What are the intermolecular forces between HBr and HI? 1- Hydrogen bonding 2- Dispersion 3- Ion-dipole 4- Dipole-dipole
The Correct Answer and Explanation is:
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Correct Answer: 2 – Dispersion and 4 – Dipole-dipole
Explanation
Hydrogen bromide (HBr) and hydrogen iodide (HI) are both polar covalent molecules composed of a hydrogen atom bonded to a halogen (bromine or iodine). To determine the types of intermolecular forces (IMFs) between these two molecules, we need to examine their polarity and structural characteristics.
- Dispersion Forces (London Dispersion Forces):
These are present in all molecules, whether polar or nonpolar. Dispersion forces arise due to temporary fluctuations in electron density that create instantaneous dipoles, which induce dipoles in neighboring molecules. Since both HBr and HI have electrons and can experience momentary charge separations, dispersion forces are present between them. - Dipole-Dipole Forces:
HBr and HI are both polar molecules due to the difference in electronegativity between hydrogen and their respective halogens (Br and I). The halogen atoms are more electronegative than hydrogen, creating a partial negative charge on the halogen and a partial positive charge on hydrogen. As a result, dipole-dipole interactions occur between the partially positive hydrogen on one molecule and the partially negative halogen on another molecule. These forces are stronger than dispersion forces in polar molecules. - Hydrogen Bonding:
Hydrogen bonding only occurs when hydrogen is directly bonded to a highly electronegative atom like fluorine (F), oxygen (O), or nitrogen (N). Since neither Br nor I is electronegative enough to form hydrogen bonds, hydrogen bonding is not significant in HBr–HI interactions. - Ion-Dipole Forces:
Ion-dipole forces occur between ions and polar molecules, but HBr and HI are not ionic compounds in their molecular form, so ion-dipole forces are not involved.
Conclusion:
The intermolecular forces between HBr and HI are dispersion forces and dipole-dipole forces. These interactions explain their relatively low boiling points and behavior as gases or liquids under standard conditions.
