Question: Intermolecular vs Intramolecular Forces

[MDtoBe777]

When determining strength of a compound do you look at its intermolecular or intramolecular forces? For intermolecular forces, we know that H-bonding is the strongest, then dipole-dipole interactions, then London Forces (dipole-induced dipole forces). For intramolecular forces we have ionic and covalent (polar covalent, coordinate covalent) bonds. Which are the strongest intramolecular forces, ionic or covalent? And should we look at intramolecular or intermolecular when determining the strength of the bonds? My guess is intramolecular since this is actually within the compound...whereas intermolecular forces are more for determining physical properties like melting pt, boiling pt, vapor pressure, etc.

Help!

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[blebl34]

intramolecular > intermolecular

ionic > covalent

be aware that in some compounds (metals and salts), the intermolecular forces that hold the molecules together are the same as the intramolecular forces....so you can think of the compound as one big molecule

for example a NaCl crystal is composed entirely of ionic interactions (strong - hence high melting point)

i believe what i have said to be correct, someone correct me otherwise

 

[MoosePilot]

 

[Dr Dean]

intramolecular > intermolecular

ionic > covalent

be aware that in some compounds (metals and salts), the intermolecular forces that hold the molecules together are the same as the intramolecular forces....so you can think of the compound as one big molecule

for example a NaCl crystal is composed entirely of ionic interactions (strong - hence high melting point)

i believe what i have said to be correct, someone correct me otherwise

RARRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR good points. STUDY HARD.

 

[bgreet]

ionic > covalent

I dont know, maybe I'm confused but I thought covalent > ionic?

 

[MoosePilot]

I dont know, maybe I'm confused but I thought covalent > ionic?

No, covalent is a weaker bond than ionic. It's easier to think it's the other way around, sometimes, because of what an ionic compound does in water, but that's a different issue.

 

[bgreet]

No, covalent is a weaker bond than ionic. It's easier to think it's the other way around, sometimes, because of what an ionic compound does in water, but that's a different issue.

Thanks

 

[BioMedGy]

I was with bgreet on this one: I was sure that covalent bonds are stronger than ionic. However, after further research, it seems that the two simply can't be compared like that...its like the ole' apples and oranges analogy.

 

[skiz knot]

I was with bgreet on this one: I was sure that covalent bonds are stronger than ionic. However, after further research, it seems that the two simply can't be compared like that...its like the ole' apples and oranges analogy.

No, they can be compared exactly. Ionic bonds are stronger than covalent. What these substances do in water is because of their polar nature (water is a strong solvent, a different discussion). The terms covalent and Ionic are man-made designations to describe the amount of distribution in the valence electrons of the atoms in the molecule. There is not an inherent difference between the bonding mechanism of an ionic and covalent bond. In an ionic bond, such as Na+Cl-, the "extra" valence electron of Cl- is essentially "given" to Na+. Probability states that it spends the majority of its time with the Na+. In a covalent bond, the probability that an electron is at a given time with any given atom is less. The degree of sharing is not as high in an ionic bond. The valence electron spends "more time" with one atom, but it is not as strongly attracted as in a ionic bond. I like to think of bonding as a tug of war. In a covalent bond, there is a constant back and forth, often with one side having a slight net advantage. In an ionic bond, one side has basically won the rights to the electron.

The important thing to consider is the difference in electronegativites. If the difference is great enough (I can't remember, but I think 3???) it is considered ionic.

I hope I'm not wrong on any of these ideas