Question

What gases are closest to being real gases?

Answer 1

The molecules in an ideal gas do not form intermolecular bonds that affect the gas laws.

Explanation:

Helium would be considered to be the closest to an ideal gas. Helium is completely stable as monatomic atom. With an electro negative considered to be zero, an atom of Helium has no attraction to other Helium atoms. This allows Helium to follow the gas laws even at extremely low temperatures and high pressures.

As a counter example Nitrogen functions as an ideal gas at normal temperatures and pressures. But at very low temperatures Nitrogen becomes a liquid. At temperatures approaching the condensation point for Nitrogen gas, the Nitrogen molecules `N_2` start to form temporary intermolecular attractions that cause Nitrogen to not follow the ideal gas laws.

After Helium the rest of the inert gas family, group VIII would most closely follow the ideal gas laws. All the members of this family or group have electro negativities approaching zero. There is little or no intermolecular attractions or forces between the monoatomic units of these gases.

Hydrogen would not be considered to be closest to an ideal gas.
All of the inert gases would be closer than Hydrogen. However it would be necessary to get close to absolute zero before Hydrogen would condense into a liquid. Hydrogen gas `H_2` is very stable and does not form any significant inter molecular forces, or attractions. This makes Hydrogen close to being an ideal gas.

Answer 2

Hydrogen and helium are the closest to ideal gases because they have both the least amount of excluded volume (thereby bringing its molar volume close to that of an ideal gas), and the weakest intermolecular attractions.

Explanation:

The smaller atoms and molecules have the smallest and least polarizable electron clouds, so so they have the weakest London dispersion forces.

However, they are not perfectly ideal.

For example, at 0 °C and 1 atm, the molar volume of an ideal gas is 22.41 L.

Here is a table of the molar volumes of some gases at these conditions.

`bbul("Element"color(white)(m) barV"/L")`
`color(white)(mll)"He"color(white)(mmll)22.44`
`color(white)(mll)"H"_2color(white)(mmll)22.43`
`color(white)(mll)"Ne"color(white)(mmll)22.42`
`color(white)(mll)"Ar"color(white)(mmll)22.39`
`color(white)(mll)"N"_2color(white)(mmll)22.39`

Helium has the smallest intermolecular forces, but the volume of the molecules causes the molar volume to be greater than 22.41 L.

Hydrogen and neon have stronger attractions, and the molar volumes start to decrease.

In argon and nitrogen, despite the larger molecules, the intermolecular forces are strong enough to make the molar volumes less than 22.41 L.