but the bond dipoles are equal and point in opposite directions, therefore there is no overall dipole moment. Do you have an intro chem textbook? This should have been explained.

[markov79]

CO2 is non-polar covalent. Each bond is polar, as you correctly stated, but the bond dipoles are equal and point in opposite directions, therefore there is no overall dipole moment. Do you have an intro chem textbook? This should have been explained.

 

that too... missed that.