Hydrogen

This gas has one outer electron so it is
usually placed in
Group 1 - Alkali
Metals
,  but it also only has one free
space so it also seems to fit into
Group
17 - Halogens
.  It has some, but not all
of the properties of both groups so it is
usually set at the top of group 1 with a
space between it and the rest of the
group or it is given a different color than
group 1.
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