U3L4 - Dipoles and Hydrogen Bonds

What is the primary cause of a bond dipole within a molecule?

• The complete transfer of electrons from the metal atom

• The presence of an equal number of protons and electrons in the nuclei

• The physical distance between two separate polar molecules in a liquid

• Uneven attraction of shared electrons due to differences in electronegativity.

In a molecule of hydrogen fluoride (HF), which atom carries the partial negative charge (δ−) and why?

• Hydrogen, because it loses its only electron to the fluorine atom

• Hydrogen, because the arrow in the dipole diagram points toward it.

• Fluorine, because it is more electronegative and pulls the shared electrons closer.

• Fluorine because it has more protons than hydrogen.

Hydrogen bonding is a specific, strong type of dipole-dipole attraction. It occurs when hydrogen is bonded to which set of elements?

• Any element

• Carbon, nitrogen or oxygen

• Chlorine, bromine or iodine

• Fluorine, oxygen or nitrogen

Which of the following is true regarding the strength of hydrogen bonds compared to other intermolecular forces?

• Hydrogen bonds are equal in strength to the covalent bonds in a molecule.

• Hydrogen bonds are generally stronger than other forces between molecules.

• Hydrogen bonds are the weakest type of attraction between molecules

• The strength of a hydrogen bond is independent of the atom the hydrogen is bonded to.

How does the strength of attractive forces between molecules influence the boiling point of a substance?

• Weaker attractive forces lead to higher boiling point because molecules move faster.

• Stronger attractive forces lead to the higher boiling point because more energy is required to separate the molecules.

• The strength of attractive forces only affects the melting point, not the boiling point

• Stronger attractive forces lead to a lower boiling point because the molecules are more stable.

What role does energy transfer play when a substance undergoes a phase change from a liquid to a gas?

• Energy is used to break the covalent bonds within the molecules, turning them into individual atoms.

• Energy is transferred out of the substance.

• Energy is transferred to the substance, causing the molecules to separate and weaken their attractive forces.

• Energy creates new electrostatic forces that push the molecules away from each other.