Sapling #13 Hydrogen Bonds

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Jillian Labador 3E
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Joined: Wed Sep 30, 2020 9:42 pm

Sapling #13 Hydrogen Bonds

Postby Jillian Labador 3E » Sun Nov 15, 2020 4:45 pm

Hi! Question 13 on Sapling Learning gives a lewis structure of urea CO(NH2)2 and asks how many hydrogen bonds it can form with water molecules. I thought it was 6 which included hydrogen bonds that formed with the 2 nitrogen atoms and the 4 hydrogen atoms of urea, but sapling says the answer is 8. I was missing the 2 hydrogen bonds formed with oxygen, but since it's not covalently attached to a hydrogen, I thought it couldn't form a hydrogen bond with the hydrogens of the water molecules?

Charlene D 3H
Posts: 102
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Re: Sapling #13 Hydrogen Bonds

Postby Charlene D 3H » Sun Nov 15, 2020 5:01 pm

hi Jill!
I believe that as long as the Hydrogen (from the H2O) is bonding with an N, O, or F and the H is attached to an N, O, or F with a lone pair (which it is bc it's attached to the O in H20), it counts as an H-bond.
I hope this helps!

manisha_joseph_1H
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Joined: Wed Sep 30, 2020 10:01 pm

Re: Sapling #13 Hydrogen Bonds

Postby manisha_joseph_1H » Sun Nov 15, 2020 5:10 pm

Hi! You were correct in identifying that hydrogen bonds could form with the two nitrogen atoms and four hydrogen atoms. I believe that water can also form 2 hydrogen bonds with the oxygen atom due to its high electronegativity in relation to carbon, meaning that oxygen would have a partial negative charge as it pulls the electrons closer to it in the carbon-oxygen bond. As such the partial positive charge of the H atom on water would be attracted to the partial negative charge of the oxygen and would be able to form a hydrogen bond, specifically 2 because the oxygen atoms has two pairs of lone electrons. Hope that helps!

Gina Spagarino 3G
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Re: Sapling #13 Hydrogen Bonds

Postby Gina Spagarino 3G » Sun Nov 15, 2020 6:32 pm

I was also confused by this since the oxygen was bonded to a carbon, but another way to think about it is that both compounds involved in the hydrogen bond have either an N/O/F, but one is bonded to a Hydrogen and the other just needs to have an electron pair to actually form the hydrogen bond. In this case, each pair on the oxygen provides the electrons for hydrogen bonds so there's 2 theoretical H bonds on the O atom.

Sarah Huang 3A
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Re: Sapling #13 Hydrogen Bonds

Postby Sarah Huang 3A » Sun Nov 15, 2020 6:40 pm

Jillian Labador 2F wrote:Hi! Question 13 on Sapling Learning gives a lewis structure of urea CO(NH2)2 and asks how many hydrogen bonds it can form with water molecules. I thought it was 6 which included hydrogen bonds that formed with the 2 nitrogen atoms and the 4 hydrogen atoms of urea, but sapling says the answer is 8. I was missing the 2 hydrogen bonds formed with oxygen, but since it's not covalently attached to a hydrogen, I thought it couldn't form a hydrogen bond with the hydrogens of the water molecules?


Hi Jillian!

I definitely had the same question you did, and you were correct with your initial identifications of hydrogen bonds, but the oxygen also counts because it is a potential hydrogen bonding site! Like Nitrogen, it has a lone pair, but oxygen has 2 pairs of lone pairs, making it have two potential hydrogen bonding sites, which is why it was counted. Even though oxygen is already bonded with carbon, and it does not have a hydrogen attached to it, it is the lone pairs that it has that makes it have the potential to have a hydrogen bond.

I hope that helps!

rhettfarmer-3H
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Joined: Wed Sep 30, 2020 9:59 pm

Re: Sapling #13 Hydrogen Bonds

Postby rhettfarmer-3H » Sun Nov 15, 2020 10:37 pm

Hey,
I think the point of focus is on the lone pairs. You were right about the other pairs being possible but the two you may the miss were the lone pair on nitrogen and the 2 lone pairs on oxygen. I missed this part too. It also depends on lone pairs. Since, o has 2 there are two bonds that can form out of that. and nitrogen has one pair and there is two nitrogen so there are also the other 2 bonds.


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