Metalloids are metallic-looking brittle solids<span> that are either semiconductors or exist in semiconducting forms, and have amphoteric or weakly acidic oxides. Typical </span>nonmetals<span> have a </span>dull<span>, coloured or colourless </span>appearance<span>; are </span>brittle<span> when </span>solid<span>; are poor conductors of heat and electricity; and have acidic oxides.</span>