Covalent bond vs. Ionic bond strength

[drdrdrdrdrdrdr]

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Hi everyone,

Bear with me if my question is a little all over...just a little jumbled in my brain about this:

In general, covalent bond is stronger than ionic bonds, correct?
What are some cases where ionic bond is stronger (ie. something in melting point related to packing?)

Also, is it possible to compare covalent bond to hydrogen bond?
Is covalent bond stronger than hydrogen bond (seems so from EK discussion of irreversible inhibition).......................and this leads to my thought of: are all covalent and ionic bonds stronger than any type of intermolecular bond?

If anyone gets me, thanks for the help!!!

 

[MedPR]

Hi everyone,

Bear with me if my question is a little all over...just a little jumbled in my brain about this:

In general, covalent bond is stronger than ionic bonds, correct?
What are some cases where ionic bond is stronger (ie. something in melting point related to packing?)

Also, is it possible to compare covalent bond to hydrogen bond?
Is covalent bond stronger than hydrogen bond (seems so from EK discussion of irreversible inhibition).......................and this leads to my thought of: are all covalent and ionic bonds stronger than any type of intermolecular bond?

If anyone gets me, thanks for the help!!!

Pretty sure covalent bonds are always stronger than ionic bonds.

Yes, covalent bonds are stronger than H-bonds. Individual hydrogen bonds are very weak.

And yes, I believe covalent and ionic are stronger than the other intermolecular bonds.

 

[ljc]

In general, covalent bond is stronger than ionic bonds, correct?

In general, yes.

What are some cases where ionic bond is stronger (ie. something in melting point related to packing?)

Big molecules making covalent bonds (such as diatomic Iodine) will have weaker covalent bonds than small, highly charged ionic bonds like MgCl2.

Is covalent bond stronger than hydrogen bond

Most definitely.

and this leads to my thought of: are all covalent and ionic bonds stronger than any type of intermolecular bond?

Most definitely.

 

[drdrdrdrdrdrdr]

Hey MedPR,

Thanks! I was so fixated on H bond being so strong in high school chem and orgo it is weird to realize they are actually weak

Would you happen to know covalent vs. ionic in terms of melting point etc?

Thanks for always being on top of answering questions, by the way!

 

[ljc]

Hey MedPR,

Thanks! I was so fixated on H bond being so strong in high school chem and orgo it is weird to realize they are actually weak

Would you happen to know covalent vs. ionic in terms of melting point etc?

Thanks for always being on top of answering questions, by the way!

H bonds are the strongest INTERMOLECULAR bonds (unless you count ionic bonds).

I feel like you have a bad definition of "bond" here. Covalent bonds are between two molecules, from the sharing of electrons. This is different than an ionic bond. Ionic bonds form due to electrostatic attraction (a negative attracted to a positive) rather than through the sharing of electrons. One molecule completely gives up its electrons to another, making the first molecule positive and the second negative. This charge is then what forms their bond.

When you melt or boil a covalent molecule, you aren't breaking any INTRAMOLECULAR (inside of a molecule, for instance the covalent bond between oxygen and water in H2O) bonds, you are breaking INTERMOLECULAR (between two molecules, for instance the hydrogen bond between two water molecules) bonds. So to boil a molecule that has purely covalent bonds, you must break any intermolecular forces holding them together.

This is different than ionic bonds. In ionic bonds, a bunch of positive and negative ions stack up in a lattice, each held in place by it's own charge opposite to the ions surrounding it. To make an ionic lattice boil, you need to break these ionic bonds, which are much stronger than the intermolecular forces holding water molecules together. So when you boil an ionic lattice, you are actually dissociating the ionic "compound," and now you have a bunch of gaseous ions floating around (similar to how they dissolve in water). Whereas for a covalent molecule, you still have a water molecule in a gaseous state, it is just no longer held in a liquid because its intermolecular bonds (hydrogen bonds) have been broken due to high kinetic energy.


Edit: some numbers, to help you understand:
H2O boils at 100 degrees celsius. This is the amount of energy it takes to break the intermolecular hydrogen bonds holding any two water molecules together. When H2O boils, it remains as H2O.
NaCl, an ionic compound, boils at 1400 degrees celsius. This is the amount of energy necessary to break a sodium and chloride ion off of the lattice. When you do this, you are breaking their IONIC bonds, and no longer have a NaCl molecule. Instead, you have a sodium atom and a chlorine atom.

When you boil a covalent molecule, you do not break the covalent bonds. When you boil an ionic molecule, you DO break the ionic bonds.

 

[drdrdrdrdrdrdr]

Thank you, that helps clear it up. Esp the ionic lattice! Just what I was looking for

This is such a basic topic, yet it took me a while to accept that covalent, while sharing bond and seems weaker, is stronger than ionic

This one is just not intuitive for me I guess...

 

[MT Headed]

It also depends on the environment. Pure and dry, ionic bonds are stronger than covalent bonds. That's why it takes so much energy to melt or boil NaCl, but you can bust a Br2 molecule apart into bromine atoms with just a little UV light.

In an aqueous environment, covalent bonds are the same strength, but ionic bonds drop down to approximately the same strength as a hydrogen bond.