Physical Properties of the Group 17 Elements (Cambridge (CIE) A Level Chemistry): Flashcards

Volatility is the ease with which a substance evaporates. A volatile substance has a low boiling point. In Group 17, fluorine is the most volatile and iodine the least volatile.

Going down Group 17, the halogen molecules have more electrons. This leads to stronger instantaneous dipole-induced dipole (van der Waals') forces between molecules. More energy is needed to separate the molecules, raising the boiling point.

False.

Bond strength generally decreases going down Group 17. As atoms get larger, the bonding pair of electrons is further from the nuclei and less strongly attracted to them, weakening the covalent bond.

Fluorine has a lower bond enthalpy than chlorine because lone pair repulsion between fluorine atoms weakens the F–F bond.

Cl₂ is a yellow-green gas. Br₂ is an orange-brown liquid. I₂ is a grey-black solid. The colours of the halogens get darker going down Group 17.

False.

Fluorine is the most volatile halogen and iodine is the least volatile. Iodine has stronger van der Waals' forces between its larger molecules, making it harder to vaporise.

Halogens are diatomic molecules held together between molecules by weak instantaneous dipole-induced dipole (van der Waals') forces.

Fluorine atoms are very small. When two F atoms bond, their lone pairs are so close together that they cause significant repulsion, counteracting the attraction of the bonding pair to the nuclei. This weakens the F–F bond, giving fluorine an unexpectedly low bond enthalpy.

Larger halogen molecules have more electrons, creating stronger instantaneous dipole-induced dipole forces. These require more energy to overcome, raising boiling points and decreasing volatility going down the group from F₂ to I₂.