The definition of an “ideal gas”

An ideal gas is any atom or molecule that exists with a full outer shell. Examples of ideal gases include: H₂, O₂, CO, CO₂, N₂O, N₂, He.

An ideal gas is filled with elements with full outer shells — Ideally, the gasoline tank is completely filled.

Single oxygen and hydrogen atoms are not ideal gases

Example 1

Single hydrogen and oxygen gasses are not ideal gasses as their shells are not full making them reactive

A single oxygen atom is not an ideal gas because it is missing two electrons from its outer shell.

However, an oxygen molecule is an ideal gas because it has a full outer shell of eight electrons. As it consists of two oxygen atoms, it is a diatomic molecule.

Example 2

Carbon monoxide and dioxide are ideal gases because they share electrons meaning both shells are full

In a carbon monoxide (CO) molecule, an atom of oxygen and an atom of carbon share electrons in a triple bond. Both carbon’s need for an outer shell of 8 electrons and oxygen’s need for an outer shell of 8 electrons are satisfied.

Carbon monoxide is an ideal gas. You would not need to reproduce this, but you should know that carbon dioxide (CO₂) is also an ideal gas.

Example 3

Helium is a noble gas but can not exist in pairs but helium is an ideal gas

I am an ideal gas. I have a full outer shell.

Helium is a noble gas with a full outer shell. Its atoms do not exist as diatoms (in pairs).