Well, I guess it has something to do with the configuration of electrons around the nucleus. I do know that metals are metals because of the configuration of electrons around their nuclei. It's because they have a few "extra", not so strongly bound, electrons in their outermost "electron shell" (if that is what you call it in English, too). Oxygen, on the other hand, reacts so strongly with almost everything else also because it has a "shortage" of electrons in its outermost "electron shell".
Lead is a metal but not a "typical metal", rather a "transition metal". More important may be the fact that lead is a "heavy metal" with a large nucleus, and its atomic number is 82, meaning that it has a total of 82 protons and 82 electrons (I think). Tungsten, which is even more efficient at shielding against radiation, has an atomic number of 74, which means that it, too, is a heavy metal, and it has 74 protons and 74 electron, eight fewer than lead. I think the number eight rings a bell, because I know that there are only so many electrons that you can fit into an electron shell, and I think eight might be an important "transition number". (Wouldn't you know that oxygen has atomic number eight?)
But if you are looking for the element with atomic number 66 (74 minus 8), you come to a strange element named dysprosium. Have you heard of it? Didn't think so. The element whose atomic number is 90 (82 plus 8) is thorium. Well, I've heard more about thorium than I've heard about dysprosium, so maybe it's used for something, but it is sure more unusual and more expensive than lead.
Periodic table Ann
