Which noble gas, lighter than air, is commonly used to fill party balloons? Helium is the standard answer because it is lighter than air, nonflammable, and chemically inert.
A helium-filled balloon rises because helium is less dense than the surrounding atmosphere. Air’s average molar mass is about 29 grams per mole, while helium’s is about 4 grams per mole, creating buoyant lift. Helium atoms are also small, so the gas gradually escapes through latex, causing balloons to deflate.
Helium was first identified in the Sun’s spectrum in 1868 and was named after Helios, the Greek sun god. It was later isolated on Earth in 1895. Although hydrogen provides slightly more lift, it is highly flammable, so helium is preferred for party balloons and passenger airships.
Argon is too dense to lift a balloon, and neon is technically lighter than air but much more expensive and less effective. Helium’s combination of lift and safety makes it the canonical choice.