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They have 3 electrons in their outer energy levels (valence layers) - outermost shells.
they share  metallic properties.    Boron is metalloid - less of a metal
they form trivalent oxides  -  B2 O3  al2 O3 etc
they form halides with cl etc
other than boron - they are soft, are reactive, good conducting materials for heat and electricity

All elements in the same column as Boron have
3e- in valence shell