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Please explain why the intermolecular forces in a covalent molecule is...

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dropintheocean | Student, Grade 12 | (Level 1) Honors

Posted May 19, 2012 at 8:40 AM via web

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Please explain why the intermolecular forces in a covalent molecule is weak.

http://gcserevision101.wordpress.com/chemistry/

^ this is the website I'm on, scroll down to the C2-2: Structures and Bonding, then keep going to the picture of covalent molecules. How come the intermolecular forces are weaker than the strong bonds? I understand the covalent bonding, but not the intermolecular force bit. Simple explanations please! Thank you!

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mlsiasebs | College Teacher | (Level 1) Associate Educator

Posted May 19, 2012 at 12:49 PM (Answer #1)

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Intermolecular forces are attractions BETWEEN molecules that hold the molecules close to one another. The stronger the IMFs, the more likely that it will be in the solid phase, the weaker the IMFs, the more likely it will be in the gas phase. 

while the covalent bonds are the result of sharing electrons between two atoms, IMFs in polar covalent molecules are the result of the interaction between the partial positive and negative charges that result from the polarity of the molecule. 

Let's look at an example to help. Carbon monoxide is a polar covalent molecule. The carbon and oxygen atoms share electrons which hold them together with a strong bond (imagine they are holding hands). Since oxygen is more electronegative (pulls harder on electrons) than carbon, the electrons are shared unevenly so they spend more time around oxygen than carbon. As a result, carbon has a partial positive charge while oxygen gas a partial negative charge. They aren't full charges because the electrons aren't transferred as in ionic compounds. The partial positive charge on the carbon atom is attracted to the partial negative on the oxygen atom of another molecule. SInce this is just an attractive force between opposite charges, it is much weaker than the bond. 

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