The noble gases belong to group 18 of the periodic table and are chemical elements with similar properties. All noble gases have a complete outer shell. None of them have color, odor and all have very low chemical reactivity. There are six of them and they are helium, neon, argon, krypton, xenon and radon. Helium Helium has an atomic number of 2. It has no color, odor or taste. It is also an inert monatomic gas. It is the first of the noble gases in the periodic table. Its melting and boiling points are the lowest of all elements and it exists only as a gas except in extreme conditions. Helium is the second most abundant element in the universe, although it is not normally found naturally on earth but is created by radioactive decay. Helium is one of the few elements with such an escape velocity that, when released into the atmosphere, it disperses into space. Helium is in fact the only element that is found in space before being found on Earth. In 1868, an astronomer named Pierre Janssen was in India observing a solar eclipse. He was using the spectroscope to aid in his observations, and while using it he saw a yellow line in the spectrum, which no one had ever heard of or seen. This indicated the existence of an unknown element. Janssen named it helium after the Greek god Helios, otherwise known as Apollo, who was associated with the sun. Janseen met with a world-famous English astronomer, Sir Joseph Lockyer, best known for his work in the analysis of light waves. Lockyer, just like Janssen, also believed that Janseen had discovered a new element. A few months later he also observed the same spectrum discovered by Janseen. The spectroscope was still a new invention that most of the scientific world made…half of the paper…is invalid. Image by XenonRadonRadon is the final element of the noble gases. Its symbol is 86 and its atomic number is 86. It is colorless, tasteless, odorless and is a gas. It is one of the densest substances that remains a gas under normal conditions. Radon is formed as part of the radioactive decay chains of thorium and uranium as they decay into lead. When radon decays, it produces decay products. These products attach to objects in the air such as dust particles. If these dust particles are inhaled, they can stick to the lungs and cause lung cancer. Several studies have shown that those who breathe radon gas are more likely to get lung cancer than those who don't. This therefore makes radon a considerable danger in workplaces such as machine shops and shipyards. Radon poisoning is second to cigarette smoking, after lung cancer.