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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: CKabes on February 20, 2013, 10:35:33 PM

Title: Boiling Points of Diatomic Acids
Post by: CKabes on February 20, 2013, 10:35:33 PM

The boiling points of the halogens bonded to hydrogen are as follows in degrees C (approx):

HF: 19.5
HCl: -85
HBr: -66.8
HI: -35

Why is it that HCl has the lowest boiling point and not HI? Doesn't HI have the smallest dipole moment, giving it the weakest inter-molecular bonds?

Title: Re: Boiling Points of Diatomic Acids
Post by: Stovn0611 on February 20, 2013, 11:09:22 PM

My guess would be because HI has stronger London dispersion forces, resulting in stronger inter-molecular bonds that compensate for the weaker inter-molecular bonds from the small dipole moment

Title: Re: Boiling Points of Diatomic Acids
Post by: formaldehyde23 on February 20, 2013, 11:53:45 PM

Yes, Stovn0611 is correct. HF has the highest boiling point because it is the hydrogen halide that has hydrogen bonds. HI has the second highest boiling point because it has the second highest intermolecular forces, or the greatest london dispersion force. This is because Iodine is the largest atom.