Science, Tech, Math › Science What Is the Most Ideal Gas? Share Flipboard Email Print Science Picture Co/Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated December 06, 2019 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.