... just because...

"Four valence electrons" has nothing in particular to do with being a metalloid. Several metals, from tin and lead to titanium, have four valence electrons; so do two metalloids (silicon and germanium, which are less and more metallic respectively). And then there's carbon...

A metalloid is classified partly on the basis of its conductive properties: a metal is a conductor, a metalloid is a semiconductor, and a non-metal is an insulator.

Carbon is right on the non-metal/metalloid borderline with respect to conductivity (especially in its graphite form), but is considered a non-metal for a number of reasons having to do with its chemistry, and with chemical tradition.

Dan Berger