Can a human breathe in an atmosphere that has a gas other than nitrogen?

[FtlIsAwesome]

Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.
From Wikipedia, Earth's Atmosphere

Is possible for a human to breathe in an atmosphere that contains 21% oxygen, but has a different inert gas other than nitrogen?

Also, how do different levels of oxygen affect us?

 

[AlephZero]

See http://en.wikipedia.org/wiki/Breathing_gas for information on both questions.

 

[FtlIsAwesome]

See http://en.wikipedia.org/wiki/Breathing_gas for information on both questions.

This page does have some information I was looking for.
I was thinking of extraterrestrial planets, at roughly 1 atm pressure.
So humans could breathe on a planet with 20 percent oxygen and 80 percent helium? Humans' voices would be higher pitched on this planet.
A planet with neon instead wouldn't change someone's voice.

 

[AlephZero]

This page does have some information I was looking for.
I was thinking of extraterrestrial planets, at roughly 1 atm pressure.
So humans could breathe on a planet with 20 percent oxygen and 80 percent helium? Humans' voices would be higher pitched on this planet.

The important parameter is the partial pressure of oxygen in the mixture. Helium has a much smaller atomic weight from nitrogen, so it depends what you mean by "20%". The safe range of oxygen partial pressures is quite small. The minimum to sustain consciousness is about 16%, but too much for moderate lengths of time (e.g. a few hours) is also toxic.

For example with current space technology, astronauts wearing space suits in a vacuum breathe pure oxygen at 0.2 atm pressure whcih is equivalent to the 20% oxygen in the standard Earth atmosphere, but the reduced pressure makes it easier to design a flexible space suit.

 

[Robot B9]

Helium would not work. In a short time the difference in density would cause there to be too much oxygen at low altitudes as the helium tended to escape from the planet...

Oxygen/nitrogen works cause they have close to the same mass, oxygen about 16 and Nitrogen about 14. But Helium is about 4 and is, as they say, lighter then air.

 

[FtlIsAwesome]

Now thinking about it, I could've gotten a terse answer for the title question from a Google search.

Really what am asking about is extraterrestrial atmospheres and their theoretical properties, so would this post be better suited to a different category like General Astronomy?

Helium would not work. In a short time the difference in density would cause there to be too much oxygen at low altitudes as the helium tended to escape from the planet...

Oxygen/nitrogen works cause they have close to the same mass, oxygen about 16 and Nitrogen about 14. But Helium is about 4 and is, as they say, lighter then air.

Good point.
Neon might work because its number of protons+neutrons is 20.

Some isotopes that are uncommon on Earth, but stable: Ne-21, Ne-22, O-17, O-18, N-15
Some combinations of these isotopes might mix better and therefore have a livable atmosphere, but it probably doesn't matter much.

What would the color of a neon-oxygen atmosphere be, assuming the sun was a G class? Also, how would it affect lifeforms from Earth and how would native lifeforms function?