2 Helium H [He] Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr +--------------------+ | 2 _ _ | | | | | | ___ | | | |_| |/ _ \ | | | _ | __/ | | |_| |_|\___| | | | | Helium | | 4.00260 u | +--------------------+ Electron Configuration: 1s2 Electronegativity: Atomic Radius: 140 pm Ionization Energy: 24.587 eV Electron Affinity: Oxidation States: 0 Standard State: Gas Melting Point: 0.95 K Boiling Point: 4.22 K Density: 0.0001785 g/cm3 Family: Noble gas Year Discovered: 1868 Number of Neutrons: 2 Number of Protons: 2 Number of Electrons: 2 Number of Valence: 2 Valency: 0 Group: 18 Period: 1 Shell: s-shell Specific Heat: 5.193 J/g K Radioactive: 0 Occurrence: Natural Source: The big bang