A helium has two in its and two around it. Helium nuclei were created during the and so are some of the oldest and commonest objects in the Universe. About one quarter of the mass of the Universe is made up of helium atoms!
As we explain in the of the atom, these two electrons fill the space around the atom so no other electrons can enter it.
If a helium atom meets any other kind of atom, it bounces away. The atom behaves as if it has a very hard shell around it. Atoms like this are called .
Helium has some very unusual properties when it is very cold. It can flow up the walls of containers and escape. It can conduct and with almost no resistance, making it a superconductor.
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