What Is the Most Ideal Gas?

The real gas that acts most like an ideal gas is helium. This is because helium, unlike most gases, exists as a single atom, which makes the van der Waals dispersion forces as low as possible. Another factor is that helium, like other noble gases, has a completely filled outer electron shell. As a result, it has a low tendency to react with other atoms.

The ideal gas composed of more than one atom is hydrogen gas. Like a helium atom, a hydrogen molecule also has two electrons, and its intermolecular forces are small. The electrical charge is spread across two atoms.

As gas molecules get larger, they behave less like ideal gases. Dispersion forces increase and dipole-dipole interaction may occur.

When Do Real Gases Act Like Ideal Gases?

For the most part, you can apply the ideal gas law to gases at high temperatures (room temperature and higher) and low pressures. As pressure increases or the temperature drops, intermolecular forces between gas molecules become more important. Under these conditions, the ideal gas law is replaced by the van der Waals equation.