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Helium (from Greek: ἥλιος, romanized: helios, lit. 'sun') is a chemical element; it has symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table.
A helium atom is an atom of the chemical element helium. Helium is composed of two electrons bound by the electromagnetic force to a nucleus containing two protons along with two neutrons, depending on the isotope, held together by the strong force.
Helium is the 2nd element in the periodic table and has a symbol of He and atomic number of 2. It has an atomic weight of 4.00260 and a mass number of 4. Helium has two protons and two neutrons in its nucleus, and two electrons in one shell.
Element Helium (He), Group 18, Atomic Number 2, s-block, Mass 4.003. Sources, facts, uses, scarcity (SRI), podcasts, alchemical symbols, videos and images.
Detailed decay information for the isotope helium-5 including decay chains and daughter products.
Helium (2 He) (standard atomic weight: 4.002 602 (2)) has nine known isotopes, but only helium-3 (3 He) and helium-4 (4 He) are stable. [4] All radioisotopes are short-lived; the longest-lived is 6 He with half-life 806.92(24) milliseconds .
