Helium Helium Helium (from ) is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements. After hydrogen, helium is the second lightest and second most abundant element in the observable universe, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this figure in the Sun and in Jupiter. This
Period 6 element period 6 other metals are incredibly toxic, such as thallium. Period 6 contains the last stable element, lead. All subsequent elements in the periodic table are radioactive. After bismuth, which has a half-life or more than 10 years, polonium, astatine, and radon are some of the shortest-lived and rarest elements known; less than a gram of astatine is estimated to exist on earth at any given time. Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes