How does electronegativity affect bond strength?

[reyrey389]

How does electronegativity affect bond strength?

whats the strongest bond polar covalent, nonpolar covalent, or ionic
how does electronegativity affect bond strength

some people say the more electronegative the molecule the stronger the bond, so than shouldn't ionic bonds be stronger than covalent bonds? just doesn't make sense...

 

[DrDu]

Bond strength depends on many factors like e.g. the size of the atomic orbitals which form the molecule. You have to state first which of these other parameters you want to keep constant for your question to make sense.
E.g. if you replace one atom in a homonuclear covalent bond with another atom with comparable orbitals but higher or lower EN this tends to weaken the bond.

 

[samblohm]

The farther away the electronegativity of 2 atoms, the stronger the bond generally. Cesium has the lowest, and Fluorine has the highest and the make the strongest ionic bond (well single bond at least). The strongest polar covalent that I can think of is the Carbon-Fluorine bond. And yes ionic bonds are stronger than covalent bonds. Just look at melting points. Ionic compounds have high melting points and covalent compounds have low melting points.

And a good amount of what I said is just in general.

 

[reyrey389]

ye ur right ionic is stronger, i asked my teacher. also how do you determine reactivity from the lewis structures? like how are alkenes more reactive than alkanes when alkenes contain double bonds?

doesnt strong bonds imply less reactivity?

thanks

 

[samblohm]

The reason alkanes don't react is because they are don't have any functional groups. A hydrogen-carbon bond is a more stable alternative to a carbon-carbon double bond. The strength of 2 hydrogen carbon bonds is stronger than one carbon carbon double bond.

And it's kinda tough come up with a rule to determine reactivity from lewis structures.

 

[DrDu]

And yes ionic bonds are stronger than covalent bonds. Just look at melting points.

Carbon: >3500K , Silicium: 1410 K, Boron:2300 K, CsF: 955 K

 

[samblohm]

Were talking about compounds, not elements so what you listed doesn't apply.

 

[Borek]

SiC 3000K, WC 3143K, SiO₂ just below 2000K.

 

[samblohm]

I suppose your right, those are covalently bonded, but I personally would consider them covalent networks vs a more common organic covalent bond. But, like I said, they really are covalent bonds.

 

[DrDu]

Were talking about compounds, not elements so what you listed doesn't apply.

Why? I thought we were talking about covalent vs. ionic bonds. A purely covalent bond is easiest to observe in elements.

 

[samblohm]

Although they are covalent bonds, I would consider those to be covalent networks instead of standard organic covalent bonds.

 

[DrDu]

What is probably also helpful in this discussion is the definition of electronegativity by Pauling:
http://en.wikipedia.org/wiki/Electronegativity
You can see that it is the additional stabilization of the heteronuclear bond as compared to the homonuclear bonds.

 

[sjb-2812]

Although they are covalent bonds, I would consider those to be covalent networks instead of standard organic covalent bonds.

And the bonding in e.g. halite is not a network too?

 

[samblohm]

Halite is made of ionic bonds, so it isn't a covalent network

 

[Borek]

Halite is made of ionic bonds, so it isn't a covalent network

You missed the point of the question. Sjb didn't ask if it is a covalent network, but whether it is a network. Substantial difference.

 

[samblohm]

ok, I think I understand now. Instead of classifying melting point by covalent or ionic bonds, could they be classified by whether or not they are a network?