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→Key Stage 4
: [[Helium]] [[gas]] is less [[density|dense]] than [[air]].
: An [[atom]] of [[Helium]] has two [[electron]]s in its [[Outer Shell|outer shell]].
{| class="wikitable"
|[[File:Helium.png|center|200px]]
|[[File:HeliumSymbol.png|center|200px]]
|-
| style="height:20px; width:200px; text-align:center;" colspan = "2"|[[Helium]] always has 2 [[proton]]s. The most [[Stable Isotope|stable]] [[isotope]] has 2 [[neutron]]s.
|}