<P> The macroscopic physical properties of the noble gases are dominated by the weak van der Waals forces between the atoms . The attractive force increases with the size of the atom as a result of the increase in polarizability and the decrease in ionization potential . This results in systematic group trends: as one goes down group 18, the atomic radius, and with it the interatomic forces, increases, resulting in an increasing melting point, boiling point, enthalpy of vaporization, and solubility . The increase in density is due to the increase in atomic mass . </P> <P> The noble gases are nearly ideal gases under standard conditions, but their deviations from the ideal gas law provided important clues for the study of intermolecular interactions . The Lennard - Jones potential, often used to model intermolecular interactions, was deduced in 1924 by John Lennard - Jones from experimental data on argon before the development of quantum mechanics provided the tools for understanding intermolecular forces from first principles . The theoretical analysis of these interactions became tractable because the noble gases are monatomic and the atoms spherical, which means that the interaction between the atoms is independent of direction, or isotropic . </P> <P> The noble gases are colorless, odorless, tasteless, and nonflammable under standard conditions . They were once labeled group 0 in the periodic table because it was believed they had a valence of zero, meaning their atoms cannot combine with those of other elements to form compounds . However, it was later discovered some do indeed form compounds, causing this label to fall into disuse . </P> <P> Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior: </P>

Explain the position of zero group element in periodic table
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