The heaviest element is either ununoctium, uranium, iridium or osmium. Ununoctium has the largest atomic weight, which corresponds to the number of protons in the nucleus. This element has 118 protons.
However, ununoctium is a man-made atom. Uranium is the heaviest naturally occurring atom. It has 92 protons and an atomic weight of 238.0289.
On the other hand, the densest elements are osmium or iridium, which are both about twice as dense as lead. Osmium's density is about 22.61 grams per cubic meter, while iridium's density is about 22.65 g/cm3. Several factors go into determining density, including the object's volume, mass and the temperature.