Group 18 Elements | Physical and Atomic Properties#

Introduction#

• Group 18 elements contains six elements: helium, neon, argon, krypton, xenon and radon.
• All these are gases and chemically unreactive and form very few compounds.
• Group 18 elements are also known as noble gases because they have completely filled valence shell orbitals and therefore react with a very few elements only under certain conditions.
• Radon is a radioactive element.

Physical Properties of Group 18 Elements#

• All the noble gases are monoatomic.
• They are colourless, odourless and tasteless.
• They are sparingly soluble in water.
• They have very low melting and boiling points because the only type of interatomic interaction in these elements is weak dispersion forces.
• Helium has an unusual property of diffusing through most commonly used laboratory materials such as rubber, glass or plastics.
• Helium is a non-inflammable and light gas. Hence, it is used in filling balloons for meteorological observations.

Atomic Properties of Group 18 Elements#

1. Electronic Configuration:#

• All noble gases have general electronic configuration ns²np⁶ except helium which has 1s².
• Many of the properties of noble gases including their inactive nature are ascribed to their closed shell structures.

2. Ionization Enthalpy:#

• The energy required to remove an electron from an isolated gaseous atom in its ground state is known as ionization enthalpy. It is depicted by Δ_iH. It is expressed in Kilojoules per mole (KJ mol^-1).
• Due to stable electronic configuration, these gases exhibit very high ionization enthalpy.
• However, ionization enthalpy decreases down the group with increase in atomic size.

3. Atomic Radii:#

• Noble gases have large atomic size because they have Van der Waals' radii only which are expected to have higher magnitude.
• Atomic radii of group 18 elements increase down the group with increase in atomic number.

4. Electron Gain Enthalpy:#

• When a gaseous atom in ground state gains an electron, energy is absorbed or released. This is known as electron gain enthalpy. It is represented by Δ_egH.
• Since noble gases have stable electronic configurations, they have no tendency to accept the electron and therefore, they have large positive values of electron gain enthalpy.

Questions#