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helium

From Celestopedia

Helium (symbol He, atomic number 2) is an element. The universe's mass is about 23% helium, making it the second most abundant element in the universe, next to hydrogen.[1]

It's boiling and freezing points are lower than any other known substance. Helium is also the only known element that can't be solidified by sufficient cooling at normal atmospheric pressure.[2]

Isotopes[edit | edit source]

Helium only has two known stable isotopes: helium-3 and helium-4. There are a million times more helium-4 atoms than helium-3 atoms.[3]

Helium-3[edit | edit source]

Helium-3 (3He, atomic number 2) is a stable isotope of helium[3] with an atomic weight of 3, 2 protons, and 1 neutron.

It is abundant in The Moon's soil.[4]

Helium-4[edit | edit source]

Helium-4 (4He, atomic number 2) is a stable isotope of helium[3] with an atomic weight of 4, 2 protons, and 1 neutron.[5]

Etymology[edit | edit source]

Helium comes from the Greek word for the sun, helios.[6]

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