Test: Halogen and Noble Gas Family - Chemistry MCQ

Noble gases have completely filled subshells. As a result, there is no vacant room in their valence shell and hence the additional electron has to be placed in an orbital of the next higher shell. Therefore, energy has to be supplied in order to add an electron and so, the electron gain enthalpy of noble gases is positive (> 0).

The melting and boiling points of noble gases are very low. This is because the atoms are held together by very weak Van der Waals forces of attraction in both liquid and solid states. Helium has the lowest boiling point, equal to 4.2 K, among all known substances.

Of all the noble gases, radon is the most soluble in water. Noble gases are non-polar substance, however, when dissolved in water, they are slightly soluble. This is due to dipole induced dipole interactions.

Helium is the lightest and the smallest noble gas, having an atomic number of 2. Owing to its small size and inert nature, it has the unusual property of diffusing through most commonly used laboratory materials such as rubber, glass or plastic.

Noble gases can form compounds in which the gases are entrapped in the cavities of crystal lattices. Such compounds are called clathrates. Only Argon, Krypton, Xenon and Radon are known to form clathrates among the noble gases.

The elements of group 17 have seven electrons in the valence shell and hence their general electronic configuration is ns²np⁵, i.e., ns²np_x²np_y²np_z¹ where n = 2-6. Thus, they contain one electron less than the nearest inert gas configuration.

Enthalpy of dissociation decreases as the bond distance increases from F₂ to I₂ due to a corresponding increase in the size of the atom as we move down the group from F to I. The F-F bond dissociation enthalpy is, however, smaller than that of Cl-Cl and even smaller than that of Br-Br. This is due to the reason that F atom is very small and hence the electron-electron repulsions between the lone pairs of electrons are very large.

Each halogen has one electron less than the nearest inert gas. As a result, halogens are very reactive elements. They readily share their single unpaired electron with other atoms to form covalent bonds. Thus, all halogens exist as diatomic molecules.

Chlorine was discovered in 1774 by Carl Wilhelm Scheele by heating HCl with MnO₂. In 1810, Davy established its elementary nature and suggested the name chlorine on the basis of its colour (Greek, chloros = greenish yellow).

Iodine  exists as solid at room temperature.