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Shanel Weimann ∙
They have different numbers of valance electrons...
3
4A
The actinides
[Ar]3d74s2
From the elements given, argon shows the least reactivity.
Helium has the highest first ionization energy and francium has the lowest first ionization energy.
Few elements have isotopes. their atomic mass is not a whole number.
Anything that has mass.
Green design
This family is called, after IUPAC nomenclature -- actinoids.