which of the molecules listed below can form hydrogen bond? For wich of the molecules would dispersion forces be the only intermolecular force? Give reasons for answer.

A.H2
B.NH3
C.HCl
D.HF

See your post above.

To determine which molecules can form hydrogen bonds and which molecules would have only dispersion forces as the intermolecular force, we need to consider their molecular structures and properties.

Hydrogen bonding occurs between a molecule with a hydrogen atom bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and another electronegative atom with a lone pair of electrons. Hydrogen bonds are stronger than dispersion forces, which are temporary attractive forces between the instantaneous dipoles of neighboring molecules.

Let's analyze each molecule:

A. H2:
Hydrogen gas (H2) consists of two hydrogen atoms covalently bonded together. As it lacks electronegative atoms bonded to hydrogen, it cannot form hydrogen bonds. The only intermolecular force acting on H2 would be dispersion forces.

B. NH3:
Ammonia (NH3) has three hydrogen atoms bonded to a nitrogen atom. Nitrogen is highly electronegative and possesses a lone pair of electrons, making it a potential hydrogen bond donor. Additionally, each hydrogen atom in NH3 can act as a hydrogen bond acceptor. Hence, NH3 can form hydrogen bonds. The intermolecular forces in NH3 include hydrogen bonding and dispersion forces.

C. HCl:
Hydrogen chloride (HCl) consists of a hydrogen atom bonded to a chlorine atom. Chlorine is highly electronegative but does not have a lone pair of electrons. Therefore, HCl can't act as a hydrogen bond donor. The dipole-dipole interactions between the partially positive hydrogen and the partially negative chlorine constitute the intermolecular force in HCl. There are no hydrogen bonds present. Thus, only dispersion forces are responsible for intermolecular attraction in HCl.

D. HF:
Hydrogen fluoride (HF) contains a hydrogen atom bonded to a fluorine atom. Fluorine is highly electronegative and has a lone pair of electrons, making HF capable of acting as both a hydrogen bond donor and acceptor. Therefore, HF can form hydrogen bonds. In addition to hydrogen bonding, dispersion forces also contribute to the intermolecular forces in HF.

In summary, the molecules that can form hydrogen bonds are NH3 and HF. For H2, only dispersion forces are present, while HCl has dipole-dipole interactions (no hydrogen bonding).