Hey there. For your first question the metalloids of the periodic table represent elements that are involved in doping. These metalloids are split into two major classifications: n-type semiconductors and p-type semiconductors. N-type semiconductors are doped with electron rich atoms and in this case there is an extra free floating electron that can move about the crystalline structure. P-type semiconductors are doped with electron poor atoms and in this case there will be a gap present in the crystalline structure because of the absence of an electron.
For the second question, metals tend to be good electrical and thermal conductors while nonmetals represent poor ones. So basically the more metallic an element then the better it is at conducting. So the trend is as you move from right to left of the periodic table or if you move down any group you become more metallic and therefore a better conductor. Hope this helped. Please let us know if you have any other questions : -D