Electronegativity and hydrogen bonds (3F.11)

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Chris Tai 1B
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Joined: Sat Aug 24, 2019 12:16 am

Electronegativity and hydrogen bonds (3F.11)

Postby Chris Tai 1B » Sat Nov 09, 2019 2:36 pm

Which of the following molecules are likely to form hydrogen bonds: (a) PH3; (b) HBr; (c) C2H4; (d) HNO2?

Turns out only d would form hydrogen bonds with other molecules, is there a reason that HBr doesn't? I know hydrogen bonds are usually formed when the hydrogen is attached to a N O or F, but are there any other atoms that hydrogen could attach to besides those three to create a hydrogen bond? What's the cutoff in terms of the difference in electronegativity that determines whether or not hydrogen bonds can form between molecules?

Osvaldo SanchezF -1H
Posts: 122
Joined: Wed Sep 18, 2019 12:21 am

Re: Electronegativity and hydrogen bonds (3F.11)

Postby Osvaldo SanchezF -1H » Sat Nov 09, 2019 6:21 pm

For hydrogen bonds to occur, there must be a good overlap between the orbitals which is why many elements on row 2 can form good hydrogen bonds. However, Br is just too big, so the bond will be very poor since the overlap of orbitals between both elements is poor as well. Hydrogen bonds are strong dipole-dipole interactions so pairing it with a high electronegative element is also preferable but Br does not meet this criteria either.

Alex Hitti 3E
Posts: 51
Joined: Sat Aug 17, 2019 12:17 am

Re: Electronegativity and hydrogen bonds (3F.11)

Postby Alex Hitti 3E » Sun Nov 10, 2019 1:15 am

HNO2 is the only ones that will form Hydrogen bonds because there is a greater electronegativity difference between O and H thus making it polar / able to form H-bonds. In the case of Br, Br is too large to have enough electronegativity to pull the electrons more than the H can. H has to bind to a highly polar covalent atom in order to create hydrogen bonds, and N,O,F are the ones that fit the criteria.

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