The Noble Gases
The elements of Group VIII of the Periodic Table are gases which have closed shells and are unreactive chemically. Helium, neon, argon and krypton are used in gas discharge decorative ligthing, called "neon" lights. Argon is used to fill incandescent light bulbs to inhibit the evaporation of the tungsten filaments and increase bulb life. Xenon is used in electronic flash tubes for cameras and other flash tubes.
The densities of the noble gases increase with increasing molecular mass. Helium is about one seventh the density of air and can be used in balloons and lighter-than-air craft. Xenon is about five times the density of air.
Noble gases are used to advantage in environments where corrosion or damage from electrical discharges might occur if the environments were filled with air. One such use is in fluorescent light tubes.