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Because of helium's relatively low molar (atomic) mass, its thermal conductivity, specific heat, and sound speed in the gas phase are all greater than any other gas except hydrogen. For these reasons and the small size of helium monatomic molecules, helium diffuses through solids at a rate three times that of air and around 65% that of hydrogen ...
The Schrodinger equation for helium, like that of hydrogen, can be solved to accuracies equivalent to the most precise experimental values. Among the additional effects that must be included for these high accuracies include: [12] [13] mass polarization: the dynamics of nucleus around the atomic center of mass. relativity: Breit-Pauli corrections
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 .
The standard atomic weight of a chemical element (symbol A r °(E) for element "E") ... Typically, such a value is, for example helium: A r °(He) = 4.002 602 (2).
Due to its low atomic mass of 3.016 u, helium-3 has some physical properties different from those of helium-4, with a mass of 4.0026 u. On account of the weak, induced dipole–dipole interaction between the helium atoms, their microscopic physical properties are mainly determined by their zero-point energy .
2 He helium-4; Hoffer et al. 0.19085 g/cm 3 (from 20.9730 cm 3 /mole; hcp crystal melting to He-II superfluid at 0 K, 25.00 atm) ... formula weight = 222 Notes
The argument for keeping the term "atomic weight" was primarily that it was a well understood term to those in the field, that the term "atomic mass" was already in use (as it is currently defined) and that the term "relative atomic mass" might be easily confused with relative isotopic mass (the mass of a single atom of a given nuclide ...
Neon is lighter than air (density 0.900 g/L at STP, average atomic mass 20.17 g/mol) and could lift a balloon. Like helium, it is non-flammable. Like helium, it is non-flammable. However, it is rare on Earth and expensive, and is among the heavier lifting gases.